You live in Virginia beach. The title of this thread is Heat Pump in Northern Climates.
Heat Pump in Northern Climates?
- Thread starter tbm5690
- Start date
I know where I live.
In the past I’ve lived in Winnipeg, northern Vermont, and Colorado.
No heat pumps in any of those.
Heated with oil, and propane.
Natural gas is my current choice. In my mild climate it’s cheapest.
It would’ve been cheapest in Vermont, if it had been an option.
Ended up with oil. Heat pump was cheaper to install in Vermont but far more expensive to operate.
In the past I’ve lived in Winnipeg, northern Vermont, and Colorado.
No heat pumps in any of those.
Heated with oil, and propane.
Natural gas is my current choice. In my mild climate it’s cheapest.
It would’ve been cheapest in Vermont, if it had been an option.
Ended up with oil. Heat pump was cheaper to install in Vermont but far more expensive to operate.
Price of oil. Price of electricity. Price of NG. Price of propane. Efficiency of each system.
They are all factors. They vary.
But please don’t conflate NG and propane.
Very different commodities.
They are all factors. They vary.
But please don’t conflate NG and propane.
Very different commodities.
I'd say I'm near the "northern climes" area here in NJ. We at least see some consistent winter temperatures. I replaced my old oil furnace with a heat pump about 3 years ago. It is far cheaper than oil was for us and it works pretty well. I believe ours operates down to 25°F, but I may be off by a few degrees. After that it uses a coil backup to provide heat to the house. Other than the fact it is still a bit noisy, but still quieter than the oil furnace was, I have no other complaints. It is better in every way than the oil was.
CCASHP - Cold Climate Air Source Heat Pump. Times are changing.
Your words “ had it been an option” describes the propane vs natural gas issue. In my area heat pumps compete with propane down to about 27 to 30 F. Not so much with natural gas.
Here are the current $ per Giga Joule (GJ) of energy taking into account efficiencies of my equipment, current local prices and converted to US dollars. Keep mind the decision to purchase a heat pump is easy if you decide upon central air conditioning.
Electrical resistance heating $31.34
Heating with a heat pump at COP of 2 ( near freezing conditions) $14.86
Heating with a heat pump at COP of 3 ( higher than freezing conditions ) $10.44
Propane $42
Natural gas $15.00
Fir Firewood $13.00
These are for my area with my efficiency numbers and prices. Everyone can do their own. I don’t have natural gas in my mountainous home even though I live next to Alberta. I can’t control the temps but use a heat pump down to 27 F and then my system automatically switches to a high efficiency propane boiler. Once on propane I will also start up the airtight wood stove in the morning.
I encourage every one to use GJ because we are dealing with prices per kwhr, therms, BTU’s or whatever your local area uses. It represents the amount paid per equivalent amount of energy used. For costs make sure you add in all the added “service costs” and taxes.
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Astro, are you really paying $28.30 per thousand cubic feet of natural gas? JC.
dnewton3
Staff member
I worked in HVAC cooling engineering for several years.
I can say with certainty that a HP does not make sense in your situation.
A HP in that area will spend most of it's time in defrost mode and have the heater elements running quite often; not efficient. HPs are fantastic when the outdoor ambients are at/above freezing. As the temps drop below freezing, they don't do nearly as well.
Because you already have a good new furnace, I question why you need a HP? If it is a "back-up" heat capability you are worried about (having heat if the furnace fails), then I suggest choosing a couple of blue-flame wall heaters. They work great, and don't even need electricity. As long as you have gas, you have heat. That's exactly how I have my system set up in my basement. And two blue-flame wall heat units are FAR cheaper than a HP, and probably more reliable in an emergency.
I can say with certainty that a HP does not make sense in your situation.
A HP in that area will spend most of it's time in defrost mode and have the heater elements running quite often; not efficient. HPs are fantastic when the outdoor ambients are at/above freezing. As the temps drop below freezing, they don't do nearly as well.
Because you already have a good new furnace, I question why you need a HP? If it is a "back-up" heat capability you are worried about (having heat if the furnace fails), then I suggest choosing a couple of blue-flame wall heaters. They work great, and don't even need electricity. As long as you have gas, you have heat. That's exactly how I have my system set up in my basement. And two blue-flame wall heat units are FAR cheaper than a HP, and probably more reliable in an emergency.
