Normaly heat pumps are not as efficient at this low of temperatures. You might want to consider installing outdoor temperature sensors on both of the units so the sensors will let thermostat know when to block the heat pump and turn on back up heat. I don't know which thermostat you currently have to controll you system Honeywell 8000 should work great with the sensors.

Here is a link that might be useful: Brothers Heating home site

Your comments are common from folks using a heat pump for the first time. Although the air is warm, it isn't like what you would be used to with gas oil or electric heat. At the temperature you described, your heat pump was probably providing heat at the same rate your home was losing it thus it ran constantly. That says a lot for the unit itself but surely doesn't necessarily feel comfortable as well as may cost you more in energy usage (although not necessarily always). BROTHERSHEATING provided a sound solution for lower temperature areas such as yours and CREEK SIDE provided you with great information too that supports that.

At 10F ambient, my 3-ton 9 HSPF Goodman heat pump has a C.O.P of 2.26.

That means it's still 226% cheaper to run than straight electric resistance heat, even at 10F ambient.

As the heat pump runs continuously, a good digital thermostat (like my VisionPro 8320) will cycle the auxiliary electric strip heat on/off to help the heat pump maintain the indoor setpoint.

If you don't mind a very high electric bill for winter heating, shut the heat pump off and run strip heat only.

I would recommend letting the heat pump run if you have aux electric heat. If you have a gas furnace as aux heat, that's another story.

Take care.

Gary you forgot to mention making sure the strips are staged otherwise the very cold weather efficiency goes in the toilet compared to a properly staged unit if it has electric heat.

This may help! I just completed testing setback vs continuous temp settings and came up with the following.

Our high for the past couple days hasn't even been half of that. -16 for a low tonight and -3 for a high tomorrow is predicted tomorrow. "This place doesn't seem to have a temperature" Is it spring yet?

In my short experience of having a duel fuel setup and playing around with my heat pump I noticed the following.

The heat pump does best at maintaining temperature. It doesn't do so great it bringing temperature up.

The stats that countryboymo says above sound very realistic too me.

Thanks for all the great information. I messed with the thermostat some and even if I set it at 70 or 72, it kept it there and ran continually. Finally, yesterday, I set it at 74, and it did turn to the auxiliary backup heat. I have never seen it do that before, so I wasn't sure if it would, but it did and showed it on the thermostat. I guess it is actually working correctly. I'm not looking forward to the electric bill next month, but it seems to be keeping everything warm enough. Thank you for all the great input and advice!

I forgot to mention that I found the information about moving the temperature down and up very informative. I have always wondered about that, because it does seem to take a lot of work to bring it back up to temperature once it has cooled down. That is a HUGE difference. Our current thermostat is not programmable, but we used to have one and wondered about that. We used to have it cool off in the winter during the day, but in the summer we kept it constant...otherwise it was trying to cool off the house during the hottest part of the day.

That's very good info. I posted a similar question on HVAC Talk but haven't gotten a response yet, although a couple pros alluded to the fact constant was better at colder temps than setbacks.

I changed my setbacks shortly after the home was built from the "Energy Saving" 5 degrees to 3 degrees. Saved a little money, I think but couldn't be sure. This, however, makes very good sense.

I do wonder if the results would be noticeable enough at higher temps say in the mid 40s and beyond.

Caymandiver75, it's nice you gave us as close to an apples-to-apples comparrison as possible. I personally appreciate that. Wish you had posted in late November before we got the nasty December freezies here in Olympia, Wash. We had some record cold for this part of the country.

I have my heat pump set to run down to 20 degrees and the natural gas furnace locked out until 25 degrees. My furnace and HP are both at break even at 17 degrees. My exterior thermostat usually read about 2 degrees higher than it really is because of the insulation material around it. (I asked the installer where it was and he showed me) So... when the T-stat reads 20 it's really about 18 outside. My Honeywell IAQ only is adjustable in 5 degree increments.

The Honeywell IAQ outdoor temperature sensor is supposed to be mounted in free air where the sun can't possibly shine on it. Under an eave is suggested by Honeywell.

Installers seem to like to place them at the outside unit, which is the wrong place. High readings are the result.

I agree, Creek Side, but unfortunately, they put it where the sun does shine. In the summer after 11 a.m. and the sun is shining on the south side of the home where the heat pump is, I can just forget about accurate readings until about 7 p.m.

CaymanDiver 75, one other thing on your readings... did you do anything majorly different between the two days, such as a couple loads of laundry? I write my KWH readings down daily (very anal, yes I agree) and noticed that New Years Day I used 70 KWH with highs of 50 and lows of 42 with 19 HDD (heating degree days). January 2 reading was 59 KWH with highs of 49 and lows of 42 with 19 HDD.

Just curious if something like that happened with you.

A test like that is not accurate unless the parameters are tightly controlled and all contributing factors noted. The meter reading includes all household electric use, not just the heat pump. Cooking? Bathing? Dishwashing? Laundry? Sunshine vs. overcast? Wet vs. dry weather (affects heat pump defrost frequency)? Did the 3°F recovery involve use of auxiliary heat strips?

