Upgrading an old oil furnace and AC unit to a new high efficiency heat pump has been one of the two keys to making my family's home in PA produce more energy than it consumes (the other of course was adding a big fat solar array). Now that we've lived in the house for over a year I thought it would be a good time to look back at the data and see what sort of return on investment (ROI) this heat pump has given us.
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Alistair
2022-03-29 at 6:21 pm
I appreciated reading this article. I am currently looking at replacing oil heat and hot water ROI of a cold climate air source heat pump and standard electric heater. I factored in all savings I could, including reduced insurance, reduced maintenance and potential increase in home value to a buyer and came up with an ROI of about 11 years. (the upfront costs are very high, less a govt incentive). There are other non-tangible factors to consider too – reduced risk of catastrophic oil leak, savings from not having to replace the furnace in the future and of course, just the feel-good going green component. This is what I calculated in savings for my home in northern Ontario (we don’t currently use AC other than a small portable so this is just a guess)
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John Katerenchuk
2021-10-06 at 12:33 am
I enjoyed your article and analysis. It was timely as I live in Southeastern PA (Lancaster County) and the AC and Propane Furnace is approaching 20 year of age. I had been thinking about replacement of both with a heat pump but my experiences while living in Georgia on some cold days were not very positive as the heat pump on very cold days would not keep the house warm and comfortable. I was worried if that might also be the result in PA. I was also wondering if the investment would be financially viable compared to our actual cooling cost and propane heating cost. Any help you might provide would be appreciated to get me headed in the right direction.
Glad you liked it. Let me know what you pay for propane to fuel your existing furnace each year and I can get a better idea of how a heat pump would work financially for you (include both the total cost you pay to heat each year, how much propane that is, and the efficiency or AFUE rating of your existing furnace for a detailed answer). Even without that info I can say confidently that a heat pump will be able to heat your home just fine even on very cold days, because you live further South than me. I guess it’s possible that your home is bigger, leakier, and less well insulated than mine, but those are all problems that can be fixed, and if you read my net zero and profit post (https://profitgreenly.com/net-zero-and-profit/) you’ll see that my house is very far from being a Passive House and yet the heat pump still keeps us warm all by itself.
In terms of ROI a heat pump doesn’t cost much more than a stand-alone AC (particularly if you install it yourself). Mr. Money Mustache just wrote about doing a DIY heat pump install for just $4500 https://www.mrmoneymustache.com/2021/10/05/diy-heat-pump/. His unit isn’t quite as efficient as the one I got, but for $10,000 less I’m sure he’ll have a higher ROI.
Given that a heat pump can be over 400% efficient and a propane furnace can never surpass 100% efficiency, I think it’s likely that a heat pump will win out in the long term. Even if you burned propane in a generator at your house to power your heat pump you’d likely have a lower fuel cost across a whole winter than if you burned it purely for heat. Electricity prices are pretty low and stable here in PA so I don’t recommend doing this, it’s just an example. If you install solar on your roof you’re essentially locking in an electricity price till either those panels die (in 30+ years) or PA revokes our net metering law (I do expect this to happen eventually, but I bet they grandfather in existing installations). That means that the price to heat your home with a heat pump can be both very stable and very low. Propane on the other hand will likely fluctuation wildly in price in the near future (just look at Europe right now for an example of this) and so even if it happens to be cheaper now it likely won’t be over the long term (do send me your propane cost numbers from last year to check though, as I expect it’ll lose out to an efficient heat pump even now).
Here are the basics of my HVAC setup. Outside traditional AC unit. Approaching 20 years of age. Inside Propane furnace. Nordyne G6RC 080c-16B fed from a 500 gal buried Propane tank outside. Also approaching 20 years of age. Also, a Propane water heater that was replaced about 3 years ago.
I know the AC unit will need a full replacement next time if breaks down. The furnace has only required minimal yearly small service charges and replacement parts costs most of which I buy and do myself. I could not find any information on the furnace efficiency but on the manufacturers sticker it shows a input of 80,000 BTUH and a output of 73,000 BTUH. If that represents the efficiency then it would seem to be 91.2%.
Reviewing my Propane cost and usage back to 2007 on average for the furnace and the hot water heater I use 575 Gal/year. Cost swings all over the place depending upon year and time of year to fill the tank. The lowest is $1.02/Gal in 2016 and the highest is 2.52/Gal in 2014. My last fill was last month and that was $1.66/Gal. The average over the whole period is $1.65/Gal. So at the average price, my Propane cost per year is $950. At the lowest, it is $580 and the highest is $1450. I cannot tell how much of the Propane is used for Hot Water heating but I would think it would be no more than 10%. Additionally, in the equation, I need to think about the cost of replacing the inground 500 Gal propane tank. I am not sure of the lifetime of these tanks (it is approaching 20 years). It would be a shame to ignore this cost in the comparison analysis of heat pump/electric heating vs heat pump and Propane heating only to find the Propane tank needed to be replaced a couple of years later at a high cost.
