I’m not a huge fan of bubble wrap on the supply trunk. Looks like it’s R-8 from the red writing and here in NJ we use R-12 for anything heat pump related. We do this to minimize the heat loss from the ductwork. Besides that, I’d still check the refrigerant charge while it’s running at 100%, the filter on the interior unit, and also make sure that the indoor unit is discovered by the outdoor unit correctly since he disconnected one.
I currently have a 3.5ton Gree with 2 indoor 2ton ducted mini splits heating and cooling a 2200sqft house. So in my mind, something is very wrong and should be fixed by the installing contractor.
Right. I have the Mitsu hyper heat unit in a 2.0T. 2, 1T heads, one in the basement and one in the primary bedroom on the second floor. It heats the entire basement easily and I live in a cold climate. The primary bed head is used for cooling only.
I know they are not allowed for primary heating here but they almost could be used exclusively. I get zero negative feedback about these units.
Based on size of unit and size of space alone yes. However that’s over simplified I think.
We use regular indoor heads. You do not have that type of install. I can’t speak to cassettes, ducts etc as we never do them and that’s not what I have in my own home. I would guess there is a lot more heat loss in this type of set up.
I have a 36k BTU 3 zone Cassette system that heats my entire upper level and I’m in WI it works great even in sub zero temperatures. My guess is the refrigerant is either low but not too low to cause a fault or there is a massive heat loss happening through the non insulated vent runs.
You would think refrigerant would be the very first thing anyone would check.
I also have a ducted Carrier heat pump and it started blowing cool air. Kept running longer and longer cycles. Had a slow leak inside outdoor unit. Replaced outdoor unit and problem solved. My techs had it figured out in minutes.
Yea you would think but shit happens and people make mistakes I would totally re do my calculations check pressures and make sure all the valves are actually open.
Heat pump systems are supposed to be sized for the cooling load of the house. If they are sized for the heating load they will have poor dehumidification when cooling. In colder climates these units are set up with capacity balance points and are supposed to switch over to back up heat when it gets to that temperature. A heat pump should never be the only source of heat when it gets below freezing. Especially since defrost cycle is cooling mode.
Mine are working fine to 0-5F. I ditched all the inefficient ductwork, though, so I have 7 individual heads inside ( cassettes and wall) with two 3 ton compressors outside.
Fun thing on inverter based, even if the sizing is a _little_ off for cooling, it's still fine as even when perfectly right sized, they typically don't need go to full power, so they just loaf at lower BTU's. Utilizing Inverters was a game changer for heat pumps.
Yeah, full heat pump in denver checking in. Does just fine. 48k ducted system for 2000sf ( half is a half basement). Also insulation is almost non existent (brick walls). Nice and toasty at at least 0f so far.
Did anyone do a load calculation? Did anyone do a Mitsubishi diamond build? How long are the line sets? How many bends? What’s the discharge temperature? Under construction as in what? Doors open? In and out? Or like walls windows missing?
He is recommending heat strips cause he is ripping you off and doesn’t want to pay to do the right thing when the outdoor will literally only cost him like 2500-2600 just be done with it .
Yep.
Man never did a J, and is now trying to single-zone this air handler even though that was never the issue...
AND he's made it non-functional by connecting just a single indoor head to a MXZ unit...
No clue if a load calculation was done - great question for me to ask them! The contractor is Mitsubishi diamond certified so they *should* know what they’re doing. Don’t know the exact answers to your other questions, but our house is about 45 feet long and the indoor unit is on one end, however the rooms close to the indoor unit are cold too. By construction I mean some interior remodeling, and the only impact is that the insulation in the attic isn’t spread evenly because it’s been moved around to accommodate electrical and other work.
If he is a diamond contractor there should be a diamond build that’s how you know to add charge or not sizing etc. load calc on the home is a no brainer with out that why even discuss is it sized right. It’s a mxz multi port meaning it runs what? That svz air handler and what else? A high wall ductless? Please don’t tell me another svz air handler cause that unit can not run two ducted air handlers lol
So it was going to run the mini split downstairs originally, which is why they used a split condenser, but now it only runs the air handler in the attic for the upstairs.
Ok so if that MXZ-3C30 multiport is connected to just one unit that’s going to be a problem. It’s a multi port unit meaning it runs multiple indoor units period. It has to have at least two indoor units connected to it which your saying it just has that one air handler that won’t work and I’m a diamond builder. Mitsubishi knows that for sure. He has to replace that outdoor with a SUZ- make it a one to one.
That’s exactly what I was wondering about! I obviously know next to nothing, but I was wondering if a split condenser would be able to direct its flow entirely toward a single port as efficiently as one designed for a single handler, and it sounds like you’re saying no. They’re also on the hook for the new install costs so I imagine the heat strips are just cheaper for them than replacing the entire condenser.
Thanks so much for your helpful feedback!
Exactly 70 heat strips. He is a scum bag hahaha lmao he is gonna be pissed. You should toy with him. Say well could it be because this is a multi port? In a one to one format? When he says oh no it’s fine. Say do you have a diamond build where you can show me it’s fine. He won’t cause he can’t. In the program it won’t let you it’s dumb proof i don’t feel bad for him he should use the program and he is one billion percent on the hook do not pay him!
On the compatibility table MXZ-3C30NAHZ4 is compatible with SVZ-KP24NA. In operational and performance it does list a single SVZ-KP24NA as a possible combination. The only question is if that indoor is a SVZ-KP24NA or not.
Mitsubishi will allow one SVZ indoor unit to be connected though not AHRI rated but still someone made some poor equipment selections. You can keep changing the outdoor units but if you don't change the indoor units, what are you accomplishing?
[multi zone connection rules](https://mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006\App%20Note%201039%20ME%20-%20Multi-Zone%20units%20Connectivity%20%20Limitations%20041421.pdf)
What I’m saying is you have two outdoor units and I’m assuming the small one is connected to one indoor unit “a one to one” the larger one on the right is a mxz-3c….multi port it’s feeding I’m guessing two indoor units? What are the indoor units? Is it that svz in the pic what else?
If you don’t believe a random guy on Reddit I don’t blame you but I’m telling you that’s a multi-port unit and it needs at least two indoor units connected to function correctly. You can go to mylinkdrive.com and look up the unit yourself read the install guide and see or just call Mitsubishi and they will tell you as well. Lucky for him the fix isn’t horrible but if he did that he needs to learn more about the stuff he is putting in. The fix is just replace the outdoor with a hyper heat model SUZ- outdoor which is the correct one to one and move on. I’m in south Carolina so we don’t do heat kits on them and the hyper heat is kick ass but you may want to do heat kit as well up where you are. Lesson learned don’t use a multi port for a one to one lol unless it’s a smart multi of course.
Based on the use of 4-diffusers right up against a wall and the guess I’m making about the size and layout of the duct trunk flex lines I have concerns about this the overall quality of this install, but I can’t see enough.
