Heat Pump in Northern Climates?

tbm5690

tbm5690

Joined
Apr 28, 2020
Messages
1,435
Location
North Dakota
Hi All,

Just replaced my NG furnace with a 2-stage variable speed 96% AFUE unit. Now it's time to replace the outside AC coil, and I'm curious if I should also consider a heat pump for a dual-fuel set-up. My gas rate is $0.35/therm and my electric rate is $0.10/KWh, but I believe I could get better on an off-peak rate. I live in ND where temps routinely can stay below 0 for weeks in the winter, and we can hit low 90s at times in the summer. Would the extra cost for a heat pump over an A/C unit be warranted in my case for the swing seasons, or just stick with my highly efficient furnace/cheap gas rate for all my heating needs?

For what it's worth: house is 2400sq. feet and pretty well sealed and insulated. Gas bill last month with an average temp of 9F was $80, which includes keeping my 600sq. ft garage heated at 50 degrees as well.
 
I’m shocked you’re even considering an air to air heat pump to provide heat in ND. Maybe I’m not understanding what you’re proposing. In Virginia Beach, where it rarely gets below 30 above zero, we save money with a gas furnace/heat pump combo.

Unless you’re going to put in a ground loop for the heat exchanger, you can’t get enough heat from the below freezing air to heat your house with just a heat pump, and at that point, the “aux heat” which is an electric grid in the duct, kicks in to supplement.

The gas furnace/heat pump combo works better for us in our mild winters than a heat pump only set up.

With a ground cooling loop (buried below your frost line) it’s a different story, but the installation on that requires a lot of digging. It isn’t cheap.

Since you’ve got gas, stick with a gas furnace. Absolutely.
 
What's the extra cost to add the heat pump vs. a standard AC? I'd be very surprised if you broke even in North Dakota, assuming cheap natural gas, but it would buy you some future flexibility regarding rates. Anecdotally, I've seen a fair amount of heat pumps in Nebraska, more to the south in Missouri, but relatively few north of that (much of my experience being in Minnesota). My aunt and uncle have one that they keep locked out all winter because they don't care for the type of heat it puts out (relatively "cool" heat and it runs for long periods); they simply use the gas furnace for all their heating needs. If you didn't have inexpensive natural gas available, and were on propane or resistance heat, they make more sense. (When we got a new furnace and AC in 2010 in southern MN, no one even mentioned heat pumps.) But for someone in an extreme climate like North Dakota with $80 gas bills in the dead of winter, there really isn't much room for improvement.

Here's my rough geographical guess for the Great Plains/Midwest - heat pumps make a good bit of sense below I-70, probably make sense between I-70 and I-80, and likely aren't too much help north of I-80, assuming that you're on cheap natural gas.
 
I paid extra for the heat pump on the A/C at my last house. We like the house cold, so by the time the house was cold enough to use it, the outside temp was too cold to use it. Didn't work out for us.
 
Thanks for the replies. Astro, gas furnace is staying 100% and would be used most of the winter...technically this would be my "aux" but in reality primary from November-February. It's the Spring and Fall months where I'm questioning the worth of letting a heat pump do the work where it's 40-60 degrees out or so. Not interested in the cost to put in geothermal. Sounds like sticking with a traditional AC unit gas furnace combo is the way to go.
 
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Are you replacing the whole ac or just the coil outside? If I understand correctly you will likely toss out the whole AC if you want heat pump but you can just "replace the coil" and recharge if you only want to replace the coil. You won't break even in this case.

Your gas is very cheap, and your electricity is also cheap but not as good as gas. I'd just use the gas furnace and leave AC alone, fix what is needed only.
 
I'm not all that far from North Dakota: above the border and north of Idaho. I built a house in 2012. I opted for the air to air heat pump option. I was already planning on central AC anyway. It added a bit of cost, so once you've decided to have AC, going to a heat pump is an OK decision. If you weren't going to have AC, then going to a heat pump is a big decision.

My power at the high incremental rate is equivalent to 10 cents per kwhr US. I heat with propane since natural gas is not tied into this rural mountainous area which is another reason to swing towards a heat pump; heating fuel is expensive.

My heat pump operates at 40 F and above. I find right now, I coast all night with the furnace off, and it comes on in the morning and warms the house up to 70 F using a propane boiler and air heat exchanger. When the outside temp rises to 40 F before noon, the heat pump heats the house all afternoon until 5:00 PM, when I coast again most of the night depending on outdoor temperatures.

So basically the heat pump does not operate below 40 F, so it is useless for me between December 1 and mid Feb, which is 2-1/2 months but it is what heats the house from mid Feb until about June 1 and again in September, October and most of of November.

