Heat Pumps are not designed to keep your house warm when its bitter cold outside. They are designed for a moderate climate, which we usually have. When the temperature goes into the single digits and stays there a while, your heat pump can’t do the job. As the temperature starts to fall in the house, usually 2 degrees below setpoint, the backup strip heat should kick in to help. If it still can’t keep your home tolerable, there may be something wrong. Foothills Mechanical can help. Call us at 856-0030.