HSPF2 and HSPF: how the 2023 heating efficiency rating differs
HSPF and HSPF2 both measure a heat pump's heating efficiency over a season. HSPF2 is the rating for equipment made from January 1, 2023.
Two ratings, one quantity
Both ratings divide the heat a heat pump delivers over a modeled heating season, in Btu, by the electricity it uses, in watt-hours. Higher uses less electricity.
HSPF comes from the Department of Energy test procedure in Appendix M. HSPF2 comes from Appendix M1. Every rating made on or after January 1, 2023 must use Appendix M1.
What changed on January 1, 2023?
The test airflow changed. External static pressure is the resistance the indoor blower pushes air against, standing in for the ducts in a house. For a ducted system with its own indoor blower, Appendix M set the test minimum at 0.10 to 0.20 inches of water, by size. Appendix M1 sets it at 0.50 for most equipment. Ductless indoor units are tested at zero in both.
A heat pump's HSPF and HSPF2 come from different tests, and the test procedure gives no formula that converts one into the other.
Test airflow: DOE Appendix M, Table 4 and DOE Appendix M1, Table 4.
The federal minimums, before and after
The federal efficiency standards changed on the same date, and the new ones are written in HSPF2. Each column uses its own test.
| Product class | HSPF, made 2015 to 2022 | HSPF2, made from 2023 |
|---|---|---|
| Split-system heat pumps | 8.2 | 7.5 |
| Single-package heat pumps | 8.0 | 6.7 |
Federal minimums: 10 CFR 430.32(c)(1) and (c)(5).
HSPF2 across certified heat pumps
The certified data carries HSPF2 and SEER2, not HSPF or SEER. Each model counts once, by the median of its own pairings. The median HSPF2 is 9.9 for mini-split models and 8.6 for central models. The highest model median is 16.2, and the highest single pairing is certified at 17.5.
| Type | Models | 10th percentile | Median | 90th percentile | Highest |
|---|---|---|---|---|---|
| Mini-split | 5,616 | 8.95 | 9.9 | 11.1 | 16.2 |
| Central | 2,804 | 7.8 | 8.6 | 9.75 | 11.0 |
| All | 8,420 | 8.1 | 9.5 | 10.8 | 16.2 |
HSPF2 is a seasonal figure
HSPF2 is modeled for one climate, DOE climate Region IV. Ratings for other regions are optional and are not in the certified data. The calculation includes the unit cycling on and off, defrost, and the backup resistance heat the model switches on when the heat pump falls short of the load.
It is a seasonal average, so it is not a COP at any one outdoor temperature. HSPF2 ÷ 3.412 gives the seasonal average heating COP for Region IV. The COP in the 5°F full-speed test is a separate certified figure.
What to compare on a quote
An HSPF2 belongs to one outdoor unit paired with one indoor unit, and another indoor unit can change it. Compare the HSPF2 of the exact pairing on each quote. The quote check shows the certified figures for that pairing.
Where to go next
Browse mini-split heat pumps or central heat pumps, compare 12,000 Btu heat pumps or 36,000 Btu heat pumps, or read how SEER2 differs from SEER.