Auxiliary heat is generally electric strip heaters. In some instances a gas furnace is used in an application called “Dual-Fuel Heat Pump.”
Heat pump heat is more gentle than that of a forced air gas furnace. The indoor air discharge temperature of a heat pump is much cooler than that of a gas furnace. The air from a heat pump is not subjected to the extreme heat of the gas flame and therefore is not baked and dried out. Due to this gentle heating of the air heat pumps usually have little need of a humidifier to improve personal comfort.
The discharge air of a heat pump (the air coming out of the register) is relatively warmer than the room temperature, thus heating occurs. The discharge air is cooler than the body’s temperature and subsequently any air blowing directly on you may feel cool or drafty.
Heat pumps will loose effectives (but not heating capability) as the outside temperature get progressively colder. As the outside temperatures cool the defrost cycles will happen more often, last longer and the amount of heat available outside will reduce. As the outside temperature drops the heat loss of the structure will increase.
There are two arguments concerning the turning off of a heat pump when the temperature drops below a given point. My suggestion is to leave the unit running, and here is why.
Note 1: This is not applicable if you are operating a dual-fuel system.
Note 2: These arguments are only valid for a system that is in good operating condition.
1) Winter precipitation will not stick to the fan blade if it is running and moving air or if the unit is in defrost mode.
a) When a unit restarts and ice has frozen to the blade it will either be terribly out of balance and shake itself to death or will be seized by the ice and burn the motor out.
b) If there is power outage during freezing precipitation DO turn off the unit and Do Not turn it back on until you have inspected the fan for the absence of ice.
2) The reduced heat production caused by low outside temperatures is most often cheaper than electric heat.
3) The unit will automatically bring on the supplemental heat when the thermostat recognizes a drop in inside temperature. Usually about 2 degrees below setpoint. If you find this uncomfortable, raise the setpoint 2 deg.)
The only time I recommend turning off your heat pump is when it is not operating properly. Not operating properly will of course include those times when the power is out.