This graph shows the balance point for a very efficient, state-of-the-art Air to Water CCHP. This example also assumes a tight, well-insulated conventionally-constructed building envelope. In this example you would begin to need supplemental heat at around 15º.

The two variables of heat pump heating capacity—the red line in the graph, and building heat loss*—the blue line in the graph.  This will determine the temperature at which your particular heat pump can no longer keep up with the demand for heat.

* (as measured by a heat loss calculation )

Auxiliary heat

Some heat pumps have built-in auxiliary heat. At the point that the heat pump can not keep up with the heat loss it will turn on the backup electric, resistance heater. Resistance heat is two to four times less efficient than the heat pump’s typical performance. This can lead to high electric bills during the coldest part of the winter. Consider these other forms of auxiliary heat:

Direct-Vent Gas Heaters

Direct-vent gas heaters have the advantage of combusting the fuel right in the room where heat is needed, instead of ...

Electric Baseboard

Even though electric baseboard heaters work on resistance heat which does not have the leveraging effect of a heat pump, ...

Wood Stove

A wood stove works great in a home with an open floor plan. In addition to the ambience and comfort ...

Wood Pellet Stove

A wood pellet stove has a few advantages over traditional wood stoves: A wood pellet stove doesn't need to be ...

Fireplace Inserts

A fire in your fireplace gives the room a comforting glow and does warm a small area. The EPA estimates ...

Fireplace

The warmth of an open fire resonates deeply in our species, but 90% of the fire heat goes up the ...

Miscellaneous Electric Heaters

There are a variety of electric resistance heat emitters on the market. Wall and ceiling mounted units are typically found ...

For a more complete discussion of heat pump performance in different kinds of buildings see How Cold is too Cold for a Cold Climate Heat Pump?