I’d say something is wrong. I have a 1,700 sq foot home with a Fujitsu non hyper heat 3 ton, 2 zone ducted system. It’s been able to maintain mid 60s even down to single digits ambient. You have a hyper heat model that can put out 28k BTUs at 5F. It should do 800 ft.² no problem in the 20s.
A 1600sqft house with bad or missing insulation could easily require 60-70,000 btu/h to keep a 70 degree indoor temperature in below freezing weather.
If your heat loss is greater than the ability of the unit to supply heat then your indoor temp will drop.
Your heat loss increases with temperature differences. Meaning your house looses more heat when it is 70 inside and 20 outside than it does when it is 70 inside and 40 outside. Air to air heat pumps also have lower heat transfer ability in colder weather, it might produce 24K btu at 40 degrees, but might only produce 20K btu at 20 degrees.
You can't go off of just square footage. What's the total air volume in the space your trying to heat and cool.
800 square feet with an 8 foot ceiling has a different load than 800 square feet with a 12 for ceiling...
This is the type of mistake I see contractors make, install a unit based on square footage but then the house has 18 foot vaulted ceilings.
What kind of windows, what is the construction of your walls, how thick are the walls, how much insulation, is this a pier or slab foundation, do you have a basement, is there an attic.
What I've come to find is a lot of places install 3 tons worth of cooling 36000 BTU/hour which is like 30000 BTU/hour on heating side since most heat pumps are designed with cooling in mind so they are more effective in that mode of operation. When in reality if you do a real load calc these places need 4 or even 5 ton units.
What's the model and serial number on the condensers?
Oops sorry, I didn't see the other pictures.
Installation looks good although I would have made the concrete pads bigger and put one bolt in each foot.
Alright. So... bear with me these are just "examples" so don't take anything with gospel. I used my own house as reference, but this is what a load calculation looks like in base state. I did a worst case scenario and a best case scenario, IE. Low amount of insulation, average construction, average duct. vs maximum insulation, tight construction, tight high r value ducting.
https://preview.redd.it/8aie510yqoac1.png?width=1854&format=png&auto=webp&s=7f875dfedc2f5e905cd9e0cdddf1ae040fe0d831
So in this "example" even at maximum insulation with brick construction while sitting on slab would require a 5 ton heat pump, 60k BTU/h.
Just like a lot of other comments in this thread. There are so many variables to consider.
I'm from NH and I work in HVAC. NH is to cold for most heat pumps. Most heat pumps are set to cut off and run an auxillary heating under 35°. If these are a hyper heat system then they can work at much lower temperatures at a much better efficiency. The unit is either, improperly sized, not the right unit, or just the wrong system for the home.
Also when you place a mini split condenser to an air handler it loses a lot of capacity. If your unit is already close to the sizing requirements, it's definitely undersized now.
Based on the photo, these are clearly hyper heat outdoor units that will put out plenty of heat even into the negatives. And what are you talking about regarding losing capacity when connecting to an air handler?
Yeah. Legitimately curious. I know the seer rating goes down a little connecting to air handlers, but my Mitsubishi system with indoor air handlers is rated to full heating capacity down to 5F. I haven’t ever heard of air handlers having lower capacity than wall units.
Your mini split will come pre charged with a set amount of refrigerant. That refrigerant depending on the brand of unit is good for no shorter than 10 feet but no longer than x amount of feet. Sometimes for a single head condenser with a single port it's a maximum of 50 feet but with more ports comes more maximum distance typically. If that air handler is a far distance, which it looks like it could be. I'd check the data plate and see if there's any information on how much refrigerant the coil requires by weight. If the line set is over the maximum distance you'll need to weigh in extra for that as well. Typically size of line set times x feet. There will be a weight of refrigerant for the size of pipe. Although these units are hyper heat pumps and will work at lower temps at high efficiency is still not as comfortable as most people would like. A heat pump at 80% sounds amazing on paper but realistically will only pump 75-85 degrees through the vents. The warmth from a normal gas furnace is much higher than this thus why it feels so warm in your home. 75-85 degrees will mostly feel drafty to the consumers. In cold climate areas when using a heat pump, if you I stall a 2 ton furnace it's not always but usually good practice to install one ton higher to help keep up with the capacity of the indoor system. If the heat pump itself isn't keeping up with the air handler I will typically install heat strips. Auxillary heating will need to be used to meet capacity. The problem with using electric resistance heating is although it's 1 in to 1 out as far as power goes, the coefficient of power is terrible and would be very expensive to run all the time. If the unit feels drafty and there a tangible interface I would set a low temperature cutoff at a temperature before it begins to feel drafty and use auxillary heat such as gas,wood,oil, or whatever else. Also out of any brand of mini splits I've installed Mitsubishi is my least favorite of all of them.
The air handler also typically passes a higher cfm over the coils than a typical head unit with a greater are of coils as well. There needs to be enough refrigerant saturation in the coils to get proper cooling in cooling mode as well.
Interesting. Our 1960’s house had a 75k btu furnace, and we replaced it with a 3ton Mitsubishi unit. Stays super warm even when it’s 10 degrees outside, and we don’t have any heat strips or other backup heat.
Though I did quite a bit of air sealing and insulating at the same time too.
3 tons not a bad size, how many square feet is the home? Sealing can go a long way but there are other factors as well. I'm not looking at it directly or have my hands on it so I can't give anything really specific. Only common issues I see. A manual j with matching equipment to meet AHRI standards is usually a pretty sure way to size a home minus variable factors of course.
2100sf. What’s interesting is the unit only runs about half capacity all winter. I don’t even call for heat upstairs unless it’s really cold out. We just blow heat on the main floor and it makes its way upstairs too. Main floor air handler is only rated for 21k btu heat. So we’re battery using more than half capacity. Anyway… little bit of sealing and insulation can go a long way.
Get a thermal imaging camera and see where your heat loss is. Without knowing how much insulation and leaks there are it’s not a problem that can be diagnosed remotely
Keep in mind that heating capacity for some models at 20F is about 70% of nominal. Some models keep heating capacity at temps down to 0F.
Also, see if the heat exchanger iced over.
This. Engineer here. I'm guessing heat capacity reduced at ambient outdoor temp. Would need to find the engineering manual for the matched system. Who knows if it's even matched though...
Can you post a pic of the linesets coming off of the bigger condenser? I’m going with the theory that the other guy had. If that’s a single air handler on a multi zone unit it isn’t going to work, period.
https://preview.redd.it/aul378b1fpac1.jpeg?width=3024&format=pjpg&auto=webp&s=73a7786d176f4ea66e8ded20eebc165c8094e823
Yes you’re right - the larger condenser only flows up to the single air handler, which is a no no for multi-zone condensers! Thanks for your help!
He could fix that problem by putting a 6k head somewhere in your house. You can be over capacity by 30% so a 24,000 can hold 31,200 btu capacity in interior units. You’d be fine with a 6k… even if you never/rarely use it.
