Heat pumps can effectively heat homes and buildings even in cold climates, although their efficiency does decrease as the temperature drops. Modern heat pumps can operate in temperatures as low as -13°F (-25°C), thanks to advancements in refrigerant technology and system design. However, in extremely cold climates, a supplemental heat source, such as an electric resistance heater or a gas furnace, may be necessary to maintain comfortable indoor temperatures. Dual-fuel or hybrid heat pump systems, combining a heat pump with a furnace, offer the optimal balance of efficiency and comfort in cold climates.