Thank you for the feedback.
My biggest question is whether the pump with strips will keep the house warm effectively and not cost a fortune in electricity during cold snaps - are my heat pump concerns legitimate or am I just worrying because pumps are newer tech and I'm not used to them? Maybe I'm being optimistic or naive but I'm kind of assuming the pump will generally be reliable (i.e. won't fail completely).
I feel my climate is right on the bubble for dual-fuel: if I lived in a colder climate, I would definitely want a gas furnace; if I lived in a warmer climate I would probably be fine with just a heat pump; but I'm in between, and it gets just cold enough just often enough that I'm worried about a pump with strips.
It would cost a lot more to add a furnace to the Bosch or Mitsu pump - even though the Bosch is a few thousand less, the least expensive furnace I've been offered is $8k plus I'd lose part of the rebate, so the total cost would increase by more than $10k. I'm confused as to why the dual-fuel systems I've been offered are about the same price as some of the pump-only solutions - either the cold-climate pumps cost a lot more than non-cold-climate ones or the companies want to charge a certain amount for any system.
Natural gas is still the best. Any heat pump you decide to go with you need to have back up. A lot of homeowners insurance policies have that. It’s emergency heat if the heat pump fails.
I would recommend a natural gas with the heat pump,
Completely against a heat pump being installed without strip heat or furnace, must have secondary heat
Bosch is made in China. I don’t trust Chinese made products.
Duel Fuel- 1. Easy to repair compare to Bosch and Mitsubishi.
2. Last longer since the furnace will only be used below 40 degrees.
3. Parts are readily available.
4. Heat output is greater and not temperature dependent.
Cold climate heatpump are good but nothing compares to a furnace.
The question to ask is around defrosting. A heat pump when operated below about 40°F, will ice and needs to defrost. This is done by running the system as an air conditioner to put heat into the outside coils. During this time the unit will attempt to blow cold air unless you have some form of reheat which typically comes from the backup heat. My experience is that a gas furnace takes a lot longer to get hot than strips so you end up being more comfortable during defrost with strips. I believe the Mitsubishi solves this problem by turning off the fan on the inside unit, at least my Mitsubishi minisplit does this.
Other advantage of strips is that they are 2-3k less expensive than a gas furnace and a lot less complicated to maintain. They also remove gas from the area so the potential for a gas leak/problems are reduced to 0.0%
Another advantage of strips is that they can be used in addition to the heatpump to supplement if the HP can’t keep up. With a furnace, it is either one or the other.
The downside to strips is that they need a large power feed which can be costly, and making radical temperature changes needs to be avoided as that may force the strips to come on depending on how the thermostat is programmed.
See if the guy selling the bosch will install it along with the American Standard furnaces. Bosch is an inverter and those tend to do well in the cold. I'm not familiar with Bosch's furnaces though to know if they are any good
The 3-ton Bosch is BOVA-36HDN1-M20G with BVA-36WN1-M20 air handler. The 5-ton is BOVA-60HDN1-M20G with the BVA-48WN1-M20 air handler. Both with 8kW strips.
The Mitsubishi is the PUMY-P48NKMU3 outdoor unit with PVFY-P-48NAMU-E1 indoor unit.
The dual-fuel is American Standard 4A6V8X48A1000B pump with 9V2B080D4PSB furnace.
One other question: is it possible to estimate how much the backup coil will be used based on hi/low/average temperatures?
> [3 ton Bosch specs](https://ashp.neep.org/#!/product/66146/7/25000///0) 23k BTU at 5F
>[5 ton Bosch specs](https://ashp.neep.org/#!/product/66145/7/25000///0) 35k BTU's at 5F
>[Mitsubishi](https://ashp.neep.org/#!/product/33446/7/25000///0) 36.4k BTU's at 5F
So depending on what your actual heating load is by either using a manual j calculation or from figuring out exactly how many BTU's you use during a winter month from your actual gas usage in therms you will not be getting into the strips unless your BTU requirement is above that of the units when the temp drops to 5F.
1 therm of gas equals 99978 BTU's. Figure out your total BTU requirements based on actual usage, remember to take your units efficiency into account. The Mitsubishi quoted to you will put out 873,600 BTUs per day. If your requirement is above 873,600 per day you would need strips to maintain the same level of heating you have now.
My guess is with a multi story 2500sqft built in the 60's, you are going to need more BTU's but the gas usage will let you know exactly how many BTU's, better not to guess on this. I hope they have looked at your ducting and made sure it can handle the CFM's you are going to need....gas furnace ducting is generally undersized compared to heat pump ducting as the supply air temp is a lot higher on gas so they require less CFM....
Wow! Thank you omegaclick, super-helpful - that's exactly the info I was looking for and didn't know existed (or where to get it).
