For year-round heating and cooling comfort, heat pumps work great in areas of the country with moderate temperatures. This is especially critical during the heating season. Once the outdoor temperature goes below 25° - 30° F, a heat pump can continue to provide heat. However, it will use more electricity to do so, which means higher utility bills. This is because there simply isn’t as much heating energy available as the outdoor temperature drops and the system will work longer to achieve the same indoor temperature. That’s why many air-source heat pump systems are installed with a supplemental heat source.
Source https://www.carrier.com/residential/en/us/products/heat-pump...
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