Looking at the Electrical side it appears my bill increases by about $80 per month during the months when the AC is needed. Which is usually about 3 months per season. So roughly the AC costs about $250 per year.
I hope that provides you with the information you requested. From a cost analysis it comes down to comparing Heat Pump with Electric backup versus Heat Pump with Propane backup. I quickly looked at GeoThermal Heat pumps but the high up front cost would take more years to payback than we expect to be around in this house.
Thanks for the detailed info, and sorry for the slow reply. It looks like your furnace is more commonly sold as a Frigidaire FG6RC 080c-16B with a claimed AFUE of 92.1% so your division is about right. Sadly your having both a water heater and a furnace running on propane mean that I can’t be exact in my calculations, but using the standard assumption that the water heater uses 25% of your annual propane and the furnace uses the other 75%. That means You spend about $720/year fueling your furnace with 436 gallons of propane. A gallon of propane at 60 F contains 91,502 BTUs of energy so your 92% efficient furnace is turning these 460 gallons into 36,733,893 BTUs to heat your home over an average winter.
To get this same amount of heat from a heat pump you need to know its efficiency. Ground source heat pumps will give a single efficiency rating called a COP that they operate at pretty much all the time. A COP of 4 means 400% efficient. For air source heat pumps efficiency increases as the outdoor air temps increase, so they’re rated by HSPF which averages their efficiency across an estimated heating season. You can roughly convert HSPF to COP by multiplying it by 0.293, but the actual weather each winter will change your true efficiency year to year (climate change is likely to continue warming the world in the coming years so this efficiency will likely go up a bit over time). My heat pump has a 13 HSPF so it’s around 380% efficient. If I put 1 kWh into an electric resistance heater of 100% efficiency I get 3,412 BTUs out, so if I instead put it into my 380% efficient heat pump I get 12,966 BTUs out.
Dividing the 36,733,893 BTUs I calculated that it takes to heat your home by the 12,966 BTUs my heat pump creates from 1 kWh over an average winter I find that it’d take 2,833 kWh to heat your home with my heat pump. Well, there’s one more caveat. When it gets really cold my heat pump supplements its heating with electric resistance heat that’s only 100% efficient.
In 2020 I used 3,730 kWhs to power my heat pump for heating and another 546 kWhs to power my backup resistance heat on a few super cold days. A cheaper heat pump will use more backup heating, so let’s just add the full 546 kWhs I used last year to my estimate of 2,833 kWhs to heat you home. That’s still only 3,379 kWhs per year. With power costing around 10 cents per kWh in PA that would be only $338/year, far lower than the $720 you’re paying for propane! Installing solar dropped my $/kWh down to around $0.07 so with that your heating could cost only $236/year and that price would be locked in for the life of the heat pump (likely 15 years) unless PA scraps its existing net metering and SREC laws.
This isn’t a perfect prediction because there are still variables like what temperature your propane is actually delivered at (which changes how many BTU per gallon) and the exact temperature range your home experiences over a year. Your existing furnace also seems oversized for your home (a common problem in the US) and that could be reducing it’s efficiency and making it look worse (a smaller propane furnace with lower BTU output might run longer more efficient cycles than your current model).
It’s also hard for me to calculate exactly how much energy this heat pump will save you on AC with your rough numbers, but it seems like it would save you there too. My rough calculations show that your home actually leaks energy more slowly than my own, and yet you estimate you pay $80/month for AC (aka 800 kWh/month) while I only used 825 kWhs for cooling in 2020 and 749 in 2021. I’d expect your better insulated home to need less AC than mine so this points to the cooling efficiency of a new heat pump trouncing that of your existing AC, but the fact that I love hot temps and regularly leave my thermostat between 78 and 80 in the summer could be skewing the results a bit.
In the end it looks like a heat pump could save you $500-$1,000 per year in energy costs. If you subtract the cost of buying a new AC, propane furnace and propane tank from the cost of even a fancy heat pump like my own I still think you’ll come out ahead with the heat pump. If you lock in low kWh prices with solar or choose a much cheaper heat pump (like Mr Cool DIY’s 10.5 HSPF Universal Series unit for $4200 after options https://hvacdirect.com/mrcool-universal-48-000-btu-heat-pump-mdu18048.html) you’ll likely have slightly higher monthly bills but a bit lower total cost over the life of the unit because of the much cheaper purchase price.
