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Shut down the heat pump below 0 degrees?

bczoom

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I always hear about the inefficiency of heat pumps in below freezing temps but mine keeps chugging away.

At about 30 degrees, temps at the registers coming into the rooms are 90°+.

Fired it up last week at 0° and it was still pushing 80°.

Well, it's going below -10° tonight. No idea what the heat pump will do.

I hate to switch the furnace to EMER heat knowing how much electricity those heat strips in the air handler use.

The furnace is secondary heat. I have 2 wood stoves running which can handle our heating needs so long as I keep wood in them. I'm thinking of the wee-hours of the morning when the stoves die down.
 

Kane

New member
I dunno, zoom. You must have one magical heat pump. I could be wrong, but even a newer high SEER unit would struggle to do a delta of 35-38 degrees. Are you sure?

Some units will light up just a portion of the auxiliary heat strips when demanded without signifying it's going into full EH.
 

bczoom

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I thought about it being magical as well.

On the heat strips, I thought about that but discounted it since it was blowing 90° when it was 30° outside and only 80° when it was 0° outside. I'd have thought if the strips were in play, it would blow hotter when it was 0°.

It has one of those newfangled thermostats that I have to use the manual on if I want to do anything besides raise or lower the temp. I did go through the motions today of switching it to EMER but then put it back to normal heat.

Speaking of magical and that thermostat, I read that you can set it to AUTO and it'll switch between A/C and heat on its own. I've wanted that option several times since in the spring and fall, both are used in the same day.
 

XeVfTEUtaAqJHTqq

Master of Distraction
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Are the heat strips that much more inefficient than a regular electric furnace? I usually switch over to the propane stove when it gets below 20 outside.
 

bczoom

Super Moderator
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As I recall, the heat strips in the furnace are 5KW each and there's 4 of them.

When I got up this morning, the heat pump was running and I had 70° at the registers. I turned up the t-stat and waited awhile. After an hour or so, I was getting 108°. It looks like the t-stat allows the heat pump to try to get it up to temps but if it doesn't do it, it kicks on the heat strips.
 

Kane

New member
Again, an efficient heat pump is doing well to provide a 30 degree delta, heat or cool. Beyond that ... Northern homes should design in the most efficient supplement, be it electric, gas, oil or wood.

I always liked oil, personally, when I lived in the God forsaken regions north of the 31st parallel.
 

bczoom

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Does the size of the heat pump change that 30 degree?

I have a 5-ton and I get better than the 30° on the A/C side as well.
 

squerly

Supported Ben Carson
GOLD Site Supporter
Man, I hate it for ya fellas. An Outdoor Wood Furnace pushing hot water through a radiant floor system is the way to go! Looks like I'm spending about $3.60 a month on the electricity to run the pumps. :clap: It was -7 outside this AM but it was a nice toasty 73 inside.

I'm burning about a 1/2 cord of wood a month, which I have to cut of course, but I don't mind cutting. Makes me feel good and alive after cutting for a few hours. And the radiant heat is uniform too, it's the same temp on one side of the room as it is on the other, very unlike a interior wood burning stove.
 

BigAl

Gone But Not Forgotten
SUPER Site Supporter
How the hell can you afford to pay the electric bill ?? Those heat pumps eat major electric in really cold climates .
They use to be real popular everywhere back in the 60's and 70's . Now you can't give one away . Nobody wants em .
 

bczoom

Super Moderator
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How the hell can you afford to pay the electric bill ?? Those heat pumps eat major electric in really cold climates .
They're not bad on electric. I figured it out once and it costs about $1 per day to use it.

I use the wood stove(s) for my primary heat in the winter so the heat pump only comes on at night or on really cold days but my electric bill doesn't really change from summer to winter.

Our house is all-electric and our bill runs about $140-150 per month.
 

muleman

Gone But Not Forgotten
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I think you will find that your air handler is simply transfering the heat from your stoves throughout the house. Below 40F there is very little heat in the air to transfer into the house. At todays temps there ain't any. I would replace the heating strips with a hot water coil and a small propane boiler to heat it. The indicator light for the electric elements is generally powered off the same contactor that energizes the elements. When the light is on the meter is cranking.
 

Kane

New member
The rule of thumb for a typical split system says that: above 30 degreeF outside air, the system can provide comfort without supplemental heat. Below 30 degreeF OA, comfort requires supplemental heat. But right around 0 degreeF outside air, the system will provide no useful benefit.

Sorry.

When comparing the performance of heat pumps, it is best to avoid the word "efficiency", which has a very specific thermodynamic definition. The term coefficient of performance (COP) is used to describe the ratio of useful heat movement per work input. Most vapor-compression heat pumps use electrically powered motors for their work input. However, in many vehicle applications, mechanical energy from an internal combustion engine provides the needed work.
When used for heating a building on a mild day, for example 10 °C, a typical air-source heat pump (ASHP) has a COP of 3 to 4, whereas an electrical resistance heater has a COP of 1.0. That is, one joule of electrical energy will cause a resistance heater to produce only one joule of useful heat, while under ideal conditions, one joule of electrical energy can cause a heat pump to move much more than one joule of heat from a cooler place to a warmer place. Note that an air source heat pump is more efficient in hotter climates than cooler ones, so when the weather is much warmer the unit will perform with a higher COP (as it has less work to do). Conversely in extreme cold weather the COP approaches 1. Thus when there is a wide temperature differential between the hot and cold reservoirs, the COP is lower (worse).
On the other hand, ground-source heat pumps (GSHP) benefit from the moderated temperature underground, as the ground acts naturally as a store of thermal energy.[4] Their year-round COP is therefore normally in the range of 2.5 to 5.0.
When there is a high temperature differential on a cold day, (e.g., when an air-source heat pump is used to heat a house on a cold winter day of 0 °C (32 °F)), it takes more work to move the same amount of heat to indoors than on a mild day. Ultimately, due to Carnot efficiency limits, the heat pump's performance will approach 1.0 as the outdoor-to-indoor temperature difference increases for colder climates (outside temperature gets colder). This typically occurs around −18 °C (0 °F) outdoor temperature for air source heat pumps.
 

bczoom

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I'll read the t-stat manual and see what the light means. As I recall, it changes colors to denote what's running.
 

