Heat pumps heat and cool by moving heat from one place to another. In heating mode, heat pumps are essentially an air conditioner running in reverse. Latent heat energy in exterior winter air is pulled by refrigerant circulating through the outside coil. The heat is concentrated since the refrigerant passes through the compressor and then conveyed inside to a coil set up in the indoor air handler. Since the refrigerant rapidly depressurizes in the coil, it discharges its load of concentrated heat energy. That heat is spread through your ductwork by the blower and efficiently warms your house — except when it doesn’t.
The Balance Point
Many people are surprised to learn that there’s sufficient heat in cold winter air to warm a house. But it’s true just to a point. Depending on the efficacy of this unit, there’s a particular outdoor temperature — known as the balance point — in which the heat pump may no longer extract enough heat energy to get the job finished. For many residential heat pumps today, that is somewhere about 35 degrees Fahrenheit. Below that amount, most units incorporate electric resistance coils mounted in the air handler that automatically energize to supply the supplemental heat required to keep the house toasty.
An Electric Drawback
So what is the downside of a heat pump when weather turns really cold? Electric supplemental heating required below 35 degrees is substantially more expensive than either heat in a heat pump or gas-fired heating. If exterior temperatures often drop below the minimum, homeowners may discover that savings gained by using the efficient heat pump are negated by the high operating costs of regular reliance on supplemental electric heat.
Dual Is much better Than One
A dual-fuel furnace requires on the issue with a hybrid approach that combines a heat pump and a backup gas-fired heater. So long as exterior temperatures stay above the balance point, the heat pump manages the job of keeping the house warm with typical heat pump energy-efficiency and very low operating costs. Meanwhile, an outside sensor and thermostat constantly monitor the outside air temperature. If it falls into the balance point, then the thermostat controller automatically shuts down the heat pump and also actuates the copy furnace. When exterior temps again rise above the balance point, the gas-fired unit closes down and the heat pump kicks again. Since natural gas is significantly less expensive than power, the family heating budget requires a considerably smaller hit when the system utilizes the gasoline backup furnace.
More Great News
Many installed gas-fired furnaces can be configured as the backup heater in a dual-fuel arrangement. It isn’t always required to buy a new, separate furnace. Thus, a homeowner with an current split central air conditioner/furnace system may choose to upgrade just the A/C to a high-efficiency heat pump which delivers both cooling and heat, while retaining the installed gas furnace to present cost-effective supplemental heat whenever low temperatures demand. An HVAC contractor can readily install the outside sensors and thermostat controller necessary to join and actuate the respective units.