Post your $ per GJ in your assumptions. You might be surprised. I use a heat pump because I can run it for $14.86 per GJ provided. Propane costs $42 per GJ. As for the defrost cycle, I mentioned it before and it doesn’t take long and is not often at my lower limit of 27 F. Indiana natural gas is $24.98 per 1000 ft3 plus what ever else is on your bill. Also, I have been saying that the heat pump decision is always predicated that you want AC in the summer and would have bought a central AC anyway. The incremental cost to go to the heat pump is minor.
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dnewton3
Staff member
I am being specific to the OPs situation. Read my second line which you quoted. "in your situation" was referring to the following ...
1) he's already paid for a new NG condencing furnace, presumably capable of carrying his whole heat load demand
2) to get a HP system capable of that same heating load in his area, he'd most probably have to get an entire new cooling system as well. He can't just replace the exterior compressor unit and expect to carry the same heating load demand. I presume his current indoor coil is sized for his cooling load (probably not huge in ND). But a HP unit needs a larger indoor coil (relative to cooling loads) to carry the heat demand he'll have in winter. So, in essence, he's going to have to buy an entire new cooling system (exterior compressor unit and indoor coil), and also have the added rework to his ducting (to fit a larger coil), and for what purpose??? As a "just in case" he needs heat when his furnace fails?
Again, if he's only looking for back-up (in case of emergency) heating, two or three blue-flame heaters are FAR, FAR cheaper and FAR more reliable. For Pete's sake, why pay for an entire HP system when he already just paid for a entire furnace system??? Having one or the other makes sense; having BOTH systems is a complete waste of money. If the desired effect is simply to provide an emergency back-up, a few low cost HG wall heaters are by far more sensible.
However, if he's looking to save money using HP versus the brand new 96% eff furnace he just paid for, well, there's pretty much no way he'll save enough money. Becuase he not only has to include all the costs we talk about (cost of the "fuel" be it NG or electricity) but he ALSO has to include the cost of an entirely new furnace THAT WILL PRESUMABLY SIT IDLE WHILE THE HP RUNS. Take THAT cost and include it in your calculations folks!
The OP initially said he "just replaced" his furnace system. Yet now "it's time to replace the outside AC coil". If he knew that he'd be replacing an AC unit (nearly) immediately after doing the heating system, he should have done an ENTIRE SYSTEM all at the same time. He's trying to engineer savings into his choice after already buying 1/2 the whole HVAC system. It's too late; he chose a path. What he'd have to spend to get a PROPERLY SIZED HP system will eat up what savings he'll get. A properly sized HP system is either engineered to work on it's own for all seasons, or as a dual-fuel system ONLY if it's sized and put together as a properly selected package from the get-go. Trying to engineer savings into a HP after-thought system after one already committed to a traditional NG furnace is, well, silly.
But then again, this is BITOG; whether it's syn oils changed every 4k miles, or buying a HVAC system redundant to one you just bought, wasting money is a priorty for some here ...
1) he's already paid for a new NG condencing furnace, presumably capable of carrying his whole heat load demand
2) to get a HP system capable of that same heating load in his area, he'd most probably have to get an entire new cooling system as well. He can't just replace the exterior compressor unit and expect to carry the same heating load demand. I presume his current indoor coil is sized for his cooling load (probably not huge in ND). But a HP unit needs a larger indoor coil (relative to cooling loads) to carry the heat demand he'll have in winter. So, in essence, he's going to have to buy an entire new cooling system (exterior compressor unit and indoor coil), and also have the added rework to his ducting (to fit a larger coil), and for what purpose??? As a "just in case" he needs heat when his furnace fails?
Again, if he's only looking for back-up (in case of emergency) heating, two or three blue-flame heaters are FAR, FAR cheaper and FAR more reliable. For Pete's sake, why pay for an entire HP system when he already just paid for a entire furnace system??? Having one or the other makes sense; having BOTH systems is a complete waste of money. If the desired effect is simply to provide an emergency back-up, a few low cost HG wall heaters are by far more sensible.
However, if he's looking to save money using HP versus the brand new 96% eff furnace he just paid for, well, there's pretty much no way he'll save enough money. Becuase he not only has to include all the costs we talk about (cost of the "fuel" be it NG or electricity) but he ALSO has to include the cost of an entirely new furnace THAT WILL PRESUMABLY SIT IDLE WHILE THE HP RUNS. Take THAT cost and include it in your calculations folks!