If you do DIY I’d strongly recommend paying a few hundred bucks for a company to do a home energy audit and run a manual J calculation on your home to make sure you’re sizing it correctly, but based on my calculations here I think a heat pump is a slam dunk for you and their more detailed check should confirm that and help you pick the correct size (if you do this please post how the number of BTUs they estimate it’ll take to heat your home compares to what I calculated here). Hope this helps, and keep me posted on your journey.
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John Griffith
2021-01-19 at 5:33 pm
Absolutely love your site/blog, thank you. So glad I stumbled across it.
Love the way you think — put up a big fat array bc solar is so cheap, and don’t go crazy with changing appliances etc, electrify everything and get more panels if needed…
We live on a farm in the Upper Peninsula (UP) of Michigan. Cold and snowy. Avg high temp in 20’s and low 30’s Nov-March and only 60’s and 70’s May-Sept. Our big need is heating not cooling, but cooling is great for our rare southern flow with hot muggy days.
Low sun and lots of clouds in the winter. Long days and much “overproduction” in spring, summer, fall.
We are installing a 30kW array. As you note, panels and cheap. We have space so are doing a ground mount. Building own racking, single-axis tilt — will have up near 70 degrees in winter to see the sun and shed snow. Free and clear 180 view south from array (on bank of E-W creek). Also will have 10kW of VAWT to help in the winter when it windy and not sunny. Will run 2 EV’s off system, hopefully with V2G capability so we’ll have batteries.
We have a wood stove with free firewood (375 acres of maple and oak) to take the place of supplemental resistive heat when the heat pump will need help on the sub zero days.
I have a loader-backhoe, so there is not much extra cost for doing a ground-based heat pump, and we really need one to get 45-50 degree ground heat vs typical single digit or teen low overnight temps (and especially when it goes negative for several days).
So here is my question, finally: knowing we like to oversize, knowing that it’s a very large but modernly insulated farm house (6,500 ft2 — it’s gonna be a B&B when we’re done), knowing we can cheaply install a ground-based heat pump (and love having it the basement not outdoors all winter!), what make/ model/ size gb heat pump would you point me too? And would there be something like a mini-split in each room/ space that would work with the gbhp?
Wow, your setup sounds like it’s going to be awesome. One caution on the V2G car dream, most current EVs don’t support that, and even if they did you wouldn’t want to do it very often given the number of recharge cycles current lithium batteries support (I do expect we’ll see a bunch more V2G in the next 5-10 years are battery cycle life extends). I also don’t normally recommend ground based heat pumps because of the cost, but I think based on how cold the UP is and the fact that you can dig your own piping area you’re right to choose one. Another word of caution is to make sure you dig a large enough area for the pipes for the HP. You don’t want to dig too small and then find that you don’t have enough heat to efficiently heat your home in winter. As for a specific heat pump, I don’t have a ton of experience with ground based models, but I’ve heard good things about Nordic heating’s liquid to liquid heat pumps https://www.nordicghp.com/product/nordic-products/liquid-source-heat-pumps/liquid-to-water/w-series-residential/. That heat pump is designed to be used with radiant in floor heating though, and if you don’t have that already you might not want to rip up your house to add it (also, it won’t cool your house, but as you note that’s barely needed where you are).
You don’t mention how the house is heated now, but my initial recommendation is to try and find a heat pump that can tie into that, whether it be forced air, hydronic radiant, or whatever. If that is too hard then mini-splits are always an option, but they’ll be pricey for such a large house, because each split adds cost (they’re pretty easy to install though, so they’re not all bad). In terms of size, that can vary a lot depending on the surface area to volume ratio of your house along with its air sealing and insulation. Considering how much you’ll be spending on this I think it makes a lot of sense to get a professional to come in and do a blower door test and a Manual J calculation for the home. This should only cost a couple hundred bucks and if it lets you size your heat pump appropriately it’ll be more than worth it. In a best case scenario you’d find a company that also sells ground source heat pumps to do the test so they could at least pitch you on the models they carry (though I recommend doing your own research on HPs as well because sometimes installers won’t tell you about a much better model that they don’t carry). Hope this helps. Let me know if you have any other questions, and please do come back and provide an update whenever your project is completed, I’m excited to hear how it turns out! I’ve got some relatives in the UP, who knows maybe some day I’ll get to come up and visit your eco-B&B.
