What temperature is too cold for a heat pump to work?
Friday, January 3, 2020
When the outdoor temperature heads below 32º F (freezing) a heat pump won’t work well and becomes more inefficient the colder it gets. You have to understand how a heat pump functions to know why this happens. It does not generate heat. Instead, a heat pump absorbs heat in one location and moves it to another.
The system absorbs indoor heat in the summer and exhausts it outside, then reverses itself to move outdoor heat indoors during the winter. As the temperature moves below freezing, there is less heat to grab and the system has to work much harder to pull out any heat.
Luckily, heat pump systems also have a supplemental (backup) heat source to turn to when it gets really cold, usually an electric resistance heat coil— or sometimes a gas furnace. The system will sense when it needs to switch to the alternate heat source and do it automatically. It is not necessary or recommended to turn the thermostat setting to “EM HEAT” (emergency heat) on very cold days.
This issue does not apply to ground source (geothermal) systems. There are not too many of them out there, but they use underground piping to tap into the relatively constant temperature of the soil a few feet below grade. Most systems are “air source heat pumps."
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To learn more about heating and air conditioning systems, see these other blog posts:
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