With the first frosts of winter come the first phone calls from customers asking when they should switch their heat pump thermostats to e-heat. The short and quick answer: "Usually, never."
A properly designed and installed heat pump can operate continuously in cold weather. E- heat, which stands for emergency heat, should only be used in a real emergency, like when your heat pump fails.
How a heat pump works
In heat mode, your heat pump is like an air conditioner working in reverse to pull heat from the outside into your home (yes, there is "heat" in the "cold"). The electric strip heat from your furnace -- it shows up as "e" or "em" or "aux" on your thermostat -- comes on automatically to help heat your home.
Points well taken
Energy consultant Greg Jourdan says there is no point where it's necessary to switch to emergency heat, even if your heat pump is running constantly due to cold weather.
Jourdan, professor of Environmental Systems and Refrigeration Technology at Wenatchee Valley College, explains that your heat pump has a balance point where it may not be able to extract enough heat from the outside air during cold spells. This is typically around 20 degrees F. When the temperature outside gets below the designed balance point and the temperature in the home starts to drop, the second stage of your auxiliary heat (your furnace heat) will automatically switch on. The furnace supplements the heat pump to maintain the set point at your thermostat. It will automatically control and compensate during cold conditions to keep your home comfortable.
Switching can cost you
Heat pumps are much more efficient than furnace/auxiliary heat. Switching manually to the e-heat setting on your thermostat can ramp up your electric bills needlessly.
Bottom line: Use emergency heat only if your heat pump isn't heating your home at all. In that case, call an HVAC professional.
>Read Greg Jourdan's Simple Energy-Saving Tips