I will keep you posted on our project. Our current heat is primarily wood (Vermont Castings Defiant Encore catalytic stove, smokeless top-loading!) with supplemental propane heat (direct vent in 2 bathrooms and faux wood Vermont Castings propane vented stove in family room).
I will take your suggestion about the tests and professional analysis.
We are doing a major re-model and addition, so we could decide on radiant flooring. With AGW, in recent years we’ve had long spells of hot muggy “Wisconsin weather” so were hoping to build in AC too, especially thinking of B&B guests.
It would be awesome if you came for a visit! Planning to be done by the end of 2022.
Thanks again for your reply and all the info you provide.
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Ken Tarquinio
2020-11-28 at 5:29 pm
I live in San Jose, California where our climate is probably much milder than where you live. The average summer high is in the mid 80 degree range. However, in July and August it can easily reach the low 90 degrees. Very rarely does it ever go over 100 degrees. San Jose is also not very humid. So a slightly warmer temperature is not that uncomfortable. In the winter a “bitterly cold day” is around thirty degrees. Most seasons it never goes below freezing. However, usually nighttime temperatures in the winter are in the 40 or 50 degree range.
Our 1964 house still has the original gas “80 percent efficient” 100,000 BTU gas furnace. However, I understand that it is probably less efficient than that due to an inevitable loss of efficiency as it ages. I have no air conditioning. However, our house can get uncomfortable for two or three months in the middle of summer. I did a manual J analysis and it showed that my 100,000 BTU furnace was much too large and my ducts are to small for a modern day furnace of that size. In addition, about a third of the house is served by only one duct. That means that the upstairs heats up in a few minutes and the downstairs is perpetually cold during the heating season.
Electricity is very expensive hear. I have an electric car tariff so my rate is relatively low most of the day (at least for California). As you can see, the tariffs during peak times 4:00 PM to 9:00 PM are outrageously high! Part peak is from 3:00 to 4:00 PM and from 9:00PM to 12:00 AM with rates only moderately better.
Total Energy Rates ($ per kWh) PEAK PART-PEAK OFF-PEAK
Delivery Minimum Bill Amount ($ per meter per day) $0.32854
California Climate Credit (per household, per semiannual payment occurring in the April and October bill
cycles)
Surprisingly, we have lived in the house nearly 25 years and we have never had any problems with our furnace.
I have been considering replacing my furnace with a new smaller furnace. In part because a newer furnace would would use less energy and partly because a smaller furnace would run for longer periods so that the warm air would be more evenly distributed throughout the house. However, I doubt a new furnace will ever pay for itself.
I have also considered changing my furnace to a heat pump. However, my concern is that because of my high electricity tariffs, I will have much higher utility bills if I switch from a gas furnace to an heat pump. My reasoning is that much of the heating and cooling would occur during times when peak rates are in effect.
I have also considered adding a mini split downstairs instead because the ducts downstairs are limited to one register which is completely inadequate. I could then wait to replace the gas furnace until it breaks down.
Thanks for the great comment. 100,000 BTUs for San Jose is crazy, it’ll keep you warm but it’s definitely costing you money. That’s what builders used to do though, don’t put any insulation or air sealing in at all and just throw in a massive oversized furnace. You don’t mention the square footage of your house, but you’d need to be living in like an 8,000 sqft mansion to require that much heating there.
I think your idea of adding minisplits is a good one. You can save a lot if you feel capable going somewhere like https://mrcooldiy.com/ and DIYing it. If you’re going to have pros do it, you’ll probably spend more doing it in multiple installments instead of one fell swoop, since their time costs money.
As for CAs high electricity rates, I completely agree with you about them. But CA still has net metering, which means if you install a big enough solar array you won’t pay anything for power. CA also has high solar install prices because of this, but they’re low enough that it’s still profitable to install solar. If you really want to have a huge ROI again the answer is to DIY, but that’s even harder for solar since you need to get on the roof and if you don’t follow all the safety rules you can fall and get seriously injured.
I think the best answer is to find a company that does solar and heat pumps and pay for a home energy audit from them. That might cost a couple hundred bucks but it’ll give you a far better idea on the ROI of various options. Given that large differences between your peak and off peak power costs you may even want to consider a battery, but if you get a big solar array with net metering you won’t need to. Hope this helps!