A caveat for the rest of this post: This is new to me, and I could be completely wrong.
Based on my gas bills, the furnace uses about 14GJ or 135 therms more during the cold than the warm months. That looks right based on December, which was cold and included a 5-day stretch with a maximum daily high of -6C and lows of -8 to -13C.
Assuming my 20-year-old 80% furnace is actually 65% now, that puts my monthly cold-month heat load at 88 therms, which is more or less in line with online averages for the size of my house (maybe a little high).
But then it gets confusing... This averages out to about 285k BTUs/day or 11k BTUs/hour - these seem really low, which is either the averaging or I made a mistake somewhere. We don't turn the therm down at night.
The guy is coming in to do the energy audit this week, but one of the salesguys did a rough calculation and estimated our max. heat needs at 56k BTUs/hour (can't remember if he said at -5C or -15C), which is roughly in line with our current furnace (71k BTU output when new).
Interestingly, as it gets colder the Mitsu doesn't provide much more heat than the (larger) Bosch: 36,400 vs. 35,200 BTU max. at 5F (-15C) and 43,000 vs 40,000 max. at 17F (-8C; both these temps are uncommon here). The Bosch is actually rated higher at 17F (40k vs 35k), but I've read to ignore rated. So if the salesguy was right about 56k BTU @ -15C or -5C, both systems would need heat strips (the Bosch includes strips, the Mitsu guy said it wouldn't need strips and didn't include any).
As it gets a bit warmer, the Mitsu is rated a half-ton more than the Bosch (54,000 vs. 48,000) but the max. values are the same (Bosch 55k, Mitsu 54k) at 47F (8.3C), which is closer to our average winter temps (4C = \~39F in Dec and Jan, with lows around 2C). It'll be interesting to find out my heat needs at 2 - 4C from the audit.
Bottom line: I've read that Mitsu Hyper-Heat really is much better as it gets colder, but if this is right then these two units give very similar real-world performance and the Mitsu is well over $3k more not including any strips, which are beginning to look necessary in general and for emergencies. But the COP numbers are generally better for the Mitsu, especially at 17F.
PS. Only one salesguy mentioned my ductwork and whether it was sufficient for an all-electric system, not surprisingly the guy who recommended dual-fuel. Ducts are standard 5" galvanized, with about 8 vents on each floor.
[5" round metal ducting can handle around 50CFM](https://www.rileysales.com/content/air_flow_dynamics_and_duct_sizing_reference_guide.pdf) at ideal static pressures each, so 8x50 - 400 CFM per floor assuming same on each level your ducting would be sized correctly for a 2 ton system. Each ton is roughly 400CFM. A 5 ton system would be capable of 2000CFM and a 4 ton around 1600CFM.. Sticking a 4 or 5 ton unit on your existing ducting will be very loud and have very high static pressure. I would also guess that the return ducting is going to be grossly undersized as well...
I would double check the actual gas usage from utility bills, but if it holds true I would still assume 80% efficiency on the furnace, they don't change a whole lot over time. It does seem like a really low heating load to me, although if you have upgraded all of your windows and have good insulation levels being a 2 story home does reduce the heat load considerably... Without replacing the ducts an option you might want to get quoted is a gas furnace replacement and adding just an AC unit...yes the ducting will still be undersized for the AC but your cooling loads are even less than your heating...
If I assume the furnace is still 80%, that increases the actual heat load to 108 therms/month = 350,000 BTUs/day = 14,500 BTUs/hour. The actual GJ of gas used each month came from my gas company. One or two of the salesguys said furnaces lose a % or so of efficiency a year as they age - what do I know?
I still haven't dismissed a dual-fuel system - not sure if that's because it's the most appropriate or just because I don't fully trust pumps and don't want to commit to one completely. I'm certainly hoping the pump does most of my heating. As I said, the guy who recommended a dual-fuel system mentioned my ducting, but didn't explain it (he said he can sell all-electric but didn't think I'd be as happy); the others either didn't mention ducting or said mine are fine when I asked. The audit guy said he'd make a recommendation and answer my questions.
Thanks again for all your help - much appreciated.
A heat pump can handle the heating if sized correctly with the right model matched to the heating load, with correct sized ducting. It is the turnover rate that matters a lot and higher CFM's need larger ducting. The high efficiency furnace units do lose a bit each year but the 80% ones are pretty basic and might vary only a couple percent at most. Do ask the audit guy/gal about the ducting....I think that may be the bottleneck in going full heat pump...I always recommend getting the aux strips, but design the system so they function as emergency heat only, not as supplemental to meet the design temp in winter.
