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SEER2 vs. HSPF2: What Each Heat Pump Rating Means in Maine

October 28, 2026
SEER2 vs. HSPF2: What Each Heat Pump Rating Means in Maine

SEER2 and HSPF2 are not rivals. They rate the same heat pump in two different jobs. SEER2 scores how efficiently it cools in summer, and HSPF2 scores how efficiently it heats over a winter season. In Maine, where heating is the main expense, HSPF2 deserves most of your attention. Even then, it is only part of the picture, because neither number tells you how a unit performs on a night at −10°F.

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TL;DR

  • SEER2 is cooling, HSPF2 is heating. Both are seasonal efficiency scores for heat pumps, and a higher number means less electricity used for the same comfort.
  • The "2" means a newer test, not a worse machine. SEER2 and HSPF2 replaced SEER and HSPF in 2023, and the new numbers are not directly comparable to the old ones.
  • For Maine, check low-temperature capacity too. HSPF2 is averaged over a standard heating season, so ask for output at 5°F and for a heat-loss-based sizing.
  • Compare like with like. Put SEER2 next to SEER2 and HSPF2 next to HSPF2, using each manufacturer's certified ratings.

Table of Contents

What SEER2 and HSPF2 actually measure

Both ratings are ratios of output to electricity used across a whole season, not at a single moment.

SEER2 (Seasonal Energy Efficiency Ratio 2) is the heat removed from a space over a cooling season, in Btu, divided by the electrical energy consumed, in watt-hours. That definition comes from the ENERGY STAR key product criteria, which follow the federal test procedure known as Appendix M1.

HSPF2 (Heating Seasonal Performance Factor 2) is the seasonal heating a home requires divided by the electrical energy consumed. The same ENERGY STAR page specifies that this is calculated for "Region IV," a standard heating-season profile. Keep that detail in mind. Region IV is a national reference climate, and it is much milder than a Penobscot County January.

In plain terms:

RatingModeWhat it tells youWhere it falls short
SEER2CoolingSummer efficiency over a seasonSays nothing about heating
HSPF2HeatingWinter efficiency over a standard seasonAveraged, so it hides cold-weather output
EER2Cooling at peak heatEfficiency at one hot-day conditionNot a heating figure
COPHeating at one temperatureEfficiency at a stated point, such as 5°FA single snapshot, not a season

A higher number is better for each. A heat pump with a higher HSPF2 delivers more heat per kilowatt-hour over the standard season. You can't compare a SEER2 figure to an HSPF2 figure, because they measure different things on different scales.

SEER vs. SEER2 and HSPF vs. HSPF2: what changed

The Department of Energy introduced the new metrics for central air conditioners and heat pumps effective January 1, 2023. According to DOE's standards FAQ, the changes were made so the ratings better reflect