Use this free heat pump size calculator as a sanity check before comparing equipment. If you already have a Manual J heating load, enter it for a stronger comparison. If you do not, the calculator can produce a broad screening range from your home size and building assumptions.
Heat Pump Size & Cold-Weather Capacity Calculator
Enter what you know. The calculator will use a Manual J heating load when provided; otherwise it will create a broad preliminary range and clearly label it as an estimate.
Your Heat Pump Sizing Check
How the Preliminary Sizing Range Is Calculated
When you do not enter a Manual J heating load, this tool uses a deliberately broad screening heuristic rather than a recognized load-calculation standard. The starting ranges are expressed in BTU/h per square foot and vary by the winter profile selected: mild 18–28, cool 22–32, cold/high-elevation 26–38, and very cold 30–45.
The tool then adjusts that broad range for the insulation/air-sealing selection, window/exposure selection, and ceilings above 8 feet. Those adjustment factors are there to make the sanity check more responsive to obvious building differences; they are not ACCA Manual J factors and should not be used to select equipment.
If you enter a Manual J heating load, the square-foot screening estimate is bypassed. The calculator instead scales that entered design load to 17°F and 5°F using a simple temperature-difference relationship, then compares those estimated loads with the manufacturer capacity values you enter.
Use this output to identify questions, not to choose tonnage. Final equipment selection should use the actual residential load calculation, design conditions, manufacturer performance data, and the system-selection process used by the contractor.
What Size Heat Pump Do I Need?
Square footage is useful for a rough first pass, but it is not enough to select a heat pump. Residential heating load changes with outdoor design conditions, insulation, air leakage, windows, ceiling height, ducts, building orientation, and other factors.
For final equipment selection, ask for a residential load calculation and the proposed unit’s manufacturer performance data at the temperatures that matter for your climate. Our heat pump sizing and Manual J guide explains what to ask for.
Why Cold-Weather Capacity Matters More Than Nominal Tonnage
A “3-ton” heat pump is a nominal equipment size. It does not tell you exactly how much heating capacity the unit will provide at 17°F, 5°F, or another winter condition. That is why this calculator lets you enter low-temperature manufacturer capacity separately from nominal size.
See cold-climate heat pumps and how heat pumps behave in cold weather for more context.
How to Use a Contractor Quote With This Calculator
- Enter the Manual J heating load if your contractor supplied one.
- Enter the proposed nominal system size.
- Find the manufacturer’s heating capacity at 17°F and 5°F or the closest available low-temperature data.
- Compare those capacity values with the estimated load.
- Ask how backup heat will cover any capacity gap.
Heat Pump Size Calculator FAQs
Can you size a heat pump by square footage?
Square footage can support a rough screening estimate, but final sizing should use a residential load calculation that accounts for the actual building and local design conditions.
How many BTUs are in one ton of heat pump capacity?
One nominal ton equals 12,000 BTU per hour. Nominal tonnage should not be confused with the heat pump’s actual heating output at low outdoor temperatures.
Why enter heat pump capacity at 17°F and 5°F?
Low-temperature performance helps show whether a proposed heat pump continues to cover the home’s heating requirement as outdoor temperatures fall.
Does this replace Manual J?
No. This tool is designed for homeowner screening and quote comparison. A final system should be based on a proper load calculation and equipment-selection process.
Need a Local Heat Pump Quote?
If the property is in Kachina Village, Flagstaff, or a nearby covered area, you can also request a heat pump installation quote.