The OP initially said he "just replaced" his furnace system. Yet now "it's time to replace the outside AC coil". If he knew that he'd be replacing an AC unit (nearly) immediately after doing the heating system, he should have done an ENTIRE SYSTEM all at the same time. He's trying to engineer savings into his choice after already buying 1/2 the whole HVAC system. It's too late; he chose a path. What he'd have to spend to get a PROPERLY SIZED HP system will eat up what savings he'll get. A properly sized HP system is either engineered to work on it's own for all seasons, or as a dual-fuel system ONLY if it's sized and put together as a properly selected package from the get-go. Trying to engineer savings into a HP after-thought system after one already committed to a traditional NG furnace is, well, silly.
But then again, this is BITOG; whether it's syn oils changed every 4k miles, or buying a HVAC system redundant to one you just bought, wasting money is a priorty for some here ...
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Ha ha, I thought you talking to me, since I did the posting immediate prior to yours. Yes I agree. My stuff was more to introduce people to the concept of heat pumps in cold weather ( no lower than 27 F) and also point out the price of natural gas has risen a lot. If a person is buying a new central AC system, they should look at a heat pump. IMHOI am being specific to the OPs situation. Read my second line which you quoted. "in your situation" was referring to the following ...
1) he's already paid for a new NG condencing furnace, presumably capable of carrying his whole heat load demand
2) to get a HP system capable of that same heating load in his area, he'd most probably have to get an entire new cooling system as well. He can't just replace the exterior compressor unit and expect to carry the same heating load demand. I presume his current indoor coil is sized for his cooling load (probably not huge in ND). But a HP unit needs a larger indoor coil (relative to cooling loads) to carry the heat demand he'll have in winter. So, in essence, he's going to have to buy an entire new cooling system (exterior compressor unit and indoor coil), and also have the added rework to his ducting (to fit a larger coil), and for what purpose??? As a "just in case" he needs heat when his furnace fails?
Again, if he's only looking for back-up (in case of emergency) heating, two or three blue-flame heaters are FAR, FAR cheaper and FAR more reliable. For Pete's sake, why pay for an entire HP system when he already just paid for a entire furnace system??? Having one or the other makes sense; having BOTH systems is a complete waste of money. If the desired effect is simply to provide an emergency back-up, a few low cost HG wall heaters are by far more sensible.
However, if he's looking to save money using HP versus the brand new 96% eff furnace he just paid for, well, there's pretty much no way he'll save enough money. Becuase he not only has to include all the costs we talk about (cost of the "fuel" be it NG or electricity) but he ALSO has to include the cost of an entirely new furnace THAT WILL PRESUMABLY SIT IDLE WHILE THE HP RUNS. Take THAT cost and include it in your calculations folks!
The OP initially said he "just replaced" his furnace system. Yet now "it's time to replace the outside AC coil". If he knew that he'd be replacing an AC unit (nearly) immediately after doing the heating system, he should have done an ENTIRE SYSTEM all at the same time. He's trying to engineer savings into his choice after already buying 1/2 the whole HVAC system. It's too late; he chose a path. What he'd have to spend to get a PROPERLY SIZED HP system will eat up what savings he'll get. A properly sized HP system is either engineered to work on it's own for all seasons, or as a dual-fuel system ONLY if it's sized and put together as a properly selected package from the get-go. Trying to engineer savings into a HP after-thought system after one already committed to a traditional NG furnace is, well, silly.
But then again, this is BITOG; whether it's syn oils changed every 4k miles, or buying a HVAC system redundant to one you just bought, wasting money is a priorty for some here ...