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Alistair
2022-03-29 at 6:21 pm
I appreciated reading this article. I am currently looking at replacing oil heat and hot water ROI of a cold climate air source heat pump and standard electric heater. I factored in all savings I could, including reduced insurance, reduced maintenance and potential increase in home value to a buyer and came up with an ROI of about 11 years. (the upfront costs are very high, less a govt incentive). There are other non-tangible factors to consider too – reduced risk of catastrophic oil leak, savings from not having to replace the furnace in the future and of course, just the feel-good going green component. This is what I calculated in savings for my home in northern Ontario (we don’t currently use AC other than a small portable so this is just a guess)
Annually ——————————–
Fuel savings heat 534.42
Fuel savings hot water 435.51
savings burning less wood 250.00
savings maintenance 350.00
insurance savings 25.00
Additional cost of AC -300.00
total annual savings 1294.93
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John Katerenchuk
2021-10-06 at 12:33 am
I enjoyed your article and analysis. It was timely as I live in Southeastern PA (Lancaster County) and the AC and Propane Furnace is approaching 20 year of age. I had been thinking about replacement of both with a heat pump but my experiences while living in Georgia on some cold days were not very positive as the heat pump on very cold days would not keep the house warm and comfortable. I was worried if that might also be the result in PA. I was also wondering if the investment would be financially viable compared to our actual cooling cost and propane heating cost. Any help you might provide would be appreciated to get me headed in the right direction.
Profit Greenly (Post author)
2021-10-06 at 3:51 pm
Glad you liked it. Let me know what you pay for propane to fuel your existing furnace each year and I can get a better idea of how a heat pump would work financially for you (include both the total cost you pay to heat each year, how much propane that is, and the efficiency or AFUE rating of your existing furnace for a detailed answer). Even without that info I can say confidently that a heat pump will be able to heat your home just fine even on very cold days, because you live further South than me. I guess it’s possible that your home is bigger, leakier, and less well insulated than mine, but those are all problems that can be fixed, and if you read my net zero and profit post (https://profitgreenly.com/net-zero-and-profit/) you’ll see that my house is very far from being a Passive House and yet the heat pump still keeps us warm all by itself.
In terms of ROI a heat pump doesn’t cost much more than a stand-alone AC (particularly if you install it yourself). Mr. Money Mustache just wrote about doing a DIY heat pump install for just $4500 https://www.mrmoneymustache.com/2021/10/05/diy-heat-pump/. His unit isn’t quite as efficient as the one I got, but for $10,000 less I’m sure he’ll have a higher ROI.
Given that a heat pump can be over 400% efficient and a propane furnace can never surpass 100% efficiency, I think it’s likely that a heat pump will win out in the long term. Even if you burned propane in a generator at your house to power your heat pump you’d likely have a lower fuel cost across a whole winter than if you burned it purely for heat. Electricity prices are pretty low and stable here in PA so I don’t recommend doing this, it’s just an example. If you install solar on your roof you’re essentially locking in an electricity price till either those panels die (in 30+ years) or PA revokes our net metering law (I do expect this to happen eventually, but I bet they grandfather in existing installations). That means that the price to heat your home with a heat pump can be both very stable and very low. Propane on the other hand will likely fluctuation wildly in price in the near future (just look at Europe right now for an example of this) and so even if it happens to be cheaper now it likely won’t be over the long term (do send me your propane cost numbers from last year to check though, as I expect it’ll lose out to an efficient heat pump even now).
John Katerenchuk
2021-10-20 at 4:29 pm
Here are the basics of my HVAC setup. Outside traditional AC unit. Approaching 20 years of age. Inside Propane furnace. Nordyne G6RC 080c-16B fed from a 500 gal buried Propane tank outside. Also approaching 20 years of age. Also, a Propane water heater that was replaced about 3 years ago.
I know the AC unit will need a full replacement next time if breaks down. The furnace has only required minimal yearly small service charges and replacement parts costs most of which I buy and do myself. I could not find any information on the furnace efficiency but on the manufacturers sticker it shows a input of 80,000 BTUH and a output of 73,000 BTUH. If that represents the efficiency then it would seem to be 91.2%.
Reviewing my Propane cost and usage back to 2007 on average for the furnace and the hot water heater I use 575 Gal/year. Cost swings all over the place depending upon year and time of year to fill the tank. The lowest is $1.02/Gal in 2016 and the highest is 2.52/Gal in 2014. My last fill was last month and that was $1.66/Gal. The average over the whole period is $1.65/Gal. So at the average price, my Propane cost per year is $950. At the lowest, it is $580 and the highest is $1450. I cannot tell how much of the Propane is used for Hot Water heating but I would think it would be no more than 10%. Additionally, in the equation, I need to think about the cost of replacing the inground 500 Gal propane tank. I am not sure of the lifetime of these tanks (it is approaching 20 years). It would be a shame to ignore this cost in the comparison analysis of heat pump/electric heating vs heat pump and Propane heating only to find the Propane tank needed to be replaced a couple of years later at a high cost.
