Heat Pump Question

[oil pan 4]

I have a question about heat pump operation. I know the principles behind them and such, and even did light maintenance on mine a few times over the years. But one thing has me a bit stumped: My heat never seems to get up to the correct temp. The system was replaced in 2019 from a 2005 build. Right now it's 29*F outside. My thermo is set for 72.*F. My heat pump will only get to 67-68 max. If I go to the Thermostat and turn to EMER heat, it will come on up. This, obviously is not a good way of keeping the bill low, As it shuts down the outside unit and uses only the electric strips. But from what I've been able to gather, in conditions like this, there is supposed to be an 'AUX HEAT" indication that comes on that allows the strips to come on, while the outside unit runs as well, and thus, allows the heat pump to catch up to the thermostat setting. The thing is, I never see such an indication, nor is there a setting for it (other than "OFF", "COOL", "HEAT", EMER") on my thermostat. Does my unit just not have such a setting? If I turn on the EMER heat, it will bring up the temp within 20 minutes, then usually stays there for the most part. but once the outside temp drops again, the cycle starts all over. Could this be the thermostat itself (It was the previous units, and is one of those programmable ones, but I only use the hold setting on it)? TEH last time I had the installer look at it, last summer, everything was good.

Yep mine does the same thing. That's why I leave the heatpump on the lowest setting and use my wood stove.

 

[KrisZ]

It’s likely a thermostat wiring issue. The Aux heat should be coming one automatically. Since it comes on manually, wiring is likely the cause. Your HVAC guys is an amateur, I would ditch him.

 

[Propflux01]

Digital thermostats are usually programmable for how many degrees the temperature has to drop below the setpoint before aux heat is activated. Get the manual for your thermostat and check the programming. A good setting if you don't change the setting much would be 2 degrees. If you do fall back the temperature at night you'd want to have it wider to avoid running electric heat to warm up in the morning.

The fact that "Emergency" works should mean that the wiring is correct-- its the same wiring (the white wire) and heat strips used for Aux.

It’s a 3 ton unit. I got into the thermostat and programmed the three stages to 1.5*f separation on the compressor stage, and 2.0 on the strips, and noticed an immediate change in how it heats. So far it’s been keeping it heated, although I still don’t see “aux heat” ever show up when running, as long as it’s not blowing out the cold air anymore and not running constantly I’m happy. We will see how the electric bill goes before I change anything else.

 

[ironman_gq]

Doesn't sound right, I've got an 18kbtu unit and it'll keep a 1000SF space at 68F down into the single digits without using any auxilary heat strips. Head unit doesn't have them, there is an element in the ground unit to help with defrost but it rarely comes on.

 

[Fitter30]

15 kw is 51,150 btu's Heat pumps are sized at 47° outside temp. All heat pumps as the outside temp drops so does their capacity and below 17° the capacity fall faster unless it a hyper heat design and can operate down to -13° still loses some capacity but not near a standard hp.