school me on heat pumps in single digit temps

jCarroll

Well-known Member
Location
mid-Ohio
Equipment is 7 year old Bryant 90+ propane furnace and matching AC. We've had the property 2 years - it's where my tractor manuals are stored.
The furnace fails to ignite quite often - it tries 4 times, and then goes to sleep for 4 hours to retry. I'm competent at cleaning the flame sensor, burners, etc. To bypass the 4 hours in really cold weather, I turn the 120v power OFF/ON to get it to restart. We're in a week of single digit temps.
I noticed after the IGNITE FAILURE came on, the heat pump was running - at 10 degrees. What can the heat pump do when it's that cold? How does this furnace try to make heat when the room is below set temp, and the auxiliary heat will not come on?
The thermostat is Bryant's Evolution model (it's smarter than I am!)
 
IMHO, HP can use more electricity than it can produce heat. Everytime it defrosts, it's removing heat from house. Get your furnace repaired.

Many where I live go to electric back up not gas.
 
When ours acts up like that all we have to do is call a service man. Then it works perfectly while I pay him to watch it,, Grrr.

Our 10 year old Lennox was doing that now and then when called into use. In fairness it often would go most all winter without the burner running as we have an outdoor wood boiler. Service guy said to run the thermostat up once month to make the furnace light and that would cure it of not lighting when needed. Worked for us.
 
I hope this does not get too long but; Carrier,Bryant,Day and Night and Payne are made by the Carrier Corp. Having worked as an OEM repair, anytime some one has the furnace lock out for 4 hours I look at the traps and drains for clues. Is it plugged? It would drain out over time and run just fine when I appeared only to have it do it when I was gone. Carrier had a recall on the earlier models because the lining in the secondary would come loose and collapse causing the condensate to build up and trip the pressure switches.If there is white particles coming through in the drain, the secondary is failing.Hopefully it is just plugged because it is a newer unit, they need cleaning periodically. A good tech will find it, I did by pulling the draft inducer which can be a big job sometimes, you can see the inside of the secondary somewhat.A heat pump below say 20 degrees costs more to operate than you save due to the temperature differential it takes to create heat and the defrosting needed when it has to defrost as mentioned before me.
 

I usually put my heatpump on emergency heat setting on the thermostat when temps are below 20F. But I have a wood furnace also so the set point on the elect furnace is usually 3-4 degrees below the thermostat on the wood furnace.
 
Is your heat pump geothermal or does it pull heat from the outside air? The geothermal units pull heat from 50F to 60F ground rather than subzero temperature air.
 
Roger, I just heard from a friend in Maine who was talking about heat pumps there. I figured ground source not air, but I was wrong. His folks there have a new air source heat pump, along with an oil furnace they have almost not used this winter. Their last electric bill was only $65. I don't know Maine rates, but that doesn't sound like much electricity.

That heat pump cost $3k to install. I asked what brands performed so well in their cold but haven't yet heard.
 
Saw on the episode of This Old HOuse this week that the old heat pumps would recover heat down to 32 degrees - but the new unit that they installed are supposed to extract heat when outside temp is down to 5 degrees. Not all of the new units have this feature, I think.
 
Ambient air heat pumps work great here in western Washngton, in our usually temperate climate. But on the rare occasions when we get into the teens or single digits, the auxiliary heat strips are working a lot of the time, and I don't believe we're saving much vs. a straight electric furnace.

I haven't heard of units that continue to work well with even colder temps- seems like you're trying to fool Mother Nature. But maybe there is such an animal. I would think you would be better off with underground heat source, or if that's too spendy, propane or natural gas auxiliary heat. Might be worth doing just to get the cooling in the summer, if you don't already have it.
 
You heat pump will work fine in single digits. It may or may not be as cost efficient as propane but it will work--it can get the coils colder than the outside temp and thus extract "heat" from single digit outside temps. Mine does just fine but of course it runs longer.
 
This is probably because the old model heat pumps utitilized R-22. The newer stuff uses the newer R-410(a). . Therefore there is enough head pressures off the top of the compressor to make heat at 0 deg. F. Whereas the old R-22 lost too much heat from head pressures at 0 deg. F.

However, the newer equipment operates at extremely higher head pressures in the summer time causing more horsepower to operate than R-22.

John,PA
 
according to the sales pitch about them removing heat from cold using an air source heat pump I use to think they would be efficient,WRONG! they are ok ? at best to 25 degrees,i got well educated on them after my son installed a new one about 12 years ago,they are nothing but a reverse refrigerant flow unit, ie reversible air conditioner, a good test of how much heat it can get out of cold air is to turn off the electric heat strips inside it when it's is around 20 degrees it can't cycle fast enough keep the outside coil from freezing over long enough to produce much heat if any, I can thoroughly explain the process but it's too lengthy in short you can not get heat from cold air by using a air to air heat pump once the air temperature reaches a certain point without a backup system, a ground water source heat pump is another animal it does work at lower temperatures because the water is warm enough to keep the coils from freezing up, if you have to heat with the heat strips why waste energy cycling the unit
 
Yup, just like everyone's refrigerator/freezer can keep food at zeroF or below in a 75F kitchen or in a 95F garage.
 