Looking at the Electrical side it appears my bill increases by about $80 per month during the months when the AC is needed. Which is usually about 3 months per season. So roughly the AC costs about $250 per year.
I hope that provides you with the information you requested. From a cost analysis it comes down to comparing Heat Pump with Electric backup versus Heat Pump with Propane backup. I quickly looked at GeoThermal Heat pumps but the high up front cost would take more years to payback than we expect to be around in this house.
Profit Greenly (Post author)
2021-10-26 at 3:16 pm
Thanks for the detailed info, and sorry for the slow reply. It looks like your furnace is more commonly sold as a Frigidaire FG6RC 080c-16B with a claimed AFUE of 92.1% so your division is about right. Sadly your having both a water heater and a furnace running on propane mean that I can’t be exact in my calculations, but using the standard assumption that the water heater uses 25% of your annual propane and the furnace uses the other 75%. That means You spend about $720/year fueling your furnace with 436 gallons of propane. A gallon of propane at 60 F contains 91,502 BTUs of energy so your 92% efficient furnace is turning these 460 gallons into 36,733,893 BTUs to heat your home over an average winter.
To get this same amount of heat from a heat pump you need to know its efficiency. Ground source heat pumps will give a single efficiency rating called a COP that they operate at pretty much all the time. A COP of 4 means 400% efficient. For air source heat pumps efficiency increases as the outdoor air temps increase, so they’re rated by HSPF which averages their efficiency across an estimated heating season. You can roughly convert HSPF to COP by multiplying it by 0.293, but the actual weather each winter will change your true efficiency year to year (climate change is likely to continue warming the world in the coming years so this efficiency will likely go up a bit over time). My heat pump has a 13 HSPF so it’s around 380% efficient. If I put 1 kWh into an electric resistance heater of 100% efficiency I get 3,412 BTUs out, so if I instead put it into my 380% efficient heat pump I get 12,966 BTUs out.
Dividing the 36,733,893 BTUs I calculated that it takes to heat your home by the 12,966 BTUs my heat pump creates from 1 kWh over an average winter I find that it’d take 2,833 kWh to heat your home with my heat pump. Well, there’s one more caveat. When it gets really cold my heat pump supplements its heating with electric resistance heat that’s only 100% efficient.
In 2020 I used 3,730 kWhs to power my heat pump for heating and another 546 kWhs to power my backup resistance heat on a few super cold days. A cheaper heat pump will use more backup heating, so let’s just add the full 546 kWhs I used last year to my estimate of 2,833 kWhs to heat you home. That’s still only 3,379 kWhs per year. With power costing around 10 cents per kWh in PA that would be only $338/year, far lower than the $720 you’re paying for propane! Installing solar dropped my $/kWh down to around $0.07 so with that your heating could cost only $236/year and that price would be locked in for the life of the heat pump (likely 15 years) unless PA scraps its existing net metering and SREC laws.
This isn’t a perfect prediction because there are still variables like what temperature your propane is actually delivered at (which changes how many BTU per gallon) and the exact temperature range your home experiences over a year. Your existing furnace also seems oversized for your home (a common problem in the US) and that could be reducing it’s efficiency and making it look worse (a smaller propane furnace with lower BTU output might run longer more efficient cycles than your current model).
It’s also hard for me to calculate exactly how much energy this heat pump will save you on AC with your rough numbers, but it seems like it would save you there too. My rough calculations show that your home actually leaks energy more slowly than my own, and yet you estimate you pay $80/month for AC (aka 800 kWh/month) while I only used 825 kWhs for cooling in 2020 and 749 in 2021. I’d expect your better insulated home to need less AC than mine so this points to the cooling efficiency of a new heat pump trouncing that of your existing AC, but the fact that I love hot temps and regularly leave my thermostat between 78 and 80 in the summer could be skewing the results a bit.
In the end it looks like a heat pump could save you $500-$1,000 per year in energy costs. If you subtract the cost of buying a new AC, propane furnace and propane tank from the cost of even a fancy heat pump like my own I still think you’ll come out ahead with the heat pump. If you lock in low kWh prices with solar or choose a much cheaper heat pump (like Mr Cool DIY’s 10.5 HSPF Universal Series unit for $4200 after options https://hvacdirect.com/mrcool-universal-48-000-btu-heat-pump-mdu18048.html) you’ll likely have slightly higher monthly bills but a bit lower total cost over the life of the unit because of the much cheaper purchase price.