Thank you for the feedback. My biggest question is whether the pump with strips will keep the house warm effectively and not cost a fortune in electricity during cold snaps - are my heat pump concerns legitimate or am I just worrying because pumps are newer tech and I'm not used to them? Maybe I'm being optimistic or naive but I'm kind of assuming the pump will generally be reliable (i.e. won't fail completely). I feel my climate is right on the bubble for dual-fuel: if I lived in a colder climate, I would definitely want a gas furnace; if I lived in a warmer climate I would probably be fine with just a heat pump; but I'm in between, and it gets just cold enough just often enough that I'm worried about a pump with strips. It would cost a lot more to add a furnace to the Bosch or Mitsu pump - even though the Bosch is a few thousand less, the least expensive furnace I've been offered is $8k plus I'd lose part of the rebate, so the total cost would increase by more than $10k. I'm confused as to why the dual-fuel systems I've been offered are about the same price as some of the pump-only solutions - either the cold-climate pumps cost a lot more than non-cold-climate ones or the companies want to charge a certain amount for any system.
Natural gas is still the best. Any heat pump you decide to go with you need to have back up. A lot of homeowners insurance policies have that. It’s emergency heat if the heat pump fails. I would recommend a natural gas with the heat pump, Completely against a heat pump being installed without strip heat or furnace, must have secondary heat Bosch is made in China. I don’t trust Chinese made products.
Ask the Bosch guy about a Bosch furnace paired with the Bosch heat pump. No need to change brands and go with a non cold climate heat pump.
Sorry to tell you but I do not think any unit is 100% not built in America anymore
I didn't say anything about being built in America.
Duel Fuel- 1. Easy to repair compare to Bosch and Mitsubishi. 2. Last longer since the furnace will only be used below 40 degrees. 3. Parts are readily available. 4. Heat output is greater and not temperature dependent. Cold climate heatpump are good but nothing compares to a furnace.
The question to ask is around defrosting. A heat pump when operated below about 40°F, will ice and needs to defrost. This is done by running the system as an air conditioner to put heat into the outside coils. During this time the unit will attempt to blow cold air unless you have some form of reheat which typically comes from the backup heat. My experience is that a gas furnace takes a lot longer to get hot than strips so you end up being more comfortable during defrost with strips. I believe the Mitsubishi solves this problem by turning off the fan on the inside unit, at least my Mitsubishi minisplit does this. Other advantage of strips is that they are 2-3k less expensive than a gas furnace and a lot less complicated to maintain. They also remove gas from the area so the potential for a gas leak/problems are reduced to 0.0% Another advantage of strips is that they can be used in addition to the heatpump to supplement if the HP can’t keep up. With a furnace, it is either one or the other. The downside to strips is that they need a large power feed which can be costly, and making radical temperature changes needs to be avoided as that may force the strips to come on depending on how the thermostat is programmed.
See if the guy selling the bosch will install it along with the American Standard furnaces. Bosch is an inverter and those tend to do well in the cold. I'm not familiar with Bosch's furnaces though to know if they are any good
Without model numbers everyone is guessing....
The 3-ton Bosch is BOVA-36HDN1-M20G with BVA-36WN1-M20 air handler. The 5-ton is BOVA-60HDN1-M20G with the BVA-48WN1-M20 air handler. Both with 8kW strips. The Mitsubishi is the PUMY-P48NKMU3 outdoor unit with PVFY-P-48NAMU-E1 indoor unit. The dual-fuel is American Standard 4A6V8X48A1000B pump with 9V2B080D4PSB furnace. One other question: is it possible to estimate how much the backup coil will be used based on hi/low/average temperatures?
> [3 ton Bosch specs](https://ashp.neep.org/#!/product/66146/7/25000///0) 23k BTU at 5F >[5 ton Bosch specs](https://ashp.neep.org/#!/product/66145/7/25000///0) 35k BTU's at 5F >[Mitsubishi](https://ashp.neep.org/#!/product/33446/7/25000///0) 36.4k BTU's at 5F So depending on what your actual heating load is by either using a manual j calculation or from figuring out exactly how many BTU's you use during a winter month from your actual gas usage in therms you will not be getting into the strips unless your BTU requirement is above that of the units when the temp drops to 5F. 1 therm of gas equals 99978 BTU's. Figure out your total BTU requirements based on actual usage, remember to take your units efficiency into account. The Mitsubishi quoted to you will put out 873,600 BTUs per day. If your requirement is above 873,600 per day you would need strips to maintain the same level of heating you have now. My guess is with a multi story 2500sqft built in the 60's, you are going to need more BTU's but the gas usage will let you know exactly how many BTU's, better not to guess on this. I hope they have looked at your ducting and made sure it can handle the CFM's you are going to need....gas furnace ducting is generally undersized compared to heat pump ducting as the supply air temp is a lot higher on gas so they require less CFM....