We use Mitsubishi-MXZ-4C36NAHZ2-U1 in one location. It's predecessor (new model is more efficient) had a COP of between 2.83 to 2.12 (min to max output) at -13
Multi-zone systems have a lower efficiency than single-zone systems so we blend them but my preference is to have multiple single-zone systems (allows for independent by-the-room-use) and we've run 48,000 BTU of inverters on a 40 C hot day (setpoint at 21 C) using just under 3,000 watts of power for the entire house (refrigerators, pool pump running) on the Honda EU7000isnan
The Mitsubishis of 5 years ago were totally different than the new models available in 2021
Multi-zone systems have a lower efficiency than single-zone systems so we blend them but my preference is to have multiple single-zone systems (allows for independent by-the-room-use) and we've run 48,000 BTU of inverters on a 40 C hot day (setpoint at 21 C) using just under 3,000 watts of power for the entire house (refrigerators, pool pump running) on the Honda EU7000isnan
The Mitsubishis of 5 years ago were totally different than the new models available in 2021
The Bosch IDS 2.0 heat pump runs 10 mins to reach the set temp while in the mid 20's outside and it comes on twice per hour. The air temp coming out of the registers is 90F at an outside temp of 23F. It rarely needs to even run in stage 2 and most of the time stays in stage 1. Electricity here is $0.14 per kWh and oil is $3.09 per gallon. At these costs the heat pump is significantly less to run even down to 20F compared to the cost of oil. The HSPF is 10.5 and my system, because it's a dual-fuel, does not have a heating element.
OP here chiming in....originally posted this Spring and my question was basically if I'm already paying for a new A/C coil outside does it make sense to spend a bit more and make it a heat pump considering my climate and cheap cost of NG. I did have the indoor coil replaced in tandem with the new furnace preemptively since it made sense so the plan was always to do a whole new system. I ended up just going straight A/C and no HP, unrelated but wasn't aware the indoor coil has to size up for a heat pump so that's good to know now for any future endeavors. I thought maybe given the slim price difference maybe it would make sense to just do HP even with little seasonal heating use but it became clear that was not the case.
dnewton3
Staff member
Here's a quick laymans summary of the difference between AC and HP, and why they're not directly interchangeable ...
Quick explanation of the systems:
AC and Furnace combo: uses one system to cool and a different one to heat. The only common element is the blower in the furnace, as it has to move the air in the house for both cooling and heating. But the heat exchangers are separate units and completely isolated to their seasonal task. Typically in an upflow system the furnace sits below the indoor evap coil.
HP system: uses the outdoor compressor and coil in conjunction with the indoor coil for both heating and cooling; there is no separate heat exchanger for each season. The indoor unit has only one heat exchanger for both heating and cooling, and the blower again does all seasons.
First, you have to understand about heat loss and heat gain as it relates to the house. It is VERY important to think of it as a heating (or cooling) rate, and not only a capacity. It's not just "30,000 BTUs", but it needs to be understood as a load/time (ex: 30,000 BTUs/hr). The BTU loss per hour of your dwelling is based on construction items such as insualtion, shading of trees, number and quality of windows and doors, etc. A good HVAC tech will always do his own load-loss calculations based on many standardized tools in the HVAC industry. (pretty much anyone can estimate it with today's internet tools, but a good HVAC tech will do a better job than Joe Average).
Assumptions for the example:
temperate zone: average expected high of 85F in summer and low of 10F in winter
preferred indoor temp: 70F year round
Thefore the HVAC system must be capable of providing BTU/hr make up in summer with enough energy to satisfy the 15F max expected delta, and 60F max delta in winter. You don't choose a system based on capacity, you "size" a system to accomplish holding your desired setpoint against the expected max normal temps. The capacity isn't an input, it's a result of saying:
* If I want to hold a 15F delta in summer, I need XX,xxx BTUs per hour. (house loses 22k BTUs/hr; a 24k BTU cooling system will suffice with a small buffer of excess capacity)
* If I want to hold a 60F delta in winter, I need YY,yyy BTUs per hour. (house loses 68k BTUs/hr; a 75k BTU heat system will suffice with a buffer of excess capacity)
Your house has a smaller delta to overcome in summer versus winter; pretty typical for all of North America. The ratio (cooling to heating) may be different (FL versus ND), but the concept is the same. Heating loads are often larger than cooling loads for comfortable indoor living.