If you do DIY I’d strongly recommend paying a few hundred bucks for a company to do a home energy audit and run a manual J calculation on your home to make sure you’re sizing it correctly, but based on my calculations here I think a heat pump is a slam dunk for you and their more detailed check should confirm that and help you pick the correct size (if you do this please post how the number of BTUs they estimate it’ll take to heat your home compares to what I calculated here). Hope this helps, and keep me posted on your journey.
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John Griffith
2021-01-19 at 5:33 pm
Absolutely love your site/blog, thank you. So glad I stumbled across it.
Love the way you think — put up a big fat array bc solar is so cheap, and don’t go crazy with changing appliances etc, electrify everything and get more panels if needed…
We live on a farm in the Upper Peninsula (UP) of Michigan. Cold and snowy. Avg high temp in 20’s and low 30’s Nov-March and only 60’s and 70’s May-Sept. Our big need is heating not cooling, but cooling is great for our rare southern flow with hot muggy days.
Low sun and lots of clouds in the winter. Long days and much “overproduction” in spring, summer, fall.
We are installing a 30kW array. As you note, panels and cheap. We have space so are doing a ground mount. Building own racking, single-axis tilt — will have up near 70 degrees in winter to see the sun and shed snow. Free and clear 180 view south from array (on bank of E-W creek). Also will have 10kW of VAWT to help in the winter when it windy and not sunny. Will run 2 EV’s off system, hopefully with V2G capability so we’ll have batteries.
We have a wood stove with free firewood (375 acres of maple and oak) to take the place of supplemental resistive heat when the heat pump will need help on the sub zero days.
I have a loader-backhoe, so there is not much extra cost for doing a ground-based heat pump, and we really need one to get 45-50 degree ground heat vs typical single digit or teen low overnight temps (and especially when it goes negative for several days).
So here is my question, finally: knowing we like to oversize, knowing that it’s a very large but modernly insulated farm house (6,500 ft2 — it’s gonna be a B&B when we’re done), knowing we can cheaply install a ground-based heat pump (and love having it the basement not outdoors all winter!), what make/ model/ size gb heat pump would you point me too? And would there be something like a mini-split in each room/ space that would work with the gbhp?
Thanks!
Wow, your setup sounds like it’s going to be awesome. One caution on the V2G car dream, most current EVs don’t support that, and even if they did you wouldn’t want to do it very often given the number of recharge cycles current lithium batteries support (I do expect we’ll see a bunch more V2G in the next 5-10 years are battery cycle life extends). I also don’t normally recommend ground based heat pumps because of the cost, but I think based on how cold the UP is and the fact that you can dig your own piping area you’re right to choose one. Another word of caution is to make sure you dig a large enough area for the pipes for the HP. You don’t want to dig too small and then find that you don’t have enough heat to efficiently heat your home in winter. As for a specific heat pump, I don’t have a ton of experience with ground based models, but I’ve heard good things about Nordic heating’s liquid to liquid heat pumps https://www.nordicghp.com/product/nordic-products/liquid-source-heat-pumps/liquid-to-water/w-series-residential/. That heat pump is designed to be used with radiant in floor heating though, and if you don’t have that already you might not want to rip up your house to add it (also, it won’t cool your house, but as you note that’s barely needed where you are).
You don’t mention how the house is heated now, but my initial recommendation is to try and find a heat pump that can tie into that, whether it be forced air, hydronic radiant, or whatever. If that is too hard then mini-splits are always an option, but they’ll be pricey for such a large house, because each split adds cost (they’re pretty easy to install though, so they’re not all bad). In terms of size, that can vary a lot depending on the surface area to volume ratio of your house along with its air sealing and insulation. Considering how much you’ll be spending on this I think it makes a lot of sense to get a professional to come in and do a blower door test and a Manual J calculation for the home. This should only cost a couple hundred bucks and if it lets you size your heat pump appropriately it’ll be more than worth it. In a best case scenario you’d find a company that also sells ground source heat pumps to do the test so they could at least pitch you on the models they carry (though I recommend doing your own research on HPs as well because sometimes installers won’t tell you about a much better model that they don’t carry). Hope this helps. Let me know if you have any other questions, and please do come back and provide an update whenever your project is completed, I’m excited to hear how it turns out! I’ve got some relatives in the UP, who knows maybe some day I’ll get to come up and visit your eco-B&B.
John Griffith
2021-01-19 at 8:59 pm
Thanks for your complete reply!
