How does a heat pump heat when it is cold outside?
A heat pump moves heat from outdoor air into the house using refrigerant, and even cold air contains some heat. As the outdoor air gets colder there is less heat to move, so the unit works harder and delivers less warmth per hour of running.
This is the reverse of how an air conditioner works, and the same outdoor unit does both jobs. A reversing valve switches the direction of refrigerant flow when you change modes.
Cold climate heat pumps are built with improved compressors and controls to keep going at lower temperatures than standard models. Which type you have matters more than the number on a chart.
Efficiency is measured by how much heat the unit moves compared with the electricity it uses, and that ratio falls as the outdoor air cools. Installed correctly, with clean coils and good airflow, a heat pump stays efficient across most of what a Phoenix area winter delivers.
What is auxiliary heat and emergency heat?
Auxiliary heat is a backup, usually electric heat strips in the air handler, that turns on automatically when the heat pump cannot keep up. Emergency heat is a manual setting that runs the backup alone, intended for when the heat pump itself has failed.
Backup heat costs more to run than normal heat pump operation, so frequent use is a clue that something is wrong. In the West Valley, backup heat should run only occasionally during short cold snaps.
If the thermostat shows AUX or EM HEAT often during mild weather, have the system checked. Low airflow, a refrigerant problem or a failing outdoor unit can force the backup to carry the load.
Heat strips glow like a toaster and warm the air passing over them, so the air from vents may feel hotter than normal heat pump air. That is normal. What is not normal is a thermostat showing backup heat all day while the outdoor unit sits idle.
Why is a heat pump blowing cool air in winter?
A heat pump blowing cool air may be in a defrost cycle, which briefly reverses the system to melt frost on the outdoor coil. It can also mean a dirty filter, low airflow, a refrigerant leak, or a failing reversing valve, which are worth having diagnosed.
Defrost is normal. You may see steam rise from the outdoor unit and the indoor air may feel cooler for a few minutes. If the cool air lasts and the house keeps dropping in temperature, something else is going on.
Start with the simple checks. Make sure the filter is clean, the registers are open, and the thermostat is set to heat, not cool or fan only.
A technician checks the outdoor coil, the reversing valve, refrigerant pressures and the defrost controls. Heat pumps rely on proper refrigerant charge, so a leak shows up as weak heating as well as weak cooling. Fixing the leak and the charge restores output.
Do West Valley winters stop heat pumps?
West Valley winters rarely get cold enough to stop a properly working heat pump, so backup heat should run only occasionally. If your system struggles during a cold snap, the cause is more likely a fault, restricted airflow or poor defrost than the weather.
Homes in Sun City, Sun City West and Surprise often use heat pumps for both cooling and heating, so the equipment works hard all year. Maintenance before winter helps catch problems early.
Vortech repairs heat pump systems across the West Valley. If your home will not warm up, turn the thermostat to heat, check the filter, and use the call button on this page.
Because the same equipment cools in summer, one failing part affects both seasons. If the system has struggled since last summer, winter often exposes the problem. Having it looked at in the fall is easier than waiting until a cold morning.
More questions: Heat Pumps in Arizona: 12 Questions Homeowners Ask