I'd only recommend the heat pump in colder climates for folks who had a large central air conditioner planned for the summer. We run AC from June through to the end of September, operating 18 hours per day, roughly, during July and August . Hope that helps.
 
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Some of the newer high efficiency heat pumps have a lot of coil and an intelligent defrost, they can produce considerable heat a 0F. Not as good as a gas furnace though. The vendors have charts, the seller installer should be able to get them and explain them to you. Ductwork losses can be considerable too, the newer ductless units are more efficient, make more noise and some folks find them ugly. A competent contractor should be able to tell you in $$ how much you might save.

Rod.
 
From what I remember of having a heat pump years ago, was the temperature of the air coming out of the vents was only room temperature at best. If felt like a constant draft, and the thing ran almost continuously so I don't see what energy savings they provide. In cold climates the emergency heat will come on often and raise your electric bill considerably.
 
I have a gas furnace with an AC unit that also has a heat pump. I never use it below 45 or so, it simply runs way too much when it's colder than that.
Click to expand...
I did the exact same thing in Southern Ohio and was very happy with the setup. One thing though is that we added a wood burning fireplace insert for the coldest days. The fact that the heat pump ran the indoor fan longer actually turned out to be a plus when we had a fire in the fireplace. It would distribute the heat throughout the house and everything was cozy.
There is no "resistance heat backup" in these installations, the backup is the gas furnace.
I think the key to making this work is that the thermostat be VERY customizeable since you'll need to tweak a lot of settings. The one we had in OH was made by Lennox, and it was perfect for the task. I think my low temp cutoff for the heat pump ended up about 43 or so.
Don't bother with those new "connected" thermostats, they don't give you the control that you need.
An engineer once told me that a heat pump will always be more cost effective than natural gas for heating homes. Resistance heat will eat up all the savings though.
 
atikovi said:
From what I remember of having a heat pump years ago, was the temperature of the air coming out of the vents was only room temperature at best. If felt like a constant draft, and the thing ran almost continuously so I don't see what energy savings they provide. In cold climates the emergency heat will come on often and raise your electric bill considerably.
Click to expand...
I’ll take a temperature tomorrow morning when mine comes on when the outside temp hits 40 F. The low tonight is forecast at 26 F. My “ Emergency” heat is hot water through a heat exchanger in the plenum, heated by a propane boiler. I’ll get a temperature of the air in that mode as well.( yes it is hotter). In my case the word “emergency” is a bit overdone since that’s how it runs across Dec, Jan and Feb when the outside air is way below 40 F.

The reason for the propane boiler is that the floor in the walk-out basement level and the floor in the two car garage are heated with hydronic in-floor heat. It also heats my water heater. :)
 
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I am in Norther Virginia had have a Gas Furnace (95% eff) and a Heat Pump (14SEER 2-speed) for almost 25 years (Yes, the same ones!)
Up until the past 8 years or so the heat pump was cheaper to run down to about 15 degrees. The comfort changeover point was about 20 degrees. When I need a new system it will be downsized but still dual fuel.

With today's natural gas prices it is more like 25-30 degrees for cost now.

With the heat pump I got very long run times, very even temps in the house.
You want long run times for efficiency and comfort.
I think the equipment lasts much longer when not short cycling.

I have added a large amount of insulation and other related improvements (windows/doors/duct sealing) to my house over the years so my 3 ton heat pump is about 1 ton over sized now. The low speed can keep up all summer and until about 25 degrees in the winter. This unit had a low speed of about 60% of high.
 
The OP would have natural gas as auxiliary heat. A heat pump In Maryland would use electric coil heat as auxiliary heat, so the natural gas heat would be way cheaper to operate than coil heat normalized for the temperature difference between North Dakota and Maryland. That’s takes care of the issues for Dec, Jan and December.

It’s important to get the incremental cost of the heat pump vs the air conditioner figured out, then the cost difference between electricity and natural gas. I’ve posted a temperature graph for Minot and it shows that if 40 degrees is used for the cutoff for the heat pump, it will rarely run 24 hrs per day but still it could run for a lot of daytime hours. The availability of natural gas makes it harder to pay off the incremental capital cost of a non-geothermal heat pump.

35F441A1-49FB-4E9B-9752-2E591C79C4AB.png

Ed
 
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As someone in the business I would suggest to stay with just straight AC. Heat pump would make sense if you didn't have natural gas. A dual fuel system like you are talking about it great for people with propane or fuel oil. But with natural gas being pretty cheap it doesn't make economic sense to do dual fuel. The money you would pay for a heat pump would be better spent on a higher efficiency AC condenser.
 
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