I will keep you posted on our project. Our current heat is primarily wood (Vermont Castings Defiant Encore catalytic stove, smokeless top-loading!) with supplemental propane heat (direct vent in 2 bathrooms and faux wood Vermont Castings propane vented stove in family room).
I will take your suggestion about the tests and professional analysis.
We are doing a major re-model and addition, so we could decide on radiant flooring. With AGW, in recent years we’ve had long spells of hot muggy “Wisconsin weather” so were hoping to build in AC too, especially thinking of B&B guests.
It would be awesome if you came for a visit! Planning to be done by the end of 2022.
Thanks again for your reply and all the info you provide.
Much appreciated!
Incredibly janky port of comments from my old wordpress site.
Ken Tarquinio
2020-11-28 at 5:29 pm
I live in San Jose, California where our climate is probably much milder than where you live. The average summer high is in the mid 80 degree range. However, in July and August it can easily reach the low 90 degrees. Very rarely does it ever go over 100 degrees. San Jose is also not very humid. So a slightly warmer temperature is not that uncomfortable. In the winter a “bitterly cold day” is around thirty degrees. Most seasons it never goes below freezing. However, usually nighttime temperatures in the winter are in the 40 or 50 degree range.
Our 1964 house still has the original gas “80 percent efficient” 100,000 BTU gas furnace. However, I understand that it is probably less efficient than that due to an inevitable loss of efficiency as it ages. I have no air conditioning. However, our house can get uncomfortable for two or three months in the middle of summer. I did a manual J analysis and it showed that my 100,000 BTU furnace was much too large and my ducts are to small for a modern day furnace of that size. In addition, about a third of the house is served by only one duct. That means that the upstairs heats up in a few minutes and the downstairs is perpetually cold during the heating season.
Electricity is very expensive hear. I have an electric car tariff so my rate is relatively low most of the day (at least for California). As you can see, the tariffs during peak times 4:00 PM to 9:00 PM are outrageously high! Part peak is from 3:00 to 4:00 PM and from 9:00PM to 12:00 AM with rates only moderately better.
Total Energy Rates ($ per kWh) PEAK PART-PEAK OFF-PEAK
Summer Usage $0.47925 (I) $0.36876 (I) $0.16675 (I)
Winter Usage $0.35214 (I) $0.33544 (I) $0.16675 (I)
Delivery Minimum Bill Amount ($ per meter per day) $0.32854
California Climate Credit (per household, per semiannual payment occurring in the April and October bill
cycles)
Surprisingly, we have lived in the house nearly 25 years and we have never had any problems with our furnace.
I have been considering replacing my furnace with a new smaller furnace. In part because a newer furnace would would use less energy and partly because a smaller furnace would run for longer periods so that the warm air would be more evenly distributed throughout the house. However, I doubt a new furnace will ever pay for itself.
I have also considered changing my furnace to a heat pump. However, my concern is that because of my high electricity tariffs, I will have much higher utility bills if I switch from a gas furnace to an heat pump. My reasoning is that much of the heating and cooling would occur during times when peak rates are in effect.
I have also considered adding a mini split downstairs instead because the ducts downstairs are limited to one register which is completely inadequate. I could then wait to replace the gas furnace until it breaks down.
I have also considered adding solar.
Profit Greenly (Post author)
2020-12-09 at 3:09 am
Thanks for the great comment. 100,000 BTUs for San Jose is crazy, it’ll keep you warm but it’s definitely costing you money. That’s what builders used to do though, don’t put any insulation or air sealing in at all and just throw in a massive oversized furnace. You don’t mention the square footage of your house, but you’d need to be living in like an 8,000 sqft mansion to require that much heating there.
I think your idea of adding minisplits is a good one. You can save a lot if you feel capable going somewhere like https://mrcooldiy.com/ and DIYing it. If you’re going to have pros do it, you’ll probably spend more doing it in multiple installments instead of one fell swoop, since their time costs money.
As for CAs high electricity rates, I completely agree with you about them. But CA still has net metering, which means if you install a big enough solar array you won’t pay anything for power. CA also has high solar install prices because of this, but they’re low enough that it’s still profitable to install solar. If you really want to have a huge ROI again the answer is to DIY, but that’s even harder for solar since you need to get on the roof and if you don’t follow all the safety rules you can fall and get seriously injured.
I think the best answer is to find a company that does solar and heat pumps and pay for a home energy audit from them. That might cost a couple hundred bucks but it’ll give you a far better idea on the ROI of various options. Given that large differences between your peak and off peak power costs you may even want to consider a battery, but if you get a big solar array with net metering you won’t need to. Hope this helps!