What part of the country are you in? Do you know the size of the outdoor unit? It worked well in summer?
3100 SF with 25 foot ceilings and open loft and not well insulated probably requires over 5-tons. The largest units are only 5 tons

Does auxiliary heat ever seem to appear on the thermostat? Its possible your undersized and its working nonstop to maintain which is unusual for this type of mild weather.

You can invest in a thermometer and you could measure the temperature at the registers.

What temp did you keep the house in the summer when it was hot? Did it maintain it?

At 50F, my HP will put out over 100F air. At 35F it's around 85F.

Now that it is cold enough for the HP to actually make heat, it would be good to have it checked again.

neohioheatpump - We're in Indiana. Hubby says unit is 5-ton.

The last owners had ridiculously high electric bills, even in summer, but they didn't follow simple energy-saving procedures (i.e., they let the sun stream in all day, didn't close off unused rooms, etc.). We were careful to make the place as efficient as possible and were delighted with the $100-$125 summer bills; we were quite comfortable with the thermostat between 71 and 75 (although the loft was warm until after sundown, which didn't bother us). Sometimes the A/C didn't come on until mid-afternoon (we have plenty of tree shade) and the blower did NOT continue on and on unless I turned the fan to "on."

The auxiliary heat switch on the thermostat is not lighting up -- I've looked often, LOL, fearing it. Aux heat on previous homes in this zone rarely cut on - and, as you wrote, definitely not with just 35-60 temps. Your advice to take the temp at the registers makes sense and I will do that. Sure hope a second unit won't be necessary. Thank you.

weedmeister - Thanks. Yes, it does sound like another check is in order for us.

In the meantime, the main level bathroom is roasty toasty, so I may be moving my laptop and tea in there!

Get the unit checked pronto.

It is working way to hard and it is not even that cold yet.

A May check could not have set the unit up for heating operation very accurately.

Thanks, brickeyee. Calling for service tomorrow.

could be a bad thermostat

Get the unit checked. Let us know what the problem was. I'm definitely curious. Thats weird if it works for cooling but not heating. How efficient is this unit? If its between 5 and 10 years old is should hopefully be atleast 12 seer which isn't bad.

juliekcmo: Yes, it could be the control at the thermostat or the control wiring -- which sounds so much better as a repair than needing a new air handler.

neohioheatpump: I don't know the SEER (WISH it were 15!) but will check. Yes, I'm stumped as to why it functioned so well over summer, but now...

Service tech is coming out this afternoon, and I will definitely report back. I'm always curious as to the outcomes of folks' postings and delighted when someone actually concludes the posting with the end result.

Thanks, all.

So, the service guy came and checked out the unit. Problem 1: Faulty high limit switch. Since this is a safety issue, I'm pleased to have that replaced. Problem 2: The unit, as neohioheatpump suggested, is not quite big enough to keep the place roasty toasty (with the exception of that still-majorly-needs-a-makeover bathroom); hence, the fan keeps going and going and going like the Energizer bunny, trying to maintain a reasonable temp.

We are mulling over the feasibility of a new heat pump and possibly a new air handler, but because we still have 14 more rooms and all the outside left to re-do, we were hoping it could wait a bit. However, there is a tax credit of up to $1500 which could take away some of the monetary sting if we go for it by 12/31.

If we don't bite in the next few weeks, we'll probably perform as many non-costly energy-saving upgrades before winter hits; take advantage of Mr. Ceramic Heater and Ms. Heated Mattress Cover; see how the heat pump functions through the next few months; weigh the comfort (or should I say, discomfort) level - and then proceed accordingly.

If you hear screaming, it just might be me, opening the electric bill.

Thanks again to my GW friends.

with the limit switch corrected is it doing a better job? What is a limit switch?

I would still think your 5-ton unit could handle this type of weather no problem even if its a bit undersized. 5-tons is the largest size available. You would have to get a larger unit to add size.

Sorry for the delay...

My hubby was so very incorrect about the unit being 5-ton. It's a mere 3-ton. We are thinking of moving up to a 4-ton and would also need to buy a new air handler.

The high limit switch was replaced. My rudimentary understanding is that it protects the furnace from over-heating by making the furnace shut down periodically, so that a problem (such as a bad filter inhibiting air flow) doesn't cause the furnace to cycle constantly, in which case it would eventually burn itself out. It's located within the upper body of the furnace.

Apparently, the switch, being faulty, did not shut down the furnace, thereby allowing the cycle to go on and on. And yes, it now works better, cycling on and off. However, it still runs more than I'd like and I'm anticipating some doozey heating bills (if we don't break over and purchase a new heat pump soon).

Thanks again.

3 tons might be the correct size. When you say 3100SF - do you mean 1500 sq. foot ranch with 1500 sq. foot basement?

How cold is it where your at? Currently its been getting into the mid 30's at night. My heatpump probably runs about 20 minutes per hour in the mid 30's outside temps.

If the heatpump is running properly, and your house isn't super leaky it shouldn't be running non-stop. In this type of weather. This weather isn't extreme.