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HVAC Heat Pump Question NoSpam 11-17-2008
---> Re: HVAC Heat Pump Question Nate Certified Heating and Air11-17-2008
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Posted by on November 17, 2008, 10:46 am
I have 3 new heat pump systems in my new well insulated home. Two of the
systems were working fine. The other system was had been set to 68 for
several days. This morning it was 36 outside, the actual temperature
registered on the theromastat was 68 and the aux heat was on.

My HVAC company is telling me it is normal for the aux heat to be on when
it is below 40 outside. I am questioning if that is correct or not. I
thought heat pumps worked well until the outside temperature was about 20
degrees.

Is my HVAC company correct? If not, at what outside temp should the aux
heat be necessary in a well designed properly working system? Can you
provide any reasonably authoritive info on the web that I can show to them?

Many thanks for any help.

Posted by on November 17, 2008, 11:23 am
On Mon, 17 Nov 2008 10:46:47 -0500, NoSpam@aol.com wrote:

>I have 3 new heat pump systems in my new well insulated home. Two of the
>systems were working fine. The other system was had been set to 68 for
>several days. This morning it was 36 outside, the actual temperature
>registered on the theromastat was 68 and the aux heat was on.
>
>My HVAC company is telling me it is normal for the aux heat to be on when
>it is below 40 outside. I am questioning if that is correct or not. I
>thought heat pumps worked well until the outside temperature was about 20
>degrees.
>
>Is my HVAC company correct? If not, at what outside temp should the aux
>heat be necessary in a well designed properly working system? Can you
>provide any reasonably authoritive info on the web that I can show to them?
>
>Many thanks for any help.


There are a couple of instances when heat strips come on;

1. When the unit goes into defrost mode.

2. When the user adjusts the thermostat to be 3 to 5 degrees (depends
on the stat) greater than the indoor temperature that is indicated on
the thermostat.

3. When there is a outdoor thermostat (connected to the outdoor unit)
that senses when the outdoor temp goes below a preset temperature.

4. When the thermostat is miswired.

5. When the defrost control board malfunctions.

I suspect that your installers are right and that the unit in question
has an outdoor thermostat and is doing what it is supposed to do as no
heat pump will heat efficiently at 20 degrees outside air temp, most
start loosing efficiency at around 35 degrees. I would want to know
why the other two are not doing the same thing.

Posted by on November 18, 2008, 10:01 pm


On Mon, 17 Nov 2008 08:23:18 -0800, Nate Certified Heating and Air
Professional wrote:

>On Mon, 17 Nov 2008 10:46:47 -0500, NoSpam@aol.com wrote:
>
>>I have 3 new heat pump systems in my new well insulated home. Two of the
>>systems were working fine. The other system was had been set to 68 for
>>several days. This morning it was 36 outside, the actual temperature
>>registered on the theromastat was 68 and the aux heat was on.
>>
>>My HVAC company is telling me it is normal for the aux heat to be on when
>>it is below 40 outside. I am questioning if that is correct or not. I
>>thought heat pumps worked well until the outside temperature was about 20
>>degrees.
>>
>>Is my HVAC company correct? If not, at what outside temp should the aux
>>heat be necessary in a well designed properly working system? Can you
>>provide any reasonably authoritive info on the web that I can show to them?
>>
>>Many thanks for any help.
>
>
>There are a couple of instances when heat strips come on;
>
>1. When the unit goes into defrost mode.
>
>2. When the user adjusts the thermostat to be 3 to 5 degrees (depends
>on the stat) greater than the indoor temperature that is indicated on
>the thermostat.
>
>3. When there is a outdoor thermostat (connected to the outdoor unit)
>that senses when the outdoor temp goes below a preset temperature.
>
>4. When the thermostat is miswired.
>
>5. When the defrost control board malfunctions.
>
>I suspect that your installers are right and that the unit in question
>has an outdoor thermostat and is doing what it is supposed to do as no
>heat pump will heat efficiently at 20 degrees outside air temp, most
>start loosing efficiency at around 35 degrees. I would want to know
>why the other two are not doing the same thing.

The units do not have an external thermostat. In case it helps, the units
are American Standard. The thermostats are "ACONT800 Series Touch Screen
Programmable Comfort Control" units.

Posted by sanity on November 17, 2008, 3:44 pm

>I have 3 new heat pump systems in my new well insulated home. Two of the
> systems were working fine. The other system was had been set to 68 for
> several days. This morning it was 36 outside, the actual temperature
> registered on the theromastat was 68 and the aux heat was on.
>
> My HVAC company is telling me it is normal for the aux heat to be on when
> it is below 40 outside. I am questioning if that is correct or not. I
> thought heat pumps worked well until the outside temperature was about 20
> degrees.
>
> Is my HVAC company correct? If not, at what outside temp should the aux
> heat be necessary in a well designed properly working system? Can you
> provide any reasonably authoritive info on the web that I can show to
> them?
>
> Many thanks for any help.

When I purchased my house 3 years ago, the heat pump was set at 30 degrees.
Below 30 the auxiliary gas furnace would come on then.
I found the heat coming from the pump insufficient to heat the house
properly at 30 and my electric bills were soaring.
The following winter I had them set the pump to 35 with almost the same
results as the first year. I called the company and they told me that they
recommend the heat pump to cut off at 40 degrees outside temp and have the
auxiliary come on then.
So far, my house is warmier and cozier. I can't tell what the bills will be
like but I assume my electric will go down and my gas up but I don't really
care as the house is now comfortable. When the gas heat comes on, it comes
on with more intensity that the heat pump, heats the house rapidly and shuts
down
whereas my heat pump used to run almost continuously.
Hope this helps.



Posted by Kenneth on November 17, 2008, 9:21 pm
On Mon, 17 Nov 2008 10:46:47 -0500, NoSpam@aol.com wrote:

>My HVAC company is telling me it is normal for the aux heat to be on when
>it is below 40 outside. I am questioning if that is correct or not. I
>thought heat pumps worked well until the outside temperature was about 20
>degrees.

Howdy,

We live in New Hampshire and occasionally have had days as
cold at -20F.

We heat with water to air heat pumps with no auxiliary heat.

It all depends on the capacity of the system as designed.

All the best,
--
Kenneth

If you email... Please remove the "SPAMLESS."

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