STS-134
Active Member
Heat pumps cannot add moisture to the indoor air but they certainly can remove it. When operating in AC (when it is a desired and likely part of operation when the air is moist) or defrost mode, moisture can condense on the indoor coil (in practice this is very unlikely to happen in defrost mode because the heat pump has been heating the air, decreasing the relative humidity level, while the absolute humidity, i.e. the dew point, remains unchanged), and you'd need to cool the air below its dew point, which is generally the temperature of the outside air or lower, in order for condensate to form. If you are using a gas furnace as your auxiliary heat, this would never happen, because the furnace heat exchanger comes before the indoor coil and the air would first be heated and then cooled; it is possible but highly unlikely when using heat strips, which come after the indoor coil.As @STS-134 it doesn't directly add or remove moisture
Of course, heat pumps can and do remove moisture from the outdoor air when they're in heating mode as they cool the outdoor air below its dew point and condensate forms on the outdoor coil. If the outdoor coil goes below freezing, the condensate will form as ice, which is the entire reason heat pumps need a defrost mode in the first place.
That's more dependent on your thermostat than your heat pump. Most modern thermostats will let you adjust the temperature swing.however to the extend that narrower band of temperature helps with air quality then it will help. The main thing with a heat pump is your not going to be swinging the temperature as much. The output temp is lower (which is better in my opinion).