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.

What is the Heat Pump Balance Point Calculator?

Plots heat pump heating capacity from manufacturer table data against the building heat loss line to find the balance point where backup heat must stage on. Helps HVAC designers size supplemental heat and set thermostat staging. Runs in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Heat Pump Balance Point Calculator

Name: Heat Pump Balance Point Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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.

How to read the balance point for system design

The balance point is the threshold that separates two operating regimes:

Above the balance point: The heat pump alone delivers enough heat to maintain the setpoint. Backup heat should not run. If your thermostat’s auxiliary-heat stage kicks on above this temperature, the system is either undersized or the staging is misconfigured.
Below the balance point: The pump runs at full output but still cannot keep up with heat loss. Supplemental heat (electric resistance, gas furnace, or a second stage) must make up the shortfall. The greater the gap between the outdoor temperature and the balance point, the more backup capacity is needed.

Sizing the supplemental heat

To find how much backup capacity is required at your design outdoor temperature, subtract the heat pump’s capacity at that temperature from the design heat loss:

backup needed = design heat loss − pump capacity at design temperature

For example, a 30,000 BTU/h design loss with a pump delivering 18,000 BTU/h at the design outdoor temperature needs 12,000 BTU/h of supplemental heat at minimum.

The UA value explained

The UA value the tool reports is the building’s overall heat loss coefficient in BTU per hour per degree Fahrenheit of temperature difference. It combines the thermal resistance of walls, windows, roof, and infiltration into a single number. A higher UA means the building loses heat faster and produces a steeper heat-loss line, which shifts the balance point to a warmer temperature. Improving insulation or air-sealing reduces UA and lowers the balance point, meaning the pump carries the load further into cold weather before backup heat is needed.

Cold-climate heat pumps and the balance point

Variable-speed cold-climate heat pumps (sometimes marketed as hyper-heat or cold-climate ASHPs) maintain meaningful capacity at temperatures well below zero degrees Fahrenheit. For these units, the balance point may be lower than the design outdoor temperature, meaning backup heat is rarely needed — or sized only for extreme cold events. Use manufacturer-published capacity data at the specific low-temperature rating points (commonly 5 °F and -13 °F) when filling in the two data points for cold-climate systems.