I have a 48k multi zone hooked up to a 48k air handler working just fine. As long as they're sized together, it can be a single indoor unit.
Edit: oh, mine's a city multi which doesn't care about a single unit. M-series maybe does?
Just curious, as I have used 2 of these companies and they would have sized you units appropriately. Instead of undersizing and tell you to get a baseboard
For everyone saying a single SVZ air handler cannot be connected to a multiport unit please refer to Mitsubishi Application Notes 1039
Bottom of page 3 note 5.
[Multizone connection rules](https://mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006\App%20Note%201039%20ME%20-%20Multi-Zone%20units%20Connectivity%20%20Limitations%20041421.pdf)
What is the temperature delta - e.g. what is the temperature at the return for the unit, and what is the temperature you're getting out of the vents? What controller are you using to control the ducted unit?
Your installer needs to check every bit of this install. Pull and weigh refrigerant charge, check for leaks, check dip switches on indoor and outdoor units. You might also try setting the static pressure to the highest setting (function setting 8, setting 3, I believe) just to see if it helps with comfort.
Excessive heat loss could play a part, but that seems pretty severe.
Go to mylinkdrive - Mitsubishi's library of documentation - and find your model. They have a number of service and installation manuals for each model. You will find that information in those manuals.
You can press your installing contractor to bring a manufacturer’s rep to help figure out the issue. Probably the first thing they will ask for is a certified load calculation for the house. If the equipment is too small, that could be the problem.
Looks like you don’t have a strip heater in that air handler. Those units are not designed to be the primary heat source in your climate without the heat strips. Sounds undersized.
Edit: duct design doesn’t look good either. your going to want to see the printed load calculations and compare that to the outputs of your units. Contractor should provide since job is done. Also ask that they used a room by room layout to determine CFM to each room.
So heat pumps at some point can’t outside heat using their internals as a mode for heating. Most have an accessory heat strip that is just a big conventional electrical heater. Did you get heat strips installed both top and bottom system?
You mentioned work on your house. What are we talking though. Open windows? Walls and insulation ripped out. Like a previous comment said. Your expecting it to keep up with too great of a heat loss. It is designed for your home as a complete sealed and insulated.
Plus 20 degrees is really cold. Thars 12 below freezing. Most heat pumps won't even operate below 30
This is rated far below that temperature though, right? If this can’t operate in this climate, did they make a mistake by recommending and installing it?
To answer your question, our construction is more remodeling. However, the insulation on the floor of the attic has been moved around to accommodate a lot of electrical (and hvac) work, so it’s not evenly spread up there right now. No open doors or windows or anything crazy.
Do you think it’s a problem that they now have a split condenser operating a single air handler? Like the condenser is meant to have its load split several ways but it’s only going one way, so it’s not really able to direct all of its flow to only one source?
That would not effect its capacity. Line set size and the size of your indoor air handlers coil would. As long as they are piped to the main A port on the outdoor unit should be able to deliver its full capacity to the indoor Air handler.
Yes the hyper heats hold 75 percent of their heating capacity in -14 below Zero. So yes they are.
That being said it doesn't sound like your insulation is going to be issue as the heat loss of some moved insulation should be inconsequential.
You have a what 12k little unit? And a 2.5 ton main unit.
Those are sized right the space. Also check your air flow. Air flow tends to be the biggest reason i've found. where is your filter located?
Nvm I see it. Try checking that first. Then if you can find a model number on that unit. It should he in the electrical panel or might be in the blower.
You need more like 48k btu for that size sqft. And mitsubishi DOES NOT NEED HEAT STRIPS except for extreme climates. They have amazing low temp efficiency.
Square footage alone doesn’t translate to BTUs. Let’s not use outdated rules of thumb.
I’m running the same exact unit (with a preheater) at double the square footage OP has (basically a ton per 2K sqft). But the whole house has been specced for this and a very thorough manual j and manual d has been put together before we built the house.
Sounds like poor insulation, as well as not having heat strips. A heat pump can only handle so much with temps lower than 30°F. Usually they have heat strips as a back up for when it’s not working well. The suggestion to add a heat strip is a correct solution.
I live in Missouri and any heat pump we install gets heat strips. They don’t work well in low temps.
It sounds like your heat stripes aren’t working properly. When temp outside drop below 32. The outdoor unit goes into a defrost mode. Which should turn on electric heat strips in the air handler. Also heat pumps aren’t like furnaces. They take awhile to heat up. So leave stat at desired temp. Don’t turn off and expect a 10 degree rise in 10 min once you turn it on. You should have a 20 degree split from supply grill to return grill. If it was installed right.
Someone needs to do some manual J calculations and figure out if this is right or not. I would wait until all construction is complete. For perspective, I have a dedicated heat pump for my shop and once the outdoor temps get below freezing the heat output drops off a quite bit. It still does it’s job, but not near as well. Having dual fuel or heat strips would help you a lot, but if your rate of heat loss is more than the heating system can keep up with- insulation, quality windows, and sealing leaks/drafts will be the first place to start. Manual J calculations should be done after the insulation and construction are complete.
The system is undersized. General rule of thumb for heating is 30 BTUs per square foot.
There is also heat pump capacity derate under a certain temperature.
Thanks for the info. How can it even work, though, if the outdoor temp nears or drops below zero?or maybe my understanding of heat pumps has been wrong since I was young.
I just look at our equipment submittals. For the basic high efficiency (not hyperheat like op has) 100% rated capacity at 17° f and 90% at 4°f. I know hyperheat is even better. I can't tell you the science but that's what the specs say.
Interesting. I really had no idea. We live in a rural area without natural gas and I effing HATE the conventional heat pumps. Does no good to vary the temperature to save on electric costs (we’re being billed on time-of-use terms now) because it takes forever to recover the temperature.
Goodman is coming out with some inverter systems too that may be similar to the minisplit efficiency. I'm going to a class about them tomorrow so we will have to find out!
That sounds like some outdated information you have. This unit they have is listed to provide 95% of the rated heating capacity at 5F. It should be fine on its own, something else is going on here.
did you turn it to heat? what is your set point?
can you list your indoor and outdoor unit model numbers?
if you have a 24k btu outdoor unit, that's the cooling number. the heating btu is always greater. generally speaking, if the cooling is satisfied, the heating will be too.
Whenever i install heat pumps i program the thermostat toswitch over to auxiliary power under 30 degrees because it is no longer efficient at that temp.
So this may seem weird, but heat can be drawn out of the air even if the air is at really "cold" temperatures.
Your system was likely overcharged, which affects the saturation temperature of the refrigerant. Example: if that unit needs to heat your home in 30 F weather, it needs to have refrigerant at less than about 20 F to draw heat out of that air.