In the assumed example, using a traditional AC and Furnace system, the summer max expected load will be an average temp delta of 15F (85-70). If it's cooler than 85F outside, the AC will run intermittently as it can satisfy the load. If it's warmer outside than 85F, the house might rise inside above the 70F setpoint because the system cannot keep up with the cooling loss; in theory if it's 90F outside and you have capacity/hr for a 15 degF delta, then you'll get 75F inside despite your desire to have 70F. So in the warmer months, the system should be sized to overcome a thermal loss of X BTUs/hr up to the 15 deg F delta. The outdoor coil might be a 2.5-ton unit and the indoor coil will be similar. This is always adjusted a bit depending on humidity averages, etc. But overall, the AC indoor coil will be sized for that cooling load loss and a 15 degF delta. The furnace, on the other hand, will have to make up a 60 degF delta (70-10) at that same BTU/hr loss. So the furnace has to supply many more BTUs to overcome the loss rate. Whereas the indoor coil may have to provide up to 22k BTUs/hr, the furnace may have to provide 68k BTUs/hr. These are generalizations for the example, but you get the idea. Also, the condensing and evap processes move from side to side in HP whereas they are set in AC. With a HP system, you evaporate inside in summer, but you condense inside in winter. There are all kinds of nuances that are different between the two concepts and the application of different coils and their operational parameters.
Now, if you take away the furnace system and now decide you want a HP system, that indoor AC coil which only had to supply 22k BTUs/hr in summer, now has to supply 68k BTUs/hr in winter. Suddenly that smaller indoor cooling coil is not large enough to be an indoor heating coil. So in HP systems, the HP indoor coil is typically larger because it has to make up a larger delta-T loss.
Soooooooo ....
My point in the OPs quest is that he had already purchased a heating system based on a traditional Furnace/AC concept, and therefore the indoor coil is undersized for the heating need (especially in ND !!!). Add to that, we understand the fact that he now has made us aware that he had bought a new indoor coil along with the furnace. So if he wants to change to a HP concept after the fact, he not only is wasting the use of the furnace, but he also is going to have to toss out a brand new undersized indoor coil in favor of an indoor coil that is large enough to do heating in addition to cooling.
Now do your cost analysis. Yes, often electricity can be cheaper in a "per hour" use factor. But if you now throw in a furnce that won't be used much at all (wasted money spent) and a brand new indoor coil tossed in the trash (lots more wasted money spent), and the purchase of a larger indoor coil (more money spent), and the need to modify the ductwork for the new larger indoor coil ... welll ..... you get the picture now?????
If you want a dual-fuel or HP system, you have to commit to that concept up front. You cannot do it after the fact; you'll NEVER recoup the costs associated with modifying the systems in retrospect with the supposed "savings" of using a HP. When you toss thousands of dollars in the garbage because you bought a system that won't provide what you need, the ROI of the HP savings is urinated away very, very quickly.
- HP systems make excellent sense in warm and moderate temps (above 40F) as they are very efficient
- HP systems can work decently in cold temps (above 25F) as they are moderately efficient
- HP systems struggle in ever colder temps (below 25F). (Its not that they don't work; it's that they defrost often and use heat packs which are not nearly as efficient as the HP process; the colder it gets the more they defrost and the more they rely on the "kicker heat" aka toaster coils).
- HP systems will NEVER make sense when you try to bastardize a new Furnace/AC system into something it wasn't designed to be.
That's my take on it.
Quick explanation of the systems:
AC and Furnace combo: uses one system to cool and a different one to heat. The only common element is the blower in the furnace, as it has to move the air in the house for both cooling and heating. But the heat exchangers are separate units and completely isolated to their seasonal task. Typically in an upflow system the furnace sits below the indoor evap coil.
HP system: uses the outdoor compressor and coil in conjunction with the indoor coil for both heating and cooling; there is no separate heat exchanger for each season. The indoor unit has only one heat exchanger for both heating and cooling, and the blower again does all seasons.
First, you have to understand about heat loss and heat gain as it relates to the house. It is VERY important to think of it as a heating (or cooling) rate, and not only a capacity. It's not just "30,000 BTUs", but it needs to be understood as a load/time (ex: 30,000 BTUs/hr). The BTU loss per hour of your dwelling is based on construction items such as insualtion, shading of trees, number and quality of windows and doors, etc. A good HVAC tech will always do his own load-loss calculations based on many standardized tools in the HVAC industry. (pretty much anyone can estimate it with today's internet tools, but a good HVAC tech will do a better job than Joe Average).
