Whenever the temperature is above freezing temperatures the system can easily use electricity to generate heat (or air, if it's reversible). This type of heat isn't as warm, but still distributes comfortable heat evenly throughout the living quarters. However, when the air gets extremely cold and below freezing temperatures, the pump starts to switch (automatically in most cases) to supplemental gas power. This makes the system not only affordable but also warmer.

There are definite disadvantages to gas power and electrical power in their own right; when combined the two systems complement each other, giving one the "best of both worlds." The only potential disadvantage here is the startup cost, much like geothermal pumps. Dual-fuel pumps run upwards of $1,000 sometimes because you are basically buying two systems-in-one.

Company Resource: Ground Source Heat Pump, Water Source Heat Pump, Waste Water Source Heat Pump