HSPF to HSPF2 converter

What is the HSPF to HSPF2 conversion formula?

HSPF2 measures heat pump heating efficiency under the DOE 2023 M1 test procedure. To convert a legacy HSPF rating to its HSPF2 equivalent, multiply by 0.85. Going the other direction, divide HSPF2 by 0.85 to get the legacy HSPF value. So an old HSPF 10 heat pump rates about HSPF2 8.5 on the new test, and a new HSPF2 8.1 heat pump rates about HSPF 9.5 on the old test stand. The 15 percent drop is consistent across split heat pumps, mini split heat pumps, and single-package heat pumps.

Unlike SEER to SEER2 where the multiplier varies by equipment type (0.95 split AC, 0.93 split heat pump, 0.92 single-package), HSPF to HSPF2 uses the same 0.85 multiplier across all heat pump categories because the heating load test is more uniform than the cooling load test.

HSPF to HSPF2 conversion chart for common heat pump ratings

Quick lookup table for any U.S. residential heat pump. Multiply HSPF by 0.85 to get the HSPF2 equivalent.

• HSPF 7.7 = HSPF2 6.55 (below current federal minimum)
• HSPF 8.0 = HSPF2 6.80
• HSPF 8.2 = HSPF2 6.97 (old federal minimum, no longer compliant)
• HSPF 8.5 = HSPF2 7.23
• HSPF 8.8 = HSPF2 7.48 (right at the new federal floor)
• HSPF 9.0 = HSPF2 7.65
• HSPF 9.5 = HSPF2 8.08 (close to Energy Star minimum)
• HSPF 10.0 = HSPF2 8.50 (cold-climate target)
• HSPF 11.0 = HSPF2 9.35
• HSPF 12.0 = HSPF2 10.20
• HSPF 13.0 = HSPF2 11.05 (premium cold-climate, Mitsubishi Hyper-Heat range)

Federal HSPF2 minimum for new heat pumps

Since January 1, 2023, every residential heat pump sold for new install in the U.S. has to meet HSPF2 7.5 at a minimum. There is no regional split for HSPF2 the way there is for SEER2, meaning a heat pump in Maine has to meet the same heating efficiency floor as one in Texas. Heat pumps also have to meet SEER2 14.3 cooling efficiency to qualify for new install. Below those two numbers, the unit cannot legally be installed.

A heat pump rated HSPF 8.2 under the old standard converts to HSPF2 6.97, which is below the current federal floor. That is why old inventory from before 2023 became hard to install in most jurisdictions. Sell-through dates varied by region, but new manufacturing must hit the HSPF2 minimums.

Energy Star HSPF2 threshold for tax credits and utility rebates

Energy Star sets a tighter HSPF2 standard than federal code. The current Energy Star minimum is HSPF2 8.1 for split heat pumps and HSPF2 7.5 for single-package units. Most state and utility rebate programs use Energy Star as their floor, which means a unit at the federal minimum HSPF2 7.5 will not earn you any rebate dollars. To qualify for the typical $300 to $1,500 utility heat pump rebate, look for HSPF2 8.1+.

For the bigger HEAR (Home Electrification and Appliance Rebates) program payouts of $4,000 to $8,000, the qualifying threshold is HSPF2 8.5 paired with SEER2 15.2. Cold-climate state rebates from Mass Save, NYSERDA, and Efficiency Maine often require HSPF2 9+ for the highest rebate tiers. Always check the rebate program's specific equipment list before you commit.

What HSPF2 rating do you need by climate zone?

HSPF2 matters more the further north you go. In southern states a heat pump might run heating 300 hours a year, while in northern states it runs 1,500+ hours. The same percentage gain in HSPF2 gives you five times the dollar savings in cold climates. Target HSPF2 ranges by climate:

• Zone 1 to 2 (hot, almost no heating needed): HSPF2 7.5 to 8.0 is fine
• Zone 3 (warm, mild winter): HSPF2 8.0 to 8.5
• Zone 4 (mixed, real winter): HSPF2 8.5 to 9.0
• Zone 5 (cool, regular cold snaps): HSPF2 9.0 to 9.5
• Zone 6 to 7 (cold, sustained cold): HSPF2 9.5 to 11.0 with cold-climate inverter

In zones 6 and 7, the heat pump tier matters more than the brand. Mitsubishi Hyper-Heat, Daikin Aurora, and Bosch IDS Premium Connected hold their HSPF2 high enough to handle real cold without backup resistance heat kicking in. Standard heat pumps below HSPF2 8.5 will lose serious capacity below 25 degrees Fahrenheit and force the strip heat to run.

HSPF2 vs COP: what is the difference?

HSPF2 is a seasonal average. COP (coefficient of performance) is a single-temperature snapshot. HSPF2 8.1 means the heat pump delivered 8.1 BTU of heat per watt-hour of electricity over the full heating season including the warmer and colder days. COP at 47 degrees might be 3.5, COP at 17 degrees might be 2.0, and the HSPF2 number bakes both into one figure.

For shopping, HSPF2 is the right number to compare across brands. For sizing a system to your specific climate, ask the contractor for the COP curve from the manufacturer's spec sheet. Carrier, Trane, and Lennox publish full COP-vs-outdoor-temperature tables for every heat pump model. That curve tells you what the unit actually delivers on a 10-degree morning in your climate, which HSPF2 alone cannot.

Why HSPF2 numbers look so much lower than HSPF

HSPF2 drops nearly 15 percent from legacy HSPF because the M1 test runs the heat pump against five times the external static pressure of the old test (0.5 inches of water column vs 0.1). That extra static pressure penalty is closer to what a real heat pump experiences in a home with ductwork, return air filters, and bends in the ducts. The unit did not get less efficient overnight when the rating changed. The test just got more honest.

SEER2 dropped about 5 percent, HSPF2 dropped about 15 percent. Heating mode is hit harder because the heat pump's heating capacity is more sensitive to airflow than its cooling capacity. If you see an old HSPF 10 heat pump in your specs and a new HSPF2 8.5 heat pump next to it, the new unit is actually slightly more efficient because HSPF 10 converts to HSPF2 8.5.

How HSPF2 affects your annual heating bill

Rough rule for a 3-ton heat pump heating a 1,800 sq ft home in a mixed climate at $0.18 per kWh: every 1.0 increase in HSPF2 cuts your annual heating bill by about $80 to $140. In a cold climate it can cut it $200 to $400. The annual bill impact compounds over a 12 to 15 year equipment life. The upgrade from HSPF2 7.5 to HSPF2 9.5 over the equipment lifetime is usually $1,500 to $4,500 in heating bill savings, which is well above the price premium for the higher-rated unit.