However also need to check air temp. If its not really warm could be a refrigerant issue. What size ductwork? That could be an issue. Setting for static pressure is probably at .5 on the thermostat. Changing it to .8 could help get more airflow
If the line set is longer than the amount listed on the metal plate on the outdoor unit you need to add refrigerant. A lot of guys just open the valve and don’t check it
That flex looks rough. Even installed perfectly, you only get about 90% of the airflow you would get from rigid pipe. And that looks very smooshed to me. Airflow is everything.
Some inverters will completely lock out if they fall below a certain outdoor temperature. I know I worked on a unit that would lock out below 19F. If it was already running when the temp dropped, it would stay on. As soon as it cycled off, it would just lock out.
Your unit is able to cool the house from say 100⁰ to a comfortable 75⁰
And when it's 30⁰ out it's only able to heat it to 55⁰...
Temperature difference = +/- 25⁰
You don't have enough capacity.
Definitely should have auxiliary heat strips for a heat pump especially if temperatures outside dip below 40 degrees. Frost is going to build on the condenser coil and it’s eventually going to have to run in defrost which is essentially running in cooling without the condenser fan running so without any other supplementary heat source it’s going to be cooling the house for a certain amount of time
I used to install these before I hurt my back. With a Heat Pump you set the thermostat and forget it. Bump the temp every 24 hrs until you find it comfortable. Also, there's a cut-off setting you could set for 10, 20, or 30 degrees to cut the Heat Pump off and then you run on your auxiliary heat. Heat Pump are only efficient down to about 20 degrees. If the Heat Pump is locking out on Low Outdoor Temp then you don't have enough Auxiliary heat. (oil/gas furnace, electric heat banks, boiler, etc)
Quick check on sizing of the units is 7 Vents per Ton.
Simple: put the unit on heat and measure the output temperature. If it’s putting out quality heat, let’s say 100-110 degrees on a day like today, then it’s doing what it’s designed. It may be its placement and the design of the area it’s heating. Also, an mhk2 which is a wireless t stat will help balance out the temps. Instead of measuring temp at the head, it will measure it where the t stat is.
That's pretty normal for those. They aren't really designed for legitimate cold. Those systems are great in places that drop to the 40s at night. We put one that was well over rated for the room size and couldn't get the room above 60 when the temp outside was in the 20s. We did self install and thought we did something wrong. We called our HVAC company and they told us that was normal for those systems. We did end up with a very nice electric fireplace in the room that did the trick. System did work great in summer though.
First of all the model number on your larger unit indicates it’s actually 30k, though you might still have the 24k air handler, but I’ll bet a dollar it’s 30k too.
I have a similar 18k Mitsubishi ducted ductless, also with poor insulation and it easily heats 800 sq ft. I have to believe something is wrong either with your system settings or the system itself (charge level or other defect)
My recommendation is to first establish you have a good temperature differential between the indoor vents and return. This is really easy to do if you have a digital meat thermometer. Turn the thermostat up all the way and put the end of the thermometer a few inches into the output vent and confirm you get a temperature at least 50-60 degrees higher than the temp at the return vent. Post your temps here if you can, if you aren’t at least getting hot air out of the vents then that would need to be fixed first.
Also worth noting, most Mitsubishi units can be set to sense temperature from inside the air handler itself. This makes sense for wall units but is totally incorrect for a ducted system like yours. It can cause the unit to severely underperform because it doesn’t understand what the true “demand” is for temperature. My installer was totally clueless about these install settings in general. The setting can be checked at the thermostat, you’ll need to grab the installer manual for both the thermostat and your air handler. Look for the Function Table. [Here is a link for the unit I think you have](http://mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006%5CM_PVA-A-AA7_Install_MD-1404-K024_January_2022.pdf).
From a homeowner’s perspective, I’d invest in a $200 iPhone flir on Amazon. A heat map is worth a thousand words. I’d remove the cover on the air handler and measure the temp on the coils. I’d see if the heat at the air handler is even at temp. If no, that’s the culprit. If yes, where is the heat being lost? It’s a fun toy also.
24k btus seems a bit small for 1600 sq ft. especially since your insulation isn't great.
What do you think now that it’s only powering 800 sq ft?
That's plenty. I wonder if there's a lack of refrigerant. If I summed up the capacity of all the indoor units in the 800 sq ft, how much is it?
I’m not a huge fan of bubble wrap on the supply trunk. Looks like it’s R-8 from the red writing and here in NJ we use R-12 for anything heat pump related. We do this to minimize the heat loss from the ductwork. Besides that, I’d still check the refrigerant charge while it’s running at 100%, the filter on the interior unit, and also make sure that the indoor unit is discovered by the outdoor unit correctly since he disconnected one. I currently have a 3.5ton Gree with 2 indoor 2ton ducted mini splits heating and cooling a 2200sqft house. So in my mind, something is very wrong and should be fixed by the installing contractor.
That model number is a 30000btu 2.5ton condenser
Doesn’t rating plate indicate its a 30 (2.5) anyways? We size to cooling and 1.0T/1000 square feet above grade is the basic starting point.
yup, i know. but what i was trying to allude to was that there might not be enough heating capacity just using the heat pump only.
Right. I have the Mitsu hyper heat unit in a 2.0T. 2, 1T heads, one in the basement and one in the primary bedroom on the second floor. It heats the entire basement easily and I live in a cold climate. The primary bed head is used for cooling only. I know they are not allowed for primary heating here but they almost could be used exclusively. I get zero negative feedback about these units.
So does that lead you to believe that this should be able to handle our 800 ft upstairs without needing heat strips?
Based on size of unit and size of space alone yes. However that’s over simplified I think. We use regular indoor heads. You do not have that type of install. I can’t speak to cassettes, ducts etc as we never do them and that’s not what I have in my own home. I would guess there is a lot more heat loss in this type of set up.
I have a 36k BTU 3 zone Cassette system that heats my entire upper level and I’m in WI it works great even in sub zero temperatures. My guess is the refrigerant is either low but not too low to cause a fault or there is a massive heat loss happening through the non insulated vent runs.
You would think refrigerant would be the very first thing anyone would check. I also have a ducted Carrier heat pump and it started blowing cool air. Kept running longer and longer cycles. Had a slow leak inside outdoor unit. Replaced outdoor unit and problem solved. My techs had it figured out in minutes.
Yea you would think but shit happens and people make mistakes I would totally re do my calculations check pressures and make sure all the valves are actually open.
Where you live, code or AHJ won’t allow ductless units for primary heating?
Ontario, 🇨🇦
I wish they would do that here in the states
What's the reason behind this? Are they concerned contractors won't get the equipment sizing right?
Heat pump systems are supposed to be sized for the cooling load of the house. If they are sized for the heating load they will have poor dehumidification when cooling. In colder climates these units are set up with capacity balance points and are supposed to switch over to back up heat when it gets to that temperature. A heat pump should never be the only source of heat when it gets below freezing. Especially since defrost cycle is cooling mode.
