The specific temperature at which an air-source heat pump becomes inefficient and it is more cost-effective to switch to a natural gas backup system can vary depending on several factors, including the efficiency of the heat pump, the cost of electricity and natural gas in your area, and the insulation and size of your home.
Air-source heat pumps are generally efficient for heating, even in cold climates. However, as the outdoor temperature drops, the heat pump's efficiency decreases. This is because the heat pump needs to work harder to extract heat from the colder outdoor air to heat your home.
Most modern air-source heat pumps can efficiently heat a home in temperatures as low as 20 to 25 degrees Fahrenheit (-6 to -4 degrees Celsius). Beyond that point, the heat pump's efficiency may decline, and it may require more energy to maintain desired indoor temperatures. As a result, the cost of electricity for heating can become less favorable compared to using a natural gas backup system.
In areas with colder climates where winter temperatures regularly fall below the heat pump's optimal operating range, homeowners often have a backup heating system, such as a natural gas furnace or boiler. The backup system kicks in when the heat pump's efficiency drops significantly, providing efficient heating at lower temperatures.
To determine the specific temperature at which it becomes more cost-effective to switch from your heat pump to a natural gas backup system, it is recommended to consult with a heating professional or energy expert. They can assess your specific circumstances, energy costs, and conduct a cost analysis to help you make an informed decision.