Cold climate heat pump sizing means selecting equipment on its heating capacity at your heating design temperature, not on its nameplate tons. A heat pump's output falls as the outdoor temperature drops, so, for example, a unit that delivers 36,000 BTU/h at 47°F may deliver much less at 0°F. Start with a Manual J heating load, read the equipment's capacity at the design temperature from manufacturer data or the NEEP listing, and either cover the full load or design a balance point with backup heat.
This guide is in outline form. The full version will include a worked example with a capacity curve and balance point.
In this guide
Why nameplate tons mislead
- Rated capacity at 47°F vs maximum capacity at 17°F, 5°F and your design temperature.
- Reading NEEP product listings and manufacturer extended data.
- NYS Clean Heat: "Sizing shall not be based on nominal size or AHRI rated capacities."
The load at design temperature
- 99% heating design temperatures and where to find them.
- Why padding the load backfires on variable-speed equipment.
- Run the load first: see the Manual J guide.
Full-load vs balance-point designs
- NEEP's guidance: 100 to 115% of the heating load at design, or a balance point of 20°F or below with auxiliary heat.
- Choosing backup: electric resistance, existing boiler or furnace, or none.
- Integrated controls and switchover temperatures.
Rebate sizing rules side by side
- NYS Clean Heat: at least 100% of building heating load, justification above 120%, at least 80% of conditioned floor area served. See NYS Clean Heat for contractors.
- Mass Save: 90 to 120% of total heating load at design throughout 100% of conditioned space. See Mass Save for contractors.
Multi-zone and ductless systems
- Sizing each outdoor unit on the block load for its zones.
- Head sizing from room loads, and minimum turndown.
Cooling in a heating-dominated home
- Checking cooling capacity and latent removal once heating sets the size.
Estimate, then design
The heat pump sizing calculator estimates load and nominal size by ZIP code, and the mini split sizing calculator suggests per-zone head sizes. Both are estimates only.
Tradewright selects real equipment on capacity at your design temperature and generates the documentation NYS Clean Heat and Mass Save ask for. See equipment selection and rebate documentation.
Questions
How do you size a cold climate heat pump?
Run a Manual J to get the heating load at the 99% heating design temperature. Then look up the heat pump's maximum heating capacity at that temperature in the manufacturer's data or the NEEP listing, and select a system whose capacity at design meets the load, or design for backup heat below a chosen balance point.
What sizing range does NEEP recommend?
For full HVAC replacement, NEEP's sizing guide suggests matching system capacity at the design temperature to 100 to 115% of the estimated heating load without auxiliary heat, or designing for auxiliary heat at a balance point of 20°F or below.
What sizing does NYS Clean Heat require?
Full-load systems must meet at least 100% of the building heating load at design conditions and serve at least 80% of the conditioned floor area. Systems above 120% of the heating load in heating-dominated projects need a sizing justification letter. Equipment sizing must use manufacturer extended performance data, not nominal size or AHRI rated capacity.
What sizing does Mass Save require?
Mass Save's whole-home verification form and partial-home sizing bonus require equipment sized to meet 90 to 120% of the total heating load at the outdoor design temperature, per ACCA Manual J design conditions, throughout 100% of the conditioned space.
What is a balance point?
The balance point is the outdoor temperature at which the heat pump's heating capacity equals the home's heat loss. Below it, the heat pump alone cannot keep up and backup heat makes up the difference.
Does a heat pump need to be on the NEEP list?
For NYS Clean Heat, air-source heat pumps must be on the NEEP cold climate list or meet the program's criteria for equipment the list does not cover. Mass Save requires equipment that meets ENERGY STAR Cold Climate, per its own qualified products list.
Sources
- NEEP: Guide to Sizing and Selecting Air-Source Heat Pumps in Cold Climates (accessed 2026-10-16)
- NEEP: Cold Climate Air Source Heat Pump product list (accessed 2026-10-16)
- NYS Clean Heat Heat Pump Program Manual, Version 3 (September 1, 2026), Sections 3.1.1 and 3.2 (accessed 2026-10-16)
- Mass Save: Air Source Heat Pump rebates and eligibility (sizing bonus) (accessed 2026-10-16)