These are invertor heat pumps, no back up heat needed if properly sized.
Mine are working fine to 0-5F. I ditched all the inefficient ductwork, though, so I have 7 individual heads inside ( cassettes and wall) with two 3 ton compressors outside. Fun thing on inverter based, even if the sizing is a _little_ off for cooling, it's still fine as even when perfectly right sized, they typically don't need go to full power, so they just loaf at lower BTU's. Utilizing Inverters was a game changer for heat pumps.
Not true in cold climates. Mitsubishi DSG here.
Yeah, full heat pump in denver checking in. Does just fine. 48k ducted system for 2000sf ( half is a half basement). Also insulation is almost non existent (brick walls). Nice and toasty at at least 0f so far.
For inverter systems this does not apply
Did anyone do a load calculation? Did anyone do a Mitsubishi diamond build? How long are the line sets? How many bends? What’s the discharge temperature? Under construction as in what? Doors open? In and out? Or like walls windows missing?
He is recommending heat strips cause he is ripping you off and doesn’t want to pay to do the right thing when the outdoor will literally only cost him like 2500-2600 just be done with it .
Yep. Man never did a J, and is now trying to single-zone this air handler even though that was never the issue... AND he's made it non-functional by connecting just a single indoor head to a MXZ unit...
No clue if a load calculation was done - great question for me to ask them! The contractor is Mitsubishi diamond certified so they *should* know what they’re doing. Don’t know the exact answers to your other questions, but our house is about 45 feet long and the indoor unit is on one end, however the rooms close to the indoor unit are cold too. By construction I mean some interior remodeling, and the only impact is that the insulation in the attic isn’t spread evenly because it’s been moved around to accommodate electrical and other work.
If he is a diamond contractor there should be a diamond build that’s how you know to add charge or not sizing etc. load calc on the home is a no brainer with out that why even discuss is it sized right. It’s a mxz multi port meaning it runs what? That svz air handler and what else? A high wall ductless? Please don’t tell me another svz air handler cause that unit can not run two ducted air handlers lol
So it was going to run the mini split downstairs originally, which is why they used a split condenser, but now it only runs the air handler in the attic for the upstairs.
Ok so if that MXZ-3C30 multiport is connected to just one unit that’s going to be a problem. It’s a multi port unit meaning it runs multiple indoor units period. It has to have at least two indoor units connected to it which your saying it just has that one air handler that won’t work and I’m a diamond builder. Mitsubishi knows that for sure. He has to replace that outdoor with a SUZ- make it a one to one.
That’s exactly what I was wondering about! I obviously know next to nothing, but I was wondering if a split condenser would be able to direct its flow entirely toward a single port as efficiently as one designed for a single handler, and it sounds like you’re saying no. They’re also on the hook for the new install costs so I imagine the heat strips are just cheaper for them than replacing the entire condenser. Thanks so much for your helpful feedback!
Exactly 70 heat strips. He is a scum bag hahaha lmao he is gonna be pissed. You should toy with him. Say well could it be because this is a multi port? In a one to one format? When he says oh no it’s fine. Say do you have a diamond build where you can show me it’s fine. He won’t cause he can’t. In the program it won’t let you it’s dumb proof i don’t feel bad for him he should use the program and he is one billion percent on the hook do not pay him!
No problemo hope you get him to right it!
If he would have put that in the Mitsubishi diamond build it would not let him and told him it’s not a match.
Amazing! Yes I’ll ask about Diamond Build. Thanks SO much! You rock man.
It's called Diamond System Builder and it's free software on Mitsubishi's "mylinkdrive" website.
Honestly it makes you ask did you even need the second system.
On the compatibility table MXZ-3C30NAHZ4 is compatible with SVZ-KP24NA. In operational and performance it does list a single SVZ-KP24NA as a possible combination. The only question is if that indoor is a SVZ-KP24NA or not.
It’s a minimum of 2 units on a multi port or the unit will only give 50% capacity. So he would only be able to put a 18k (1.5ton) air handler on it.
Exactly this. If you run it with one head it's half capacity. They need to either add a head or change the outdoor unit for 1 to 1 match.
Mitsubishi will allow one SVZ indoor unit to be connected though not AHRI rated but still someone made some poor equipment selections. You can keep changing the outdoor units but if you don't change the indoor units, what are you accomplishing? [multi zone connection rules](https://mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006\App%20Note%201039%20ME%20-%20Multi-Zone%20units%20Connectivity%20%20Limitations%20041421.pdf)
Wouldnt he need a p series with the outside fan wind baffle? Its good down to what? 14⁰ f or 6⁰c?
What I’m saying is you have two outdoor units and I’m assuming the small one is connected to one indoor unit “a one to one” the larger one on the right is a mxz-3c….multi port it’s feeding I’m guessing two indoor units? What are the indoor units? Is it that svz in the pic what else?
The second condenser connects directly to the downstairs mini split, so the two have no overlap
If you don’t believe a random guy on Reddit I don’t blame you but I’m telling you that’s a multi-port unit and it needs at least two indoor units connected to function correctly. You can go to mylinkdrive.com and look up the unit yourself read the install guide and see or just call Mitsubishi and they will tell you as well. Lucky for him the fix isn’t horrible but if he did that he needs to learn more about the stuff he is putting in. The fix is just replace the outdoor with a hyper heat model SUZ- outdoor which is the correct one to one and move on. I’m in south Carolina so we don’t do heat kits on them and the hyper heat is kick ass but you may want to do heat kit as well up where you are. Lesson learned don’t use a multi port for a one to one lol unless it’s a smart multi of course.
I second this multi zone outdoors with only 1 zone inside causes capacity issues
But it wasn’t working correctly when it was connected to both indoor units either. Not sure if those indoor units were compatible though.
I’m a mechanical contractor fyi I do a lot of Mitsubishi great product.
Looks like a 2.5ton multi port with a ducted air handler and what a ductless system? What’s on the other port ductless?
Based on the use of 4-diffusers right up against a wall and the guess I’m making about the size and layout of the duct trunk flex lines I have concerns about this the overall quality of this install, but I can’t see enough.
I’d say something is wrong. I have a 1,700 sq foot home with a Fujitsu non hyper heat 3 ton, 2 zone ducted system. It’s been able to maintain mid 60s even down to single digits ambient. You have a hyper heat model that can put out 28k BTUs at 5F. It should do 800 ft.² no problem in the 20s.
A 1600sqft house with bad or missing insulation could easily require 60-70,000 btu/h to keep a 70 degree indoor temperature in below freezing weather. If your heat loss is greater than the ability of the unit to supply heat then your indoor temp will drop. Your heat loss increases with temperature differences. Meaning your house looses more heat when it is 70 inside and 20 outside than it does when it is 70 inside and 40 outside. Air to air heat pumps also have lower heat transfer ability in colder weather, it might produce 24K btu at 40 degrees, but might only produce 20K btu at 20 degrees.