$65 last month, for heating a house in Maine, is "wide open" dewy? The owners sure aren't complaining. An air source heat pump installed last fall for $3k.

Seems some modern heat pumps work well. This one is a Fujitsu Halcyon, I'm told, down to -15º F. Less efficient when you near the extreme of course. Works great in Maine this year.
 

Using the 410A refrigerant may improve cold weather performance of the heat pump . However efficiency will be reduced when used in AC mode due to very high head pressures.
The heat pump may still make heat at 0F however the wear on the pump and "efficiency" over resistance heaters do not justify the use. Energy wasted to defrost the evaporator coils increases as the ambiant air temperatures drop.
 
Unlikely in Maine they're very worried about AC. They're just thrilled with their tiny heating costs. The installer recommends oil or some other heat for extremely cold nights close to the operating extreme. So far this winter they've used less than 70 gal of oil.

You're assuming that the unit will wear prematurely? If so, that's not why they're so popular there. I'd never heard of them, installed in a friend's parents' house.
 
(reply to post at 13:26:14 02/18/15)

Most people look at home heating and cooling as the monthly oil, gas and electrical bills .
Rare does anyone calculate the overall upfront cost of HVAC equipment, service, parts, future replacement cost and energy costs all together .
 
B&D, I expect you're generally correct. Whether you are in this case I have no idea. I only know the electric bill and installed cost. Maybe the customer knows more, certainly their son is no dummy. We're acquainted through housing design, primarily my house.

I most certainly looked at total cost. Which is why I built a house that needs neither an active heating system, nor air conditioning. Virginia is decidedly an AC climate, for most houses. Tonight will be single digits, tomorrow night below 0º. We're snug, with no fear of electric outages. We can also leave for prolonged periods and have no fear that the house will ever get cold, or hot. An entirely passive system.

I was very interested to learn that my knowledge of current air source heat pumps was woefully outdated. As was clear from many of the posts in this thread.
 
Four year old 1880 sq. ft. well insulated in Middle Tennessee home. Tennessee winter low average around 24 or so . My unit is a Trane air to air heat pump with electric emergency strip built in. Most of our winter bills are $130.00 bucks or so with electric water heater and well pulling from 230 ft. Last night we broke an all time low record for this date. Went down to -4F. That is the first time I have heard the unit (does it automatic) drop off heat pump and go to strip or back up. I think they said the drop out was at 15 deg. I does defrost more when running in low temps but certainly keeps pumping warm air. Sitting on 22 out side now and discharge air is plenty warm to the feel.
 
(quoted from post at 07:29:33 02/17/15) Bryant 90+ propane furnace and matching AC.
The furnace fails to ignite quite often - it tries 4 times, and then goes to sleep for 4 hours to retry. I'm competent at cleaning the flame sensor, burners, etc. To bypass the 4 hours in really cold weather, I turn the 120v power OFF/ON to get it to restart. We're in a week of single digit temps.
an't comment on the heat pump, but I DID have a Bryant +90. You might check the igniter. I had to replace ours twice. Ours created a spark, but I believe the newer ones are hot surface. At least they're a lot cheaper than the inducer fan motor.
 
I know this is an older post, but as always I am late to the party. The OP stated his system was a 90% Bryant gas furnace with a heat pump. One main requirement with this system is the addition of a "Fossil Fuel Kit". This accessory removes the heat pump from the system any time the fossil fueled portion of the system is in operation. Installed correctly, the indoor coil will be installed in the discharge air stream of ANY fossil fueled heating plant and not in the return air stream. (If it were an electric heat system, it would be installed in the return air stream and simultaneous operation is not only ok, it is required once the structure enters the condition lower than the 'balance point' of the heat pump. The 'balance point' being the point at which the heat pump no longer has the ability to transfer heat at an efficient rate to cost ratio.)

This is why the heat pump is removed from operation.... if operating simultaneously with fossil fuel, the heat from the furnace passing though the indoor coil would drive the pressure upwards, which would be detrimental to system operation. You'd be trying to reject the heat being transferred from the low ambient temperature to the much higher temperature of the discharge air not unlike running an air conditioner and expecting it to work at roughly 140 degree outdoor air temp. 140 degrees discharge air on the fossil fuel would be a 70 degree temperature rise above the 70 degree desired room temp.

His heatpump should operate normally to the balance point, then automatically be removed as the gas takes over. The Fossil Fuel Kit should be controlled by outdoor air temperature.

At this temp, the heat pump should not be running at all because there is no way it could satisfy the given space on its own, thus being BELOW the balance point.

I would suggest conferring with a competent service organization for rectification of the issue.
 

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