HSPF Rating Explained: HSPF vs HSPF2 and Seasonal Heat Pump COP

What HSPF measures

Heating Seasonal Performance Factor is the heating counterpart of SEER. The test measures the heat pump at several outdoor temperatures, weights each by how many hours a reference climate spends there, and adds in the energy for defrost cycles and any electric resistance backup the model needs on the coldest hours.

HSPF = Seasonal heat delivered (BTU) ÷ Seasonal electricity used (Wh)
Seasonal COP = HSPF ÷ 3.412

The 3.412 comes from the fact that 1 watt-hour equals 3.412 BTU. Dividing removes the mixed units and leaves a pure ratio: heat out per unit of electricity in. Electric resistance heat has a COP of exactly 1, so any heat pump with an HSPF above 3.412 beats a baseboard heater over the season, and modern ones beat it by a factor of two or more.

Why HSPF2 reads lower than HSPF

The 2023 test procedure changed three things that all push the number down:

• Higher external static pressure (about 0.5 in. w.c. instead of 0.1 for ducted systems), so the blower consumes more power, just as with SEER2.
• A steeper building load line. The modeled house needs more heat at low temperatures, so the heat pump spends more of the season at cold conditions where it is less efficient, and more backup heat is counted.
• Revised weighting of the climate bins to better reflect real heating seasons.

The result is a drop of roughly 15%. Treat the 0.85 factor as an approximation: units with strong low-temperature capacity lose less in the conversion than ones that lean on backup heat.

HSPF to HSPF2 to COP conversion table

The seasonal COP is an average across the whole modeled winter. On a 47 °F day the same heat pump may run at a COP of 3.5–4, and on a 5 °F night closer to 1.5–2. See heat pump efficiency vs temperature for the full curve.

Federal minimums and efficiency tiers

Since January 1, 2023, DOE requires:

• Split-system heat pumps: 7.5 HSPF2 and 14.3 SEER2, in every region.
• Packaged (single-cabinet) heat pumps: 6.7 HSPF2 and 13.4 SEER2.

The old equivalents were 8.8 HSPF and 8.0 HSPF respectively. ENERGY STAR and utility rebate programs set higher bars; in recent versions the ENERGY STAR level for ducted split heat pumps has been around 7.8 HSPF2, with a cold-climate tier around 8.5 HSPF2 plus a minimum COP at 5 °F. Check the current program version before buying, since tiers change and rebate amounts often depend on them.

Turning HSPF2 into a heating bill

If you know roughly how much heat your home needs in a season, HSPF2 converts it straight to kilowatt-hours:

Seasonal kWh = Seasonal heat needed (BTU) ÷ (HSPF2 × 1,000)

Example: a home that needs 40 million BTU of delivered heat a year (a moderate amount for a 2,000 sq ft house in a mixed climate) uses 40,000,000 ÷ 7,500 = 5,333 kWh with a 7.5 HSPF2 heat pump, or 40,000,000 ÷ 9,000 = 4,444 kWh at 9.0 HSPF2. The 889 kWh difference is worth about $151 a year at $0.17/kWh. The same heat from baseboard or an electric furnace would take 11,723 kWh.

For month-by-month estimates with your own load, hours and COP, use the heat pump running cost calculator, and to compare with gas, see gas vs electric heating.

Comparing HSPF2 with furnaces and resistance heat

Seasonal COP lets you put a heat pump on the same footing as other heating. Electric resistance heat has a COP of 1. A gas furnace's AFUE is its fuel-to-heat efficiency, so a 95% furnace is the fuel equivalent of a COP of 0.95, but it burns gas rather than electricity, so the cost comparison depends on both prices.

The last column is 1,000,000 ÷ (HSPF2 × 1,000) for heat pumps, or 1,000,000 ÷ 3,412 for resistance heat. Multiply by your price per kWh to get the cost of each million BTU of heat.

What HSPF2 doesn't tell cold-climate buyers

The rating is calculated for a single reference climate (DOE climate region IV, roughly a mid-Atlantic or lower Midwest winter). If you live in Minnesota, Maine or the mountain West, two heat pumps with the same HSPF2 can behave very differently on a −5 °F night. For cold climates, look at:

• Capacity at 5 °F as a share of capacity at 47 °F. Cold-climate models typically keep 70% or more.
• COP at 5 °F, ideally 1.75 or higher.
• Minimum operating temperature before the compressor shuts down (see heat pump temperature range).

Size a heat pump for your heating load, not just cooling, if you want it to carry the house through most of the winter. The heat pump sizing calculator walks through the balance point.

Frequently asked questions