Heat pump operation

Home has a 2 ton Carrier air source heat pump. 17 years old

Temperature at time of the inspection was 15 degrees. It was operating in the heat mode and heating properly.

I do not get how it was extracting heat from the outside air at 15 degrees.

Mine is set at 30 degrees and it is a 2008 unit.

I do not understand how the exterior unit can take 15 degree air and operate properly.

I also tried in emergency heat mode and it operated.

What do you mean by “mine is set to 30 degrees” ?

Is that when it switches over to an aux heat source?

Heat pump operation depends on the type of refrigerant, the newer R410 is much better since it is used in units that have other advanced designs.

At 15 deg F, some heat can be absorbed from the exterior but most likely it was running in regular and aux heat strip mode at the same time if you had good warm air. If you had the t-stat up over 2 degrees it would have been running the electric strips also unless programmed out via a special t-stat that also uses an exterior temp sensor. Some units can even sense that the house is not gaining any heat and will add in the aux strips even at a one degree t-stat command.

Yes, my unit switches over to gas.

The thermostat at this home indicated it was running in normal heat mode. The heat pump was running when I arrived and I tried turning up 10 degrees to see if the aux heat would automatically turn on. It did not.