Homeowners shopping for an efficient heat pump are asking about the HSPF2 meaning now that it has replaced HSPF as the rating standard for heat pumps.
HSPF2 is the Heating Seasonal Performance Factor, version 2. The new heat pump heating efficiency rating replaced the original HSPF rating that expired on December 31, 2022.
The Department of Energy (DOE) put this new metric in place in order to make HVAC testing procedures more accurate to real-life conditions.
What is HSPF2?
Like the old HSPF ratings, the HSPF2 ratings determine how energy-efficient a heat pump is while the heat pump warms up your home in Heat Mode. HSPF2 does not determine your heat pump’s cooling efficiency in Cool Mode. The cooling efficiency ratings are EER2 and SEER2.
The new energy efficiency minimum for air-sourced heat pumps is 7.5 HSPF2.
As it was with the HSPF rating, HSPF2 ratings are calculated by dividing a heat pump’s total heating output, which is measured in British Thermal Units (BTUs), by its total watt-hours. For example, if your heat pump uses 8,500 BTUs and 10 kWh (or, 1,000 watts per hour), then it will have an 8.5 HSPF2 rating. (8,500 / 1,000 = 8.5)
Heat pumps with higher HSPF2 ratings are more energy efficient than those with lower HSPF2 ratings. The current range of HSPF2 ratings on available heat pumps is 7.5 HSPF2 to more than 10.0 HSPF2 on the most efficient split system heat pumps from Lennox, Carrier and Bryant.
FYI: A 7.5 HSPF2 is the equivalent of an 8.8 HSPF efficiency rating.
HSPF vs HSPF2
The main difference between HSPF and HSPF2 is under what conditions the HVAC equipment is tested. The testing for HSPF and HSPF2 is similar with one difference: The HSPF2 test is done in conditions that mimic harsher weather conditions that better represent typical conditions heat pumps work under to draw heat from outside air.
For example, both the HSPF and HSPF2 ratings use an external static pressure test, which checks a heat pump’s vent pressure. The DOE determined that the original HSPF conditions for this test were too low for an accurate real-life reading, so the test was modified. Now, the HSPF2 rating test applies 5 times more pressure than the original HSPF test, which means the heat pump’s blower has to work harder to expel air.
Technical info: The old HSPF rating was based on 0.1 inches of water column (in. WC). The new rating is 0.5 in. WC. The in. WC test is a test for external air pressure. The higher rating better replicates high-pressure air. And 1 in. WC is equal to 0.0361 psi or about 2.5 millibar (mbar).
According to this DOE document (see page 236), the harsher testing conditions make HSPF2 ratings approximately 15% lower than HSPF ratings. If you find a listing with HSPF only, the HSPF to HSPF conversion can be done by multiplying the HSPF rating by .85. This means, for example, that a heat pump with an HSPF rating of 10 will now have an HSPF2 rating of 8.5.
Is the original HSPF rating enough?
No, not by itself. Many manufacturers continue to use HSPF but only when they also show the HSPF2 rating.
For compliance to DOE regulations, the HSPF2 ratings are the new standard and must be shown to consumers, replacing the original HSPF rating.
When you shop for a heat pump on a manufacturer’s website, either just the HSPF2 rating should be shown or you should see both HSPF and HSPF2, as in the Lennox example above. Most brands, like Carrier, are showing just the new HSPF2 rating.
What Is a Good HSPF2 Rating on a Heat Pump?
An HSPF2 rating of 7.8 or above is a good HSPF2 rating. However, a good heat pump HSPF2 rating depends on your climate. In a mild climate, a rating of HSPF2 7.5 to 8.2 is a good rating. In colder climates, you’ll want a more energy efficient heat pump. Where winter temperatures drop into the 30s, a good HSPF2 rating on a heat pump is 8.5 to 10.0.
Buying Tip: Energy Star minimum ratings do not reflect super-high efficiency. It’s just the bare minimum to qualify, but there are heat pumps with significantly better efficiency than the minimum criteria.
Our heat pump experts recommend buying a unit for cold climates that is at least 1.0 HSPF2 above the minimum, or 8.5 HSPF2.
Taking all climates together, your heat pump should have an HSPF2 rating somewhere between 8.1 and 10.0 for optimal energy efficiency. According to Energy Star, which is a program run by the EPA and DOE to test all appliances on the market for energy efficiency:
- Non-ducted split system heat pumps with at least an 8.5 HSPF2 rating can qualify.
- Ducted split system heat pumps with at least an 8.1 HSPF2 rating can qualify for an Energy Star label.
- Single-package heat pumps with at least an 8.1 HSPF2 rating can qualify.
To know the best heat pump efficiency rating for your home, get multiple estimates from .
The DOE requires any heat pump equipment to have an efficiency of at least 7.8 HSPF2. For non-ducted systems, often called ductless heat pumps, the minimum is 8.5 HSPF2. For all ducted and package systems, the heat pump minimum efficiency is 8.1.
| Product Type | Specification |
|---|---|
| HP Split Systems (Non-Ducted) | ≥ 8.5 HSPF2/ ≥15.2 SEER2 |
| HP Split Systems (Ducted) | ≥ 8.1 HSPF2/ ≥15.2 SEER2 |
| HP Single Package Equipment | ≥ 8.1 HSPF2/ ≥15.2 SEER2 |
This table is from the Energy Star Heat Pump Key Criteria page.
HSPF2 vs. SEER2
Alongside the original HSPF rating, the DOE updated the Seasonal Energy Efficiency Ratio (SEER) for 2023 and onward. The reason for this is because SEER is just as important for heat pumps as HSPF.
While the HSPF2 rating determines your heat pump’s heating efficiency throughout the colder months, SEER2 indicates your heat pump’s cooling efficiency in air conditioning mode.
And just like HSPF2, the higher your heat pump’s SEER2 rating, the more energy-efficient it is.
SEER2 ratings are roughly 5% lower than the original SEER ratings. This means a heat pump with a 14 SEER rating will now have a 13 SEER2 rating.
With both rating systems being updated, all US manufacturing and HVAC companies must follow the new regional minimum efficiency requirements, sometimes called DOE 2023 rules. These requirements are split between the North US and the South US. The South is also split up into the Southwest and the Southeast. For more on these requirements, see our article here.
