Heat pump balance point calculator
Enter the design load and the heat pump's capacity at 47, 17 and 5°F. Get the thermal and economic balance points, backup kW at design, a dual-fuel switchover and how many hours a typical year spends below balance.
- Free, no sign-up
- Runs in your browser
- Estimate: shows its formulas
House
99% heating and 1% cooling dry bulb, from ASHRAE Handbook—Fundamentals design conditions via Climate.OneBuilding.org. Your local code may set its own values.
Heat pump
Generic, illustrative curves. For a real proposal, enter the model's extended performance data (maximum capacity at 47, 17 and 5°F).
Running costs
Use the delivered price from a recent bill, including delivery charges. Defaults are placeholders, not local rates.
Results
Estimate from your inputs · updates as you type
- Thermal balance point
- 19°F
- Below this, backup heat runs
- Electric backup at design
- 3.9 kW
- 13,400 BTU/h · next common heat kit: 5 kW
- Heat pump at design
- 28.6k BTU/h
- 68% of the 42.0k load
- Economic balance point
- 30°F
- Heat pump COP below 2.98 costs more than natural gas
Suggested dual-fuel switchover
30°F
Set by running cost: above the thermal balance point (19°F), but below 30°F the furnace heats for less.
At 6°F: house needs 42.0k BTU/h, heat pump makes 28.6k · backup 13.4k BTU/h
Over a typical year
Bin method with hourly temperatures for a typical year
- Hours below balance point
- 286
- of 6,286 heating hours
- Heat pump share of heat
- 97%
- with electric backup
- Backup electricity
- 809 kWh
- per typical year
| Setup | Heating cost / year |
|---|---|
| Heat pump + electric backup | $1,507 |
| Dual fuel, switch at 30°F | $1,354 |
| Natural gas furnace only | $1,464 |
Hourly temperatures: Climate.OneBuilding.org TMYx typical year for Denver Intl AP, CO (2011-2025). A typical year has fewer extreme hours than a cold one, so treat these as averages. Seasonal heat uses the same straight load line; no defrost, cycling or duct losses are included.
How the balance point is calculated
The method is the classic one from the ASHRAE Handbook—Fundamentals and the heat pump guidance published by the US Department of Energy and NEEP: a straight load line for the house, a capacity curve for the heat pump, and the points where they cross.
1. The house load line
Heat loss is proportional to the indoor–outdoor temperature difference, so the load is a straight line: zero at the no-heat temperature (where internal and solar gains cover the losses) and the design heating load at the outdoor design temperature.
2. The heat pump capacity curve
Capacity is interpolated in straight lines between the 47, 17 and 5°F points and extended past them along the nearest segment. Use maximum capacity from the manufacturer's extended performance data: a variable-speed unit can deliver well above its rated output in the cold.
3. Thermal balance point and backup heat
The thermal balance point is where capacity meets the load. Below it, backup heat makes up the gap. At the design temperature that gap, in kW of electric heat, is:
4. Economic balance point
Heat from a heat pump costs the electricity price divided by its COP. Heat from a furnace costs the fuel price divided by its efficiency. They cost the same when the COP equals the break-even COP:
Below the temperature where the heat pump's COP falls to that value, the furnace heats for less. A dual-fuel system should switch over at the warmer of the two balance points.
5. A typical year
The seasonal figures use the bin method: each hour of a typical year, from the Climate.OneBuilding.org TMYx weather file for the station you pick, is placed in a 1°F bin, and the load line and capacity curve are run through every bin. Typical years are milder than the coldest years, so treat hours below design as a floor, not a forecast.
What this doesn't include
- Defrost and cycling losses, which lower real output in cold, humid weather.
- Duct losses, altitude derating and how the equipment is actually controlled.
- A load: bring one from a room-by-room Manual J, or estimate it with the heat loss calculator or the HVAC load calculator.
For the full picture, read when to switch a dual-fuel system to the furnace and heat pump sizing, step by step.
Balance point questions
- What is a heat pump balance point?
- The thermal balance point is the outdoor temperature where a heat pump's heating capacity equals the house's heat loss. Above it the heat pump carries the house alone; below it, backup heat (electric strips or a furnace) has to make up the difference.
- What is the economic balance point?
- The outdoor temperature below which heat from the heat pump costs more than heat from the furnace. It depends on electricity and fuel prices, furnace efficiency and the heat pump's COP at that temperature. The break-even COP is the electricity price per kWh × 293.07 divided by the fuel's cost per million BTU of delivered heat.
- What switchover temperature should I set for dual fuel?
- Start at the warmer of the thermal and economic balance points: below the thermal point the heat pump can't keep up, and below the economic point the furnace heats for less. Comfort, utility rate structures and the control's lockout options can move it a few degrees either way.
- How much backup heat does a heat pump need?
- At the design temperature, backup heat should cover the gap between the design heating load and the heat pump's capacity at that temperature. Divide the gap in BTU/h by 3,412 for kW of electric heat. Many installers round up to the next heat-kit size, and some codes or utilities have their own rules.
- Which capacity numbers should I use?
- Use the maximum heating capacity from the manufacturer's extended performance data, or a cold-climate heat pump listing, at 47, 17 and 5°F. Rated (nominal) capacity understates what a variable-speed unit can do and overstates a single-stage unit at low temperatures.
- Is this a Manual J or Manual S calculation?
- No. It takes a design load you supply and compares it with equipment capacity using straight-line approximations. A room-by-room Manual J gives the load, and Manual S selection uses the manufacturer's full performance data at your design conditions.
Balance points from a real load, room by room
This tool starts from a load you already have. calc.blue builds that load: scan the house with an iPad Pro, get room-by-room heating and cooling loads with a likely range, then compare heat pumps and furnaces against the house at its own design temperatures, built on ACCA Manual J 8th edition procedures.