Formula
Solve HP capacity(T) = building load(T) — below this temp, strip / aux heat takes overPull HP capacity at 47°F and 17°F from AHRI cert sheet. Building load is your design heat loss at design outdoor temp.
Building load
Heat pump capacity (AHRI)
Economic crossover
Thermal balance point
23°F
Below this OAT, you need aux heat to meet load
Heat pump $/MMBTU$21.32
Electric strip $/MMBTU$46.89
How to use this calculator
Determine the outdoor temperature where heat pump capacity equals building heat loss.
- Enter the building design heat loss at the design outdoor temperature.
- Enter heat pump capacity at two rating temperatures, typically 47 °F and 17 °F.
- Read the balance point where the capacity line crosses the load line.
- Size auxiliary heat to cover the gap below that temperature.
Frequently asked questions
- What is a heat pump balance point?
- The outdoor temperature at which the heat pump's output exactly matches the building's heat loss. Below it, supplemental heat is required.
- What is a typical balance point?
- Conventional heat pumps usually balance between 25 °F and 35 °F; cold-climate inverter units can stay ahead of the load down to 5 °F or below.
- How much auxiliary heat do I need?
- Enough to cover the difference between design heat loss and heat pump output at the design temperature — no more, since oversized strip heat is expensive to run.