HSPF to HSPF2 calculator

HSPF2 is a heat pump's heating efficiency under the test that took effect on January 1, 2023. HSPF is the same idea under the old test. There is no exact formula between them, but AHRI publishes an average factor for each type of equipment, and this calculator applies it in either direction.

The factors

Each factor is the new rating divided by the old one. To go from HSPF to HSPF2, multiply; to go back, divide. If you don't know the type, use the ducted split system row: it covers most central heat pumps, and it is the default the source itself prescribes.

Quick conversion tables

A check you can do yourself

Since January 1, 2023, a split-system heat pump has to reach at least 7.5 HSPF2. The Bonneville Power Administration lists that minimum as equivalent to 8.8 HSPF under the old test. With the ducted split factor: 8.8 × 0.85 = 7.48, which rounds to 7.5.

BPA's table gives ductless heat pumps the same pair of figures, because the federal minimum is one number for every split system, ducted or not. The ductless factor of 0.90 is a narrower estimate for that type of equipment alone, so the two do not contradict each other. They answer different questions.

Why there is no exact formula

HSPF and HSPF2 are not two units for the same measurement, like inches and centimetres. They are the results of two different tests of the same equipment. The best-known change in the new test is a higher external static pressure, the resistance the ductwork puts up, of up to five times the old value. AHRI says the combined effect of the changes is that the new ratings come out numerically lower.

Ductless units have no ducts, which is consistent with their smaller drop. But the test changed in other ways too, and how far a particular unit's number falls depends on how that unit copes with the new conditions. A single factor is an average across equipment, not a rule every unit follows. It is what HERS energy rating software uses to put a new rating on the old scale when the old one is not available.

When not to convert

If the equipment is on sale now, look up the real figure. Anything certified from 2023 on has an HSPF2 on its AHRI certificate. For ducted heat pumps it depends on the indoor unit the outdoor unit is paired with: on the EPA's ENERGY STAR list, 2,444 of 5,521 outdoor models (44.3%) are certified at more than one HSPF2. Converting a brochure's HSPF gives you one number for what is really a range.

A converted figure is not a certified rating. BPA, for example, checks units made before 2023 against the HSPF on their AHRI certificate. If a rebate or a code sets a minimum, check which rating it asks for.

Where the factor does help: putting an old unit rated in HSPF next to a new one rated in HSPF2, to see roughly how far apart they are. Once both are in HSPF2, therunning cost formula turns the difference into dollars at your electricity rate.

Related

• Why one outdoor unit has several HSPF2 ratings
• How to find and check the AHRI certificate number
• Running cost calculator by certified pairing

Sources

• Factors: RESNET MINHERS Addendum 71f, SEER2 and HSPF2 Conversions, Table 4.4.4.1(1), approved February 10, 2023. RESNET states that the factors were developed by AHRI, and that they default to the ducted split system row when the type is not known.
• The test change and its effect: AHRI, 2023 energy efficiency standards.
• Federal minimum and its old-test equivalent: Bonneville Power Administration, Current Federal Minimum Efficiency Standards for Ductless Heat Pumps and Ducted Air-Source Heat Pumps (October 27, 2023).
• Models with more than one HSPF2: U.S. EPA, ENERGY STAR Certified Ducted Heat Pumps, retrieved 2026-09-26. How we grouped and counted it.

By Adrián Criado · About the author and this dataset · Factors checked against the RESNET table on 2026-10-02