While heat pumps are one of the most efficient sources of heat in temperatures above ?37°F. Below that temperature, there just aren’t enough BTUs in the ambient air to derive enough heat for your home. In fact, heat pumps provide warm air ? 15° – 20° F above the air temperature in the room (at the registers). Often times, a heat pump cannot replace heated air as quickly as it is lost through seals of windows and doors. For this reason, there is an “Emergency Heat” option on homes that depend primarily on heat pumps for their home’s warmth. Although heat pumps are becoming more and more efficient, there are still those times when the secondary stage must be used to provide enough warm air for your home.
How a Heat Pump Provides Heat in Winter
Essentially, a heat pump moves warm air to colder areas. Basic physics dictates that warm air will seek a cooler space to migrate; the heat pump harnesses this warm air and transfers it into your home. Think about how your refrigerator removes warm air (when door is opened or leftovers are placed in) from inside, transferring it outside via the fan. Most residential heat pumps are air-to-air; transferring warmer air to cooler spaces. (In summer, the unit transfers hot air from inside your home to outside).
When the temperature drops below ? 37°F, an auxiliary heat source must help to heat the air in your home. When the thermostat is set more than 1°F above room temperature, the emergency heat will kick in. As an assistant to the heat pump, the second stage heating within an all-electric heat pump is most commonly a set of electric resistance heaters on the inside unit. Though the cost to warm your home with this auxiliary electric heat can be terribly expensive, there are alternatives to keeping the second stage from operating.
Alternative “Emergency Heat”
Because the all electric air-air heat pump emergency heat can be so expensive, there are alternative sources:
1. Geothermal Heat Pump – using the consistent ground (geo) heat (thermal) of ? 56°F, there is enough heat to transfer to your home all winter. While the initial installation and material cost may be higher than an air-air heat pump, the operating cost savings will pay for the unit in just a few winters.
2. Gas Fired Furnace – installing a gas fired auxiliary furnace to operate in extremely cold conditions will provide your home with warm air regardless of the outside temperature. Depending on your heat pump set-up, this option must be designed as a system adjunct to your Bellevue Heat Pump.
3. Oil Fired Furnace – similar to the gas fired option, the oil fired furnace must be designed into the heat pump’s system as the emergency heat supply.
Remember, a heat pump’s auxiliary heat will kick in when the thermostat is calling for a temperature increase that is more than 2° higher than the room temperature. By keeping the thermostat within that set point, the emergency heat will not be activated. If your family cannot tolerate the cool (albeit warmer) air provided by a heat pump, perhaps using the heat pump in summer and an auxiliary heating system in winter is the option that best suits your need.