Kane

New member
Does the size of the heat pump change that 30 degree?

I have a 5-ton and I get better than the 30° on the A/C side as well.
It's not the size so much, but the unit's efficiency rating. A modern high SEER (efficient) unit may give you up to 38 degreeF delta. But, just like anything, a high SEER unit has a high first cost.
 

XeVfTEUtaAqJHTqq

Master of Distraction
Staff member
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I have two high efficiency (~second highest rating whatever that is) heat pumps and they aren't that bad to run most of the time. But it's usually mild where I live. It's nice to have the AC in the summer.

As I said, I just switch over to a big propane stove when it gets cold and a few of those oil filled radiators in selected places and my bills are reasonable. Not enough to warrant the expense of putting in a wood fireplace/stove.
 

bczoom

Super Moderator
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I shut the heat pump down and switched it to emergency heat. Still don't have the balls to go watch the meter spinning on the outside of the house.

Wood stoves are kept running hot so the furnace doesn't kick on much.
 

jwstewar

Active member
I have our heat pump set to switch over to propane at 25 degrees. Now the other night when it was -9 and the wind was howling our upstairs was still chilly (first floor was 73). So I went to our living room and turned on the vent free fireplace. The way the house is laid out all of the heat from that comes out of the room and right up the open stair case. My daughter's room got so hot she had to turn on her ceiling fan. Oooops, guess I had it cranked a little too high.:whistling:
 

Dargo

Like a bad penny...
GOLD Site Supporter
I shut the heat pump down and switched it to emergency heat. Still don't have the balls to go watch the meter spinning on the outside of the house.

Wood stoves are kept running hot so the furnace doesn't kick on much.

I've kept our wood burner going for almost a week now. My units are NG and 93% + efficient each, but I have 3 of them running to heat (and 3 A/C units; a 3, 4 and 5 ton) my place. Really cold winter months are bad, but not as bad as extremely hot summer months. I've had utility bills crack 4 digits a few times. :doh:

Glad to hear your setup is working for you. I have thought about going geothermal, but the last time I got a quote for moving everything over to that it was over $50k! :eek:
 

Kane

New member
I've kept our wood burner going for almost a week now. My units are NG and 93% + efficient each, but I have 3 of them running to heat (and 3 A/C units; a 3, 4 and 5 ton) my place. Really cold winter months are bad, but not as bad as extremely hot summer months. I've had utility bills crack 4 digits a few times. :doh:
Holy shit, Dargo! That sux. How many square feet are you trying to condition?
 

Dargo

Like a bad penny...
GOLD Site Supporter
Holy shit, Dargo! That sux. How many square feet are you trying to condition?

Um, remember, I do have 5 kids. It's north of 7500, and I have all the insulation I can get in the attic along with 6" insulated interior and exterior walls with brick on the outside. Just a whole lot of air to control. :sad:

P.S. The 6" insulated interior walls was the best thing I ever did with a large family who always has several friends over! I literally cannot hear much past the next room no matter what they are doing; which is sometimes a bad thing...
 

bczoom

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Well, i turned off the heat pump during those cold snaps and ran off emergency heat. With the wood stoves running, they pretty much kept up and the furnace only ran short periods during the day.

Here's the electric bill. Didn't seem to change too much. About $70-80 more to cover a screaming cold January.

02/04/2014 $151.42 1,779 Actual
01/08/2014 $231.79 2,696 Estimated
12/05/2013 $148.34 1,692 Actual
11/04/2013 $134.62 1,529 Estimated
10/07/2013 $141.09 1,609 Estimated
09/05/2013 $160.03 1,624 Actual
 

Dargo

Like a bad penny...
GOLD Site Supporter
Well, i turned off the heat pump during those cold snaps and ran off emergency heat. With the wood stoves running, they pretty much kept up and the furnace only ran short periods during the day.

Here's the electric bill. Didn't seem to change too much. About $70-80 more to cover a screaming cold January.

02/04/2014 $151.42 1,779 Actual
01/08/2014 $231.79 2,696 Estimated
12/05/2013 $148.34 1,692 Actual
11/04/2013 $134.62 1,529 Estimated
10/07/2013 $141.09 1,609 Estimated
09/05/2013 $160.03 1,624 Actual

Unfortunately, I live where we have some of the highest utility rates in the country. I haven't seen utility bills like that since college days! Your bills would be higher than that here if you lived in a 10'X15' yard barn, with no windows, and 3' of insulation around it and under it!
 

Doc

Bottoms Up
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Well, i turned off the heat pump during those cold snaps and ran off emergency heat. With the wood stoves running, they pretty much kept up and the furnace only ran short periods during the day.

Here's the electric bill. Didn't seem to change too much. About $70-80 more to cover a screaming cold January.

02/04/2014 $151.42 1,779 Actual
01/08/2014 $231.79 2,696 Estimated
12/05/2013 $148.34 1,692 Actual
11/04/2013 $134.62 1,529 Estimated
10/07/2013 $141.09 1,609 Estimated
09/05/2013 $160.03 1,624 Actual
I heat with gas and my electric bills are still that high. Over $200 the past two month. :angry:
 

bczoom

Super Moderator
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I'm happy.

I have an all-electric house with 2 kids tapping. Friggin kids suck up 1/2 of the power (or so I think)
 
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