2°F and 3°F setback is very minimal. More savings is potentially garnered with larger setbacks. I'm in TX. We had a rare snowfall during a wet norther on Dec 4. After that Dec 4 weather incident, I didn't run the central heating (heat pump) for several weeks. Instead, I used a space heater only in the bedroom at night. I noted that even with occasional nighttime temps into the upper 30°Fs, the unheated rooms in my house rarely dropped below 60°F. So ... if I had been running the heat pump at 70°F normal with a 2°F setback (68°F), it still would run to maintain 68°F during the setback periods ... but an 8°F to 10°F setback (setpoint of 62°F or 60°F), it would run very little during the setback periods, if at all. That'd make a difference on KWH usage in regards to setback vs. none.

The setback makes more difference in some areas than others. Here In west central Mo it has been close to the single digits at night and mid teens during the day. I stopped my setbacks when this cold snap hit. In the worst of winter if you set the stat back 3 degrees and its supposed to pick that 3 back up before you get home at say 5pm. Its already dropping temp outside and almost dark and trying to come up 3 degrees of which it probably started trying for at hopefully noon if there is an outdoor temp sensor. I just don't see it to be very useful to do a set back when its so blasted cold unless I let it drop at bedtime and left it there till noon or 1 so the heat pump could bring it back when its warming up and hopefully sunny rather than wait till 4-5pm.

The problem with using setbacks with a heat pump is that the heat pump does not have enough btu output to recover from the setback during brutally cold weather (the btu output of the pump drops by half at 15F). This requires aux heat to be used to recover from the setback temp. Bad news for people like me with auxiliary electric strips.

Setbacks are OK at 45F ambient or so, but not at 20F (for example).

I agree, Creek Side, but unfortunately, they put it where the sun does shine. In the summer after 11 a.m. and the sun is shining on the south side of the home where the heat pump is, I can just forget about accurate readings until about 7 p.m. -- speedymonk

They put ours by the heat pump too, using spare wires in the cable connecting the heat pump to the air handler. Doing so explicitly violated Honeywell's installation instructions.

The outdoor temperature sensor is supposed to have its own isolated wiring. The instructions warn against running the sensor wire bundled with other wiring of any type. There is absolutely no need to have it located at the heat pump. In fact it is a bad place for it because of ground proximity and heat thrown of by the heat pump.

It simply needs to be located outside the home several feet above the ground in free air and complete shade at all times. The system will not perform properly if the outside temperature is not sensed accurately.

I plan on relocating the sensor, once we get moved in.

Thanks for all the comments, but I am a little confused. I have electric heat In a summer home, that isn’t used in the winter. I’ve been setting the tstat at 50 while not there.

I have heat strips (emc heat) and I have a compressor (Heat setting)

Which one costs more to run when temps average near zero or below ?

Does running the compressor heat result in the extra wear and tear of the ac unit, requiring sooner replacement?

While it may cost more to run using heat strips, wouldn’t it save wear and tear?

odd that the upstairs heatpump would be running continuously. If it was the downstairs heatpump that is understandable since heat rises and goes to the top of the house. check where you are losing heat from the upstairs. e.g. openings in the ceiling sheetrock (recess lights, fire sprinkler heads) that may not be properly sealed, inadequate Attic insulation.

On my Honeywell thermostat..if I increase the temp by 2 degrees, the heat pump will run, however, if I set it with an increase of 3 degrees or more, the electric back up will automatically kick in.

I read that heat pumps usually run all of the time. They maintain a constant heat rather than the swings of the temperature of a gas furnace needing to drop to a certain degree before the heater runs to a degree or two higher. You want to buy a heat pump that is quiet and multi-speed as it runs all of the time. Lower speeds on a multispeed are normally quieter. If you have solar and freezing weather only happens a couple times a decade, heat pumps make sense.

Heat pumps do not run "all the time!"

They can run for long periods in instances of weather extremes when sized closely to the load requirement. My 2-stage system ran continuously for two days in several instances of sub-30°F (to 23°F) weather. Low stage majority of the time, brief periods of high stage. Auxiliary/backup is on a 3°F differential and never engaged, I would notice it.

My mother has a variable-speed system. I can monitor it remotely. The fancy-smanchy thermostat tracks operational statistics. Yesterday in the heat of the afternoon, cooling run-time for the hourly periods from 1p to 7p. Not continuous but nearly so. That's on a 15°F to 18°F differential for indoor vs. outdoor temp. It'll get "worse" as the summer heat intensifies. What would happen on 40°F indoor/outdoor differential (or more) during a winter cold snap?

1p = 45 mins, 31.8% capacity

2p = 54 mins, 38.8%

3p = 60 mins, 43.5%

4p = 57 mins, 40.8%

5p = 57 mins, 40.7%

6p = 60 mins, 45%

7p = 50 mins, 35.9%