Heat Pump Not Heating After a Power Outage?
The EM Heat setting on a heat pump’s thermostat stands for emergency heat.
October 26, 2022

It’s cold outside, but you’re nice and toasty inside thanks to your energy efficient heat pump – then the power goes out. Of course, the heat pump is no longer running, but will it start right back up when the power is restored?

The answer is yes, but it might not be able deliver heat right away, like a gas or electric furnace would. It depends on how cold it is outside and how long the power is out.

If the outage is brief (less than a half-hour) and the outdoor temperature is in the high 30s or above, your heat pump should begin heating your home as soon as the power comes back on. But if the power outage is longer and the outdoor temperature is colder than 35 °F, the refrigerant might be too cold to flow freely. In this case, the refrigerant will need to be warmed up before your heat pump can resume heating your home.

That’s where emergency heat comes in.

Understanding the Functions of the Emergency Heat Setting

The emergency setting, usually abbreviated EM on the thermostat, is designed into a heat pump for two main reasons.

One is to activate your backup heating system when temperatures are too cold for a heat pump to operate efficiently. At temperatures approaching or below freezing, it is more energy efficient for a gas- or electricity-powered backup system to heat your home. Once the outdoor temperature warms up, the heat pump will take over again.

The other function of emergency heat comes into play when the refrigerant is too cold to flow. In this case, the emergency heat setting enables the heat pump’s compressor to bring the refrigerant back up to operating temperature. And once that temperature is reached, your heat pump will resume keeping your Atlanta home warm and comfortable.

Manual vs. Automatic EM

If you ever face the situation where the refrigerant is too cold after an outage, it’s helpful to know beforehand how to activate the emergency heat. With an older heat pump, it is likely that you’ll need to manually set the thermostat to EM. In newer models, the emergency heat will usually start automatically. These are, of course, general guidelines, and we recommend you consult the owner’s manual for your specific model.

Questions about installing or operating a heat pump in your Atlanta home? Ask the HVAC experts at Comfort Zone. We provide homeowners in Atlanta and surrounding areas with knowledgeable service, economical heating and cooling options, and guidance you can trust.

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