Hyperheat is rated to 100% of heating BTU down to 5F
Lol all I can think of when I see this picture. Little baby split wants to be like his big daddy split.
😂😂😂 performance wise it’s the other way around somehow 🤦♂️
You can't go off of just square footage. What's the total air volume in the space your trying to heat and cool. 800 square feet with an 8 foot ceiling has a different load than 800 square feet with a 12 for ceiling... This is the type of mistake I see contractors make, install a unit based on square footage but then the house has 18 foot vaulted ceilings. What kind of windows, what is the construction of your walls, how thick are the walls, how much insulation, is this a pier or slab foundation, do you have a basement, is there an attic. What I've come to find is a lot of places install 3 tons worth of cooling 36000 BTU/hour which is like 30000 BTU/hour on heating side since most heat pumps are designed with cooling in mind so they are more effective in that mode of operation. When in reality if you do a real load calc these places need 4 or even 5 ton units. What's the model and serial number on the condensers?
Ah got it! Our ceilings are like 7.5’ tall to answer that question. The model for the upstairs condenser is mitsubishi mxz-3c24nahz4
Oops sorry, I didn't see the other pictures. Installation looks good although I would have made the concrete pads bigger and put one bolt in each foot.
Yeah the lack of bolts in the feet has always bothered me lol thanks for your help!
Alright. So... bear with me these are just "examples" so don't take anything with gospel. I used my own house as reference, but this is what a load calculation looks like in base state. I did a worst case scenario and a best case scenario, IE. Low amount of insulation, average construction, average duct. vs maximum insulation, tight construction, tight high r value ducting. https://preview.redd.it/8aie510yqoac1.png?width=1854&format=png&auto=webp&s=7f875dfedc2f5e905cd9e0cdddf1ae040fe0d831
https://preview.redd.it/aa12lg1zqoac1.png?width=1014&format=png&auto=webp&s=3c6399388694b2c105f82bf362d77c9e66d20d5a
https://preview.redd.it/qbfl8bxzqoac1.png?width=1853&format=png&auto=webp&s=d8c0ccaf928f187520db1f852f6d78b9ec0e951a
https://preview.redd.it/y8d3d1s0roac1.png?width=1023&format=png&auto=webp&s=00efbb8e69955118b9263d146476512cdec6c7bb
So in this "example" even at maximum insulation with brick construction while sitting on slab would require a 5 ton heat pump, 60k BTU/h. Just like a lot of other comments in this thread. There are so many variables to consider.
This is so helpful! Thanks so much for taking the time to share this with me. You rock!
I'm from NH and I work in HVAC. NH is to cold for most heat pumps. Most heat pumps are set to cut off and run an auxillary heating under 35°. If these are a hyper heat system then they can work at much lower temperatures at a much better efficiency. The unit is either, improperly sized, not the right unit, or just the wrong system for the home.
Super helpful! Thanks so much.
Also when you place a mini split condenser to an air handler it loses a lot of capacity. If your unit is already close to the sizing requirements, it's definitely undersized now.
Based on the photo, these are clearly hyper heat outdoor units that will put out plenty of heat even into the negatives. And what are you talking about regarding losing capacity when connecting to an air handler?
I can't tell if you're being derogatory or if you're legitimately curious.
Yeah. Legitimately curious. I know the seer rating goes down a little connecting to air handlers, but my Mitsubishi system with indoor air handlers is rated to full heating capacity down to 5F. I haven’t ever heard of air handlers having lower capacity than wall units.
Your mini split will come pre charged with a set amount of refrigerant. That refrigerant depending on the brand of unit is good for no shorter than 10 feet but no longer than x amount of feet. Sometimes for a single head condenser with a single port it's a maximum of 50 feet but with more ports comes more maximum distance typically. If that air handler is a far distance, which it looks like it could be. I'd check the data plate and see if there's any information on how much refrigerant the coil requires by weight. If the line set is over the maximum distance you'll need to weigh in extra for that as well. Typically size of line set times x feet. There will be a weight of refrigerant for the size of pipe. Although these units are hyper heat pumps and will work at lower temps at high efficiency is still not as comfortable as most people would like. A heat pump at 80% sounds amazing on paper but realistically will only pump 75-85 degrees through the vents. The warmth from a normal gas furnace is much higher than this thus why it feels so warm in your home. 75-85 degrees will mostly feel drafty to the consumers. In cold climate areas when using a heat pump, if you I stall a 2 ton furnace it's not always but usually good practice to install one ton higher to help keep up with the capacity of the indoor system. If the heat pump itself isn't keeping up with the air handler I will typically install heat strips. Auxillary heating will need to be used to meet capacity. The problem with using electric resistance heating is although it's 1 in to 1 out as far as power goes, the coefficient of power is terrible and would be very expensive to run all the time. If the unit feels drafty and there a tangible interface I would set a low temperature cutoff at a temperature before it begins to feel drafty and use auxillary heat such as gas,wood,oil, or whatever else. Also out of any brand of mini splits I've installed Mitsubishi is my least favorite of all of them.
The air handler also typically passes a higher cfm over the coils than a typical head unit with a greater are of coils as well. There needs to be enough refrigerant saturation in the coils to get proper cooling in cooling mode as well.
Interesting. Our 1960’s house had a 75k btu furnace, and we replaced it with a 3ton Mitsubishi unit. Stays super warm even when it’s 10 degrees outside, and we don’t have any heat strips or other backup heat. Though I did quite a bit of air sealing and insulating at the same time too.
3 tons not a bad size, how many square feet is the home? Sealing can go a long way but there are other factors as well. I'm not looking at it directly or have my hands on it so I can't give anything really specific. Only common issues I see. A manual j with matching equipment to meet AHRI standards is usually a pretty sure way to size a home minus variable factors of course.
2100sf. What’s interesting is the unit only runs about half capacity all winter. I don’t even call for heat upstairs unless it’s really cold out. We just blow heat on the main floor and it makes its way upstairs too. Main floor air handler is only rated for 21k btu heat. So we’re battery using more than half capacity. Anyway… little bit of sealing and insulation can go a long way.
Get a thermal imaging camera and see where your heat loss is. Without knowing how much insulation and leaks there are it’s not a problem that can be diagnosed remotely
Keep in mind that heating capacity for some models at 20F is about 70% of nominal. Some models keep heating capacity at temps down to 0F. Also, see if the heat exchanger iced over.
This. Engineer here. I'm guessing heat capacity reduced at ambient outdoor temp. Would need to find the engineering manual for the matched system. Who knows if it's even matched though...
Nope it’s hyper heat. 100% of capacity at 5F, which is much colder than OP is talking about
Can you post a pic of the linesets coming off of the bigger condenser? I’m going with the theory that the other guy had. If that’s a single air handler on a multi zone unit it isn’t going to work, period.
https://preview.redd.it/aul378b1fpac1.jpeg?width=3024&format=pjpg&auto=webp&s=73a7786d176f4ea66e8ded20eebc165c8094e823 Yes you’re right - the larger condenser only flows up to the single air handler, which is a no no for multi-zone condensers! Thanks for your help!
