What is the balance point of a heat pump?

The balance point is the outdoor temperature at which the heat pump's declining capacity exactly equals the building's rising heat loss. Above it the pump alone keeps the house warm; below it supplemental backup heat must make up the shortfall.

How is the balance point calculated?

Capacity is drawn as a line through two manufacturer data points and heat loss is drawn as a line proportional to the indoor-minus-outdoor temperature difference. The balance point is where the two lines intersect, solved algebraically.

Why does heat pump capacity fall as it gets colder?

As outdoor air cools there is less heat available for the outdoor coil to absorb, so the compressor moves less heat indoors. Capacity drops roughly linearly with outdoor temperature, which is why two table points define the capacity line well.

What is a good balance point temperature?

A balance point around 30 to 35 degrees F is typical for a correctly sized cold-climate system. A very high balance point means the pump is undersized and backup heat runs often, raising running costs; a very low one suggests oversizing.

What is the UA value the tool reports?

UA is the building's heat loss coefficient in BTU per hour per degree F. It equals the design heat loss divided by the design temperature difference and lets the tool compute heat loss at any outdoor temperature.

Heat Pump Balance Point Calculator

A heat pump loses capacity as the outdoor air gets colder, while the building it serves needs more heat at the same time. The balance point is the single outdoor temperature where those two curves cross. Knowing it tells you when backup heat must stage on and lets you size supplemental heat and set thermostat lockouts correctly.

How it works

Two lines are drawn and intersected:

capacity(T) = cap2 + slope * (T - temp2)      slope = (cap1 - cap2)/(temp1 - temp2)
UA          = design_loss / (indoor - design_outdoor)
heat_loss(T)= UA * (indoor - T)

The balance point is the outdoor temperature T where capacity(T) = heat_loss(T). Setting the two expressions equal and solving for T gives:

T = (UA*indoor - cap2 + slope*temp2) / (slope + UA)

Capacity rises with outdoor temperature while heat loss falls, so the lines cross once, at the balance point.

Example and tips

A unit rated 36,000 BTU/h at 47 °F and 24,000 BTU/h at 17 °F, serving a home with a 30,000 BTU/h design loss at 5 °F outdoor and 70 °F indoor, balances at roughly 27 °F. Always use the heating capacity table, not the cooling tonnage, and pick two points that bracket your climate. Set the auxiliary-heat lockout a few degrees below the balance point so the pump is given the chance to carry the load before resistance heat is allowed in.