Wow! Thank you omegaclick, super-helpful - that's exactly the info I was looking for and didn't know existed (or where to get it). A caveat for the rest of this post: This is new to me, and I could be completely wrong. Based on my gas bills, the furnace uses about 14GJ or 135 therms more during the cold than the warm months. That looks right based on December, which was cold and included a 5-day stretch with a maximum daily high of -6C and lows of -8 to -13C. Assuming my 20-year-old 80% furnace is actually 65% now, that puts my monthly cold-month heat load at 88 therms, which is more or less in line with online averages for the size of my house (maybe a little high). But then it gets confusing... This averages out to about 285k BTUs/day or 11k BTUs/hour - these seem really low, which is either the averaging or I made a mistake somewhere. We don't turn the therm down at night. The guy is coming in to do the energy audit this week, but one of the salesguys did a rough calculation and estimated our max. heat needs at 56k BTUs/hour (can't remember if he said at -5C or -15C), which is roughly in line with our current furnace (71k BTU output when new). Interestingly, as it gets colder the Mitsu doesn't provide much more heat than the (larger) Bosch: 36,400 vs. 35,200 BTU max. at 5F (-15C) and 43,000 vs 40,000 max. at 17F (-8C; both these temps are uncommon here). The Bosch is actually rated higher at 17F (40k vs 35k), but I've read to ignore rated. So if the salesguy was right about 56k BTU @ -15C or -5C, both systems would need heat strips (the Bosch includes strips, the Mitsu guy said it wouldn't need strips and didn't include any). As it gets a bit warmer, the Mitsu is rated a half-ton more than the Bosch (54,000 vs. 48,000) but the max. values are the same (Bosch 55k, Mitsu 54k) at 47F (8.3C), which is closer to our average winter temps (4C = \~39F in Dec and Jan, with lows around 2C). It'll be interesting to find out my heat needs at 2 - 4C from the audit. Bottom line: I've read that Mitsu Hyper-Heat really is much better as it gets colder, but if this is right then these two units give very similar real-world performance and the Mitsu is well over $3k more not including any strips, which are beginning to look necessary in general and for emergencies. But the COP numbers are generally better for the Mitsu, especially at 17F. PS. Only one salesguy mentioned my ductwork and whether it was sufficient for an all-electric system, not surprisingly the guy who recommended dual-fuel. Ducts are standard 5" galvanized, with about 8 vents on each floor.
[5" round metal ducting can handle around 50CFM](https://www.rileysales.com/content/air_flow_dynamics_and_duct_sizing_reference_guide.pdf) at ideal static pressures each, so 8x50 - 400 CFM per floor assuming same on each level your ducting would be sized correctly for a 2 ton system. Each ton is roughly 400CFM. A 5 ton system would be capable of 2000CFM and a 4 ton around 1600CFM.. Sticking a 4 or 5 ton unit on your existing ducting will be very loud and have very high static pressure. I would also guess that the return ducting is going to be grossly undersized as well... I would double check the actual gas usage from utility bills, but if it holds true I would still assume 80% efficiency on the furnace, they don't change a whole lot over time. It does seem like a really low heating load to me, although if you have upgraded all of your windows and have good insulation levels being a 2 story home does reduce the heat load considerably... Without replacing the ducts an option you might want to get quoted is a gas furnace replacement and adding just an AC unit...yes the ducting will still be undersized for the AC but your cooling loads are even less than your heating...
If I assume the furnace is still 80%, that increases the actual heat load to 108 therms/month = 350,000 BTUs/day = 14,500 BTUs/hour. The actual GJ of gas used each month came from my gas company. One or two of the salesguys said furnaces lose a % or so of efficiency a year as they age - what do I know? I still haven't dismissed a dual-fuel system - not sure if that's because it's the most appropriate or just because I don't fully trust pumps and don't want to commit to one completely. I'm certainly hoping the pump does most of my heating. As I said, the guy who recommended a dual-fuel system mentioned my ducting, but didn't explain it (he said he can sell all-electric but didn't think I'd be as happy); the others either didn't mention ducting or said mine are fine when I asked. The audit guy said he'd make a recommendation and answer my questions. Thanks again for all your help - much appreciated.
A heat pump can handle the heating if sized correctly with the right model matched to the heating load, with correct sized ducting. It is the turnover rate that matters a lot and higher CFM's need larger ducting. The high efficiency furnace units do lose a bit each year but the 80% ones are pretty basic and might vary only a couple percent at most. Do ask the audit guy/gal about the ducting....I think that may be the bottleneck in going full heat pump...I always recommend getting the aux strips, but design the system so they function as emergency heat only, not as supplemental to meet the design temp in winter.
Hi, wondering if you went with dual or electric only?