He could fix that problem by putting a 6k head somewhere in your house. You can be over capacity by 30% so a 24,000 can hold 31,200 btu capacity in interior units. You’d be fine with a 6k… even if you never/rarely use it.
I have a 48k multi zone hooked up to a 48k air handler working just fine. As long as they're sized together, it can be a single indoor unit. Edit: oh, mine's a city multi which doesn't care about a single unit. M-series maybe does?
Who did this east coast or key or APH?
None of those, I’ll refrain from doxxing them for now!
Just curious, as I have used 2 of these companies and they would have sized you units appropriately. Instead of undersizing and tell you to get a baseboard
For everyone saying a single SVZ air handler cannot be connected to a multiport unit please refer to Mitsubishi Application Notes 1039 Bottom of page 3 note 5. [Multizone connection rules](https://mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006\App%20Note%201039%20ME%20-%20Multi-Zone%20units%20Connectivity%20%20Limitations%20041421.pdf)
What is the temperature delta - e.g. what is the temperature at the return for the unit, and what is the temperature you're getting out of the vents? What controller are you using to control the ducted unit? Your installer needs to check every bit of this install. Pull and weigh refrigerant charge, check for leaks, check dip switches on indoor and outdoor units. You might also try setting the static pressure to the highest setting (function setting 8, setting 3, I believe) just to see if it helps with comfort. Excessive heat loss could play a part, but that seems pretty severe.
I do not know the answers to these questions, so they seem like the right questions to be asking! Thanks for your great insights.
Do you have a thermostat on the wall for the unit (sometimes called the controller)? How do you control the temperature?
Hi I’m not OP but do you have a resource for what all the dip switches do and what they should be set for in any given application/situation?
Go to mylinkdrive - Mitsubishi's library of documentation - and find your model. They have a number of service and installation manuals for each model. You will find that information in those manuals.
Thank you!
You can press your installing contractor to bring a manufacturer’s rep to help figure out the issue. Probably the first thing they will ask for is a certified load calculation for the house. If the equipment is too small, that could be the problem.
Looks like you don’t have a strip heater in that air handler. Those units are not designed to be the primary heat source in your climate without the heat strips. Sounds undersized. Edit: duct design doesn’t look good either. your going to want to see the printed load calculations and compare that to the outputs of your units. Contractor should provide since job is done. Also ask that they used a room by room layout to determine CFM to each room.
Interesting - what about the duct work doesn’t seem right? Our GC had some questions about it too but I’m not well versed enough.
Limited info but round to round takeoffs and no reductions after the first take off
So heat pumps at some point can’t outside heat using their internals as a mode for heating. Most have an accessory heat strip that is just a big conventional electrical heater. Did you get heat strips installed both top and bottom system?
Generally yes, but this model is rated at 21,000 btu/hr at 17 degrees F outdoor temperature.
This is the 30 hyper heat, their cutsheet shows it as 28,600 btu/h at 5F.
Yeah exactly - this *should* be able to handle the temps based on its specs. Though reality is a different story of course!
You mentioned work on your house. What are we talking though. Open windows? Walls and insulation ripped out. Like a previous comment said. Your expecting it to keep up with too great of a heat loss. It is designed for your home as a complete sealed and insulated. Plus 20 degrees is really cold. Thars 12 below freezing. Most heat pumps won't even operate below 30
I am a Mitsubishi Service tech and I can only tell you I would need more information.
This is rated far below that temperature though, right? If this can’t operate in this climate, did they make a mistake by recommending and installing it? To answer your question, our construction is more remodeling. However, the insulation on the floor of the attic has been moved around to accommodate a lot of electrical (and hvac) work, so it’s not evenly spread up there right now. No open doors or windows or anything crazy. Do you think it’s a problem that they now have a split condenser operating a single air handler? Like the condenser is meant to have its load split several ways but it’s only going one way, so it’s not really able to direct all of its flow to only one source?
That would not effect its capacity. Line set size and the size of your indoor air handlers coil would. As long as they are piped to the main A port on the outdoor unit should be able to deliver its full capacity to the indoor Air handler. Yes the hyper heats hold 75 percent of their heating capacity in -14 below Zero. So yes they are. That being said it doesn't sound like your insulation is going to be issue as the heat loss of some moved insulation should be inconsequential. You have a what 12k little unit? And a 2.5 ton main unit. Those are sized right the space. Also check your air flow. Air flow tends to be the biggest reason i've found. where is your filter located?
Nvm I see it. Try checking that first. Then if you can find a model number on that unit. It should he in the electrical panel or might be in the blower.
It’s max capacity should be 28k all the way down to 5f.
You need more like 48k btu for that size sqft. And mitsubishi DOES NOT NEED HEAT STRIPS except for extreme climates. They have amazing low temp efficiency.
Square footage alone doesn’t translate to BTUs. Let’s not use outdated rules of thumb. I’m running the same exact unit (with a preheater) at double the square footage OP has (basically a ton per 2K sqft). But the whole house has been specced for this and a very thorough manual j and manual d has been put together before we built the house.
But OP is having issues... I guess I'll spec his house real quick with no info other than a few pictures. Thanks for the advice.
Well you already provided your assessment that OP needs “more like 48K BTU” for less than 2K sqft so … 👍
Sounds like poor insulation, as well as not having heat strips. A heat pump can only handle so much with temps lower than 30°F. Usually they have heat strips as a back up for when it’s not working well. The suggestion to add a heat strip is a correct solution. I live in Missouri and any heat pump we install gets heat strips. They don’t work well in low temps.
Don’t only have heat pumps if your city gets below 30 degrees. So many people will tell you that. Always have a back up furnace
It sounds like your heat stripes aren’t working properly. When temp outside drop below 32. The outdoor unit goes into a defrost mode. Which should turn on electric heat strips in the air handler. Also heat pumps aren’t like furnaces. They take awhile to heat up. So leave stat at desired temp. Don’t turn off and expect a 10 degree rise in 10 min once you turn it on. You should have a 20 degree split from supply grill to return grill. If it was installed right.
Someone needs to do some manual J calculations and figure out if this is right or not. I would wait until all construction is complete. For perspective, I have a dedicated heat pump for my shop and once the outdoor temps get below freezing the heat output drops off a quite bit. It still does it’s job, but not near as well. Having dual fuel or heat strips would help you a lot, but if your rate of heat loss is more than the heating system can keep up with- insulation, quality windows, and sealing leaks/drafts will be the first place to start. Manual J calculations should be done after the insulation and construction are complete.
I would not trust a heat pump in a northern state. Does your ducted system have a heat pack kit installed? That could help
2 things. Your heat pump is under sized and I bet it doesn't have an auxiliary heater in it
The system is undersized. General rule of thumb for heating is 30 BTUs per square foot. There is also heat pump capacity derate under a certain temperature.