Assumptions for the example:
temperate zone: average expected high of 85F in summer and low of 10F in winter
preferred indoor temp: 70F year round
Thefore the HVAC system must be capable of providing BTU/hr make up in summer with enough energy to satisfy the 15F max expected delta, and 60F max delta in winter. You don't choose a system based on capacity, you "size" a system to accomplish holding your desired setpoint against the expected max normal temps. The capacity isn't an input, it's a result of saying:
* If I want to hold a 15F delta in summer, I need XX,xxx BTUs per hour. (house loses 22k BTUs/hr; a 24k BTU cooling system will suffice with a small buffer of excess capacity)
* If I want to hold a 60F delta in winter, I need YY,yyy BTUs per hour. (house loses 68k BTUs/hr; a 75k BTU heat system will suffice with a buffer of excess capacity)
Your house has a smaller delta to overcome in summer versus winter; pretty typical for all of North America. The ratio (cooling to heating) may be different (FL versus ND), but the concept is the same. Heating loads are often larger than cooling loads for comfortable indoor living.
In the assumed example, using a traditional AC and Furnace system, the summer max expected load will be an average temp delta of 15F (85-70). If it's cooler than 85F outside, the AC will run intermittently as it can satisfy the load. If it's warmer outside than 85F, the house might rise inside above the 70F setpoint because the system cannot keep up with the cooling loss; in theory if it's 90F outside and you have capacity/hr for a 15 degF delta, then you'll get 75F inside despite your desire to have 70F. So in the warmer months, the system should be sized to overcome a thermal loss of X BTUs/hr up to the 15 deg F delta. The outdoor coil might be a 2.5-ton unit and the indoor coil will be similar. This is always adjusted a bit depending on humidity averages, etc. But overall, the AC indoor coil will be sized for that cooling load loss and a 15 degF delta. The furnace, on the other hand, will have to make up a 60 degF delta (70-10) at that same BTU/hr loss. So the furnace has to supply many more BTUs to overcome the loss rate. Whereas the indoor coil may have to provide up to 22k BTUs/hr, the furnace may have to provide 68k BTUs/hr. These are generalizations for the example, but you get the idea. Also, the condensing and evap processes move from side to side in HP whereas they are set in AC. With a HP system, you evaporate inside in summer, but you condense inside in winter. There are all kinds of nuances that are different between the two concepts and the application of different coils and their operational parameters.
Now, if you take away the furnace system and now decide you want a HP system, that indoor AC coil which only had to supply 22k BTUs/hr in summer, now has to supply 68k BTUs/hr in winter. Suddenly that smaller indoor cooling coil is not large enough to be an indoor heating coil. So in HP systems, the HP indoor coil is typically larger because it has to make up a larger delta-T loss.
Soooooooo ....
My point in the OPs quest is that he had already purchased a heating system based on a traditional Furnace/AC concept, and therefore the indoor coil is undersized for the heating need (especially in ND !!!). Add to that, we understand the fact that he now has made us aware that he had bought a new indoor coil along with the furnace. So if he wants to change to a HP concept after the fact, he not only is wasting the use of the furnace, but he also is going to have to toss out a brand new undersized indoor coil in favor of an indoor coil that is large enough to do heating in addition to cooling.
Now do your cost analysis. Yes, often electricity can be cheaper in a "per hour" use factor. But if you now throw in a furnce that won't be used much at all (wasted money spent) and a brand new indoor coil tossed in the trash (lots more wasted money spent), and the purchase of a larger indoor coil (more money spent), and the need to modify the ductwork for the new larger indoor coil ... welll ..... you get the picture now?????
If you want a dual-fuel or HP system, you have to commit to that concept up front. You cannot do it after the fact; you'll NEVER recoup the costs associated with modifying the systems in retrospect with the supposed "savings" of using a HP. When you toss thousands of dollars in the garbage because you bought a system that won't provide what you need, the ROI of the HP savings is urinated away very, very quickly.
- HP systems make excellent sense in warm and moderate temps (above 40F) as they are very efficient
- HP systems can work decently in cold temps (above 25F) as they are moderately efficient
- HP systems struggle in ever colder temps (below 25F). (Its not that they don't work; it's that they defrost often and use heat packs which are not nearly as efficient as the HP process; the colder it gets the more they defrost and the more they rely on the "kicker heat" aka toaster coils).
- HP systems will NEVER make sense when you try to bastardize a new Furnace/AC system into something it wasn't designed to be.
That's my take on it.
