HVAC Heat Pump Question

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.
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On Mon, 17 Nov 2008 10:46:47 -0500, snipped-for-privacy@aol.com wrote:

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

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.
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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.
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On Mon, 17 Nov 2008 10:46:47 -0500, snipped-for-privacy@aol.com wrote:

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

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I'd say it's not the capacity that's the factor in this case, but that your system is water based and by all indications, the poster's is the more common air based.
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On Tue, 18 Nov 2008 09:20:32 -0800 (PST), snipped-for-privacy@optonline.net wrote:

Hmmm, of course you may be right...
All the best,
--
Kenneth

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snipped-for-privacy@aol.com wrote:

I'd say that, unless there is a failure, your system is undersized.
I'd be unhappy if resistive heaters came on before the outside temperature dropped to within 15 or so Fahrenheit degrees above the design low temperature (lowest minimum temperature) for your area.
The only exception would be if the house's heating had been turned way down, as if you were away on a winter vacation, and upon return you were trying to rapidly raise the interior temperature rapidly.
Boden
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