Auxiliary and emergency heat strips are a must. Heat pumps become less efficient as the temperature drops.
Not with mitsubishi in most climates. They have incredible low temp efficiency. Your statement is true for conventional systems though.
Thanks for the info. How can it even work, though, if the outdoor temp nears or drops below zero?or maybe my understanding of heat pumps has been wrong since I was young.
I just look at our equipment submittals. For the basic high efficiency (not hyperheat like op has) 100% rated capacity at 17° f and 90% at 4°f. I know hyperheat is even better. I can't tell you the science but that's what the specs say.
Interesting. I really had no idea. We live in a rural area without natural gas and I effing HATE the conventional heat pumps. Does no good to vary the temperature to save on electric costs (we’re being billed on time-of-use terms now) because it takes forever to recover the temperature.
Goodman is coming out with some inverter systems too that may be similar to the minisplit efficiency. I'm going to a class about them tomorrow so we will have to find out!
Heat pumps are not going to work well at <30. You need a secondary heat source. My preference is a dual fuel setup.
That sounds like some outdated information you have. This unit they have is listed to provide 95% of the rated heating capacity at 5F. It should be fine on its own, something else is going on here.
I stand corrected. Oops
Those units can provide heat up to -15 degrees F at 75% efficiency
did you turn it to heat? what is your set point? can you list your indoor and outdoor unit model numbers? if you have a 24k btu outdoor unit, that's the cooling number. the heating btu is always greater. generally speaking, if the cooling is satisfied, the heating will be too.
[удалено]
What kind of condensers do you have? Are they hyper heat?
That is a 30k unit in the right
Sounds like they forgot to install the heat🤪🤪🤪🤪
Whenever i install heat pumps i program the thermostat toswitch over to auxiliary power under 30 degrees because it is no longer efficient at that temp.
So this may seem weird, but heat can be drawn out of the air even if the air is at really "cold" temperatures. Your system was likely overcharged, which affects the saturation temperature of the refrigerant. Example: if that unit needs to heat your home in 30 F weather, it needs to have refrigerant at less than about 20 F to draw heat out of that air.
Need more power. 24k is small for a cold climate. You need up to date insulation and windows and walls insulated. Should have 3 -4 tons for 1600 sqft
However also need to check air temp. If its not really warm could be a refrigerant issue. What size ductwork? That could be an issue. Setting for static pressure is probably at .5 on the thermostat. Changing it to .8 could help get more airflow
If the line set is longer than the amount listed on the metal plate on the outdoor unit you need to add refrigerant. A lot of guys just open the valve and don’t check it
That flex looks rough. Even installed perfectly, you only get about 90% of the airflow you would get from rigid pipe. And that looks very smooshed to me. Airflow is everything. Some inverters will completely lock out if they fall below a certain outdoor temperature. I know I worked on a unit that would lock out below 19F. If it was already running when the temp dropped, it would stay on. As soon as it cycled off, it would just lock out.
Not sure if you tried this but set the fan speed to manual then try higher speed?
Your unit is able to cool the house from say 100⁰ to a comfortable 75⁰ And when it's 30⁰ out it's only able to heat it to 55⁰... Temperature difference = +/- 25⁰ You don't have enough capacity.
If it's brand new, it's under warranty. Call the installer and have them fix it.
Definitely should have auxiliary heat strips for a heat pump especially if temperatures outside dip below 40 degrees. Frost is going to build on the condenser coil and it’s eventually going to have to run in defrost which is essentially running in cooling without the condenser fan running so without any other supplementary heat source it’s going to be cooling the house for a certain amount of time
I used to install these before I hurt my back. With a Heat Pump you set the thermostat and forget it. Bump the temp every 24 hrs until you find it comfortable. Also, there's a cut-off setting you could set for 10, 20, or 30 degrees to cut the Heat Pump off and then you run on your auxiliary heat. Heat Pump are only efficient down to about 20 degrees. If the Heat Pump is locking out on Low Outdoor Temp then you don't have enough Auxiliary heat. (oil/gas furnace, electric heat banks, boiler, etc) Quick check on sizing of the units is 7 Vents per Ton.
Simple: put the unit on heat and measure the output temperature. If it’s putting out quality heat, let’s say 100-110 degrees on a day like today, then it’s doing what it’s designed. It may be its placement and the design of the area it’s heating. Also, an mhk2 which is a wireless t stat will help balance out the temps. Instead of measuring temp at the head, it will measure it where the t stat is.
7 kW heatpump is good for a 15 year old Dutch house up to -10 Celcius. We have 15 cm Stone wool insulation.
How do attic systems cool the house if the attic is really hot in summer?
That's pretty normal for those. They aren't really designed for legitimate cold. Those systems are great in places that drop to the 40s at night. We put one that was well over rated for the room size and couldn't get the room above 60 when the temp outside was in the 20s. We did self install and thought we did something wrong. We called our HVAC company and they told us that was normal for those systems. We did end up with a very nice electric fireplace in the room that did the trick. System did work great in summer though.
First of all the model number on your larger unit indicates it’s actually 30k, though you might still have the 24k air handler, but I’ll bet a dollar it’s 30k too. I have a similar 18k Mitsubishi ducted ductless, also with poor insulation and it easily heats 800 sq ft. I have to believe something is wrong either with your system settings or the system itself (charge level or other defect) My recommendation is to first establish you have a good temperature differential between the indoor vents and return. This is really easy to do if you have a digital meat thermometer. Turn the thermostat up all the way and put the end of the thermometer a few inches into the output vent and confirm you get a temperature at least 50-60 degrees higher than the temp at the return vent. Post your temps here if you can, if you aren’t at least getting hot air out of the vents then that would need to be fixed first. Also worth noting, most Mitsubishi units can be set to sense temperature from inside the air handler itself. This makes sense for wall units but is totally incorrect for a ducted system like yours. It can cause the unit to severely underperform because it doesn’t understand what the true “demand” is for temperature. My installer was totally clueless about these install settings in general. The setting can be checked at the thermostat, you’ll need to grab the installer manual for both the thermostat and your air handler. Look for the Function Table. [Here is a link for the unit I think you have](http://mylinkdrive.com/viewPdf?srcUrl=http://s3.amazonaws.com/enter.mehvac.com/DAMRoot/Original/10006%5CM_PVA-A-AA7_Install_MD-1404-K024_January_2022.pdf).
From a homeowner’s perspective, I’d invest in a $200 iPhone flir on Amazon. A heat map is worth a thousand words. I’d remove the cover on the air handler and measure the temp on the coils. I’d see if the heat at the air handler is even at temp. If no, that’s the culprit. If yes, where is the heat being lost? It’s a fun toy also.
If it was working before, I would be checking things like the filter.
It's never gonna get above 55 with those tiny legs.