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So in theory, given the above info, purely hypothetically speaking: an existing "small" indoor coil matched for A/C may work with a HP assuming the HP is only used when the Delta is smaller, like during the transition seasons and the NG furnace is "aux" heat that is used nearly 100% of the time during the actual winter months. Just curious if this even exists as a setup used anywhere or not...I know most HP users have electric for aux heat and it is truly "aux" by definition.
May also want to read and understand the elegance of inverter Direct Current type heatpumps vs traditional old start-stop style Alternating Current Heat Pumps
https://www.daikin.co.nz/articles/what-inverter-heat-pump-and-why-do-i-need-one
https://www.daikin.co.nz/articles/what-inverter-heat-pump-and-why-do-i-need-one
New heat pumps work perfectly fine in cold climates and can save you huge money on heating bills.
dnewton3
Staff member
That is what's often referred to as a "mini-split" system. The effeciency of those and effectiveness of those are getting pretty decent.
HOWEVER ... that's not what the OP has. He has a traditional Furnace/AC system and he would have been considering a traditional HP system conversion. And so that's where my advice was targeted. And stand firm on my advice; it would have been a very poor decision to convert UNDER THE CIRCUMSTANCES of his specific situation. And that goes for anyone who would be in a similar situation.
There are some good advancements in HP tech, improving with each iteration. But, those improvements are often not without problems. These first generation of inverter systems are having very spotty reliability. Like most leading edge tech, they rely on tech that's great in theory but often manufacturing systems have not caught up with the implementation of that tech well enough to make for high-quality products.
And, HP systems bring with them challenges that are not as easy to overcome as traditional gas-fired systems. For example, my high-eff furnace only takes about 10 amps to fire off and runs on about 7 amps. Any small generator can easily power my furnace in an emergency if the electricity goes out. But if the electricity goes out, you'd need a MUCH larger generator to power a HP system versus a gas-fired system. In summer, if you go without AC, you'd most likely live to see another day. But in winter, if you go without heat for long, you'll freeze. It is much easier to sustain life when it's hot outside than when it's cold outside. My point is that any typical system requires electricity to operate, but a gas-fiired system takes far less to operate. A traditional gas-fired system may not be as "efficient" on a dollar-for-energy basis, but they take less electricity to run on a "total use" basis. Gas fired units only take their max amp draw during the phase when the HSI (hot surface ignition) system is activated. After that goes off, it's just a PCB holding the gas valve open and a blower (typically ECM or VS). But HPs have to run both the indoor and outdoor units in all phases, and with the added bonus of major amp draws when the aux heat (coil packs) come on! A typical gas-fired furnace can run easily on a 15 amp rated line, and typically will pull less than 10 amps when running. But most HPs (depending upon size) need a LOT more amperage to run, especially when the heat packs are on. It may be more efficient in a "dollar basis" to run a HP, but it is NOT more efficient to run a HP in terms of total kW consumed, hour for hour of operation, contrasted to a gas furnace. If you're paying for the electricity via your normal bill, then the HP seems a great idea. If your electrical source fails and you have to generate your own power, you'll be cursing your HP as it sits idle because you don't have a 40kW generator at your beckoning.
Further, IMO there is no way, right now, that our national electric grid could handle the entire nation being on HPs; it's already on the brink as it is. If we were to add eschew all gas-fired systems and implement HPs across the nation and we'll be living in the dark ages from constant blackouts. It's not uncommon to see black-outs and rolling brown-outs in major metro areas in summer due to cooling demands right now. Well, if you run those same systems in winter, you'll get just as many power-outages and probably more, because HPs draw more power in heating mode than cooling mode, and the colder it gets, the more they need power to meet demand.
HPs are a great tool for some circumstances. They are not a one-size-fits-all solution for everything.
Did you mean $0.35 per therm or $3.50 per therm. To convert therms to 1,000 ft you multiply by about 10. That would compute to $3.50 per 1000 ft3. Here is a screen shot showing the residential price of natural gas in North Dakota is at least $27.32 per 1000 ft3.
Sorry to bother you. I realize your project is all done and it’s a moot point, but as you can see your original thread has grown. I’m a supporter of heat pumps in northern climates when a person is about to buy a new AC unit anyway. Maybe in your next house! So, if you can clarify your natural gas cost it might help someone else. Thanks.
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