Heat pump or wood stove

"@ Simonkenton, if you have a new heat pump that isn't working well, you should probably have somebody take a look at it. There's no reason a properly sized heat pump should not keep a house at a comfortable temperature."

Twenty years ago, I lived down in central Georgia. Georgia Power was pushing people to get heat pumps and would give a $400 cash rebate if you put one in.
Gee, why would they give all that money away? Because if you bought one, they had you, winter and summer, and they knew they would get their money back, and then some.
I knew lots of people who had heat pumps and nobody was happy with them in cold weather, down there, 15 degrees was a really cold day in January. These people ran up massive power bills in winter, and wished they had central gas heat. Propane is not too expensive down here in the southeast.
However, these people were happy with their heat pumps in August, when it is 98 degrees, said they were good for a/c.

My fiancee bought a nice big brick ranch style house in Asheville NC several years ago. It had a heat pump, probably installed in 1993, that thing was a piece of crap and the tenants had massive power bills, always complaining about the house being cold.
That POS crapped out 3 years ago. We have a very good heating and air company, because Shirley has 4 nice big rental houses here in Asheville. Our heat and a/c company recommended replacement with a new heat pump, claimed performance was way up etc etc. I now suspect our heating and air company got a cash rebate from the electric company, otherwise I don't know why they would have urged us to get this new heat pump.

We were inclined to go with central gas furnace instead but let this guy talk us into the heat pump. Biggest mistake we ever made, it is the same story I knew so well back in central Georgia, except, Asheville is, day in and day out, 20 degrees colder than central Georgia.
Tenants complain that the house is not warm enough, and they run up massive power bills. We get the heat and air company out there 3 or 4 times every winter, to see what is wrong, etc etc. They will replace a thermostat one month, or they will adjust something the next month, but it is always the same story.

Now, this is not a geothermal heat pump, I am talking about a straight electric heat pump.
If y'all are happy with your heat pumps, God Bless You. I have been involved in the construction trades for 45 years, I have helped manage 5 nice rental houses for 25 years and I have seen all I want to know about heat pumps.

Our other 3 rental houses in Asheville all have central gas heat. We get no complaints from tenants, their houses are warm and gas bills are reasonable. All four of these houses are similar, almost indentical, ranch style houses built in the sixties with lots of retro fit attic insulation.




Our Asheville house with the demonic heat pump. Need to get an exorcist to come out and cleanse the house of this heat pump.

Rely on the heat pump in shoulder season, running the stove to break the chill if needed/wanted and have the wood. We have a heat pump and gas furnace. Heat pump works great for a/c, but don't care for it for heat. We have it set to not run at about 38 degrees or lower, gas kicks in. We found when we built this house and propane was under a dollar a gallon, that if we simply ran the wood stove the coldest 2-3 weeks we took the biggest bite out of the propane useage. Now that propane has gone up, we run the stove as much as possible, but I don't mind the furnace kicking on occasionally, and don't burn wood when it gets above 50 during the day.

The biggest problem you will have is that during the shoulder season, that heat pump will be kicking on when it is least efficient, in the early morning cold periods. I would be doing anything I could to keep those backup heat strips from kicking on. Maybe even some well placed space heaters might work better than lighting a small fire every day and would probably be more efficient than the heat strips.

Portable electric heaters aren't more efficient than strip heaters. The only difference would be that you zone heat with a portable heater or in other words just heat the room that is occupied.

realstihl said:

Portable electric heaters aren't more efficient than strip heaters. The only difference would be that you zone heat with a portable heater or in other words just heat the room that is occupied.

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True, but when you look at the total system energy that goes into ASHP's, I would argue that point of use electric may be more efficient during low outdoor temps. Although the COP for the refrigerant system should always be above 1, that value may be neglecting the fan and defrost energy. You get a lot less value out of your system's (1/2, 3/4, or 1 HP) blower, when it's being used to move around 74 degree air vs. 90+ degree air.

I have a 2.5 ton Lennox heat pump, for the basement and first floor and another for the second. The basement and first floor are zoned separately. The heat pump runs above 28 degrees and propane backup runs below 28 degrees. In Connecticut it does a good job, it puts out 70 degree air. The only thing it takes care of is the basement unless we're away, the king takes care of the first and second floors.

If you can get natural gas, get it. It's cheap enough, especially at current prices, an air source heat pump only saves a small amount of money in mild weather, and can potentially be more expensive in cold weather, even before your auxiliary heat kicks in.

realstihl said:

Portable electric heaters aren't more efficient than strip heaters. The only difference would be that you zone heat with a portable heater or in other words just heat the room that is occupied.

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If you have an electric furnace, depending how good your ducts are, unless they're inside the insulated volume of the home, you can expect to lose in the ballpark of 20-40% of the energy from the ducts. So portable heaters and baseboard heaters come out ahead in that situation even before you factor in zonal management, which gives you even bigger savings. On the downside, a non-trivial number of people get careless with portable heaters and start a fire.

brant2000 said:

True, but when you look at the total system energy that goes into ASHP's, I would argue that point of use electric may be more efficient during low outdoor temps. Although the COP for the refrigerant system should always be above 1, that value may be neglecting the fan and defrost energy.

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During low outdoor temperatures, possibly. If you auxiliary heat is coming on definitely. COP actually can drop below 1. This usually doesn't happen until around 0deg F, but your aux heat probably came on well before that.

The heating season performance factor takes into account energy consumed during defrost and warmup, also including, as I understand it, the fan power and auxiliary heat at low temperatures (I've only skimmed the standard here). In cold climates, however, the normal HSPF rating isn't useful because seasonal performance deviates too much in those cases from the single rated value. It also does not take into account duct losses.

To tie all this together, I'll use some figures from the spec sheet for my HSPF 9.5 heat pump. At 47 degree outdoor temp and 70 degrees indoors (the AHRI rating temperatures that approximate the average heating season conditions in mild climates), it has a steady state COP of 4.21. However, the HSPF of 9.5 correlates to a COP of 2.78 - over the whole heating season, I should expect to average only about 2/3 the steady state performance, but still much better than resistance heat.

If I factor in 20% duct loss, my true seasonal COP should be in the ballpark of 2.2. I think the full system COP would drop below 1 somewhere around 5-10 degrees. So theoretically, it's cheaper to run the heat pump than the strips if it's warmer than that, but it doesn't matter, because my heat loss exceeds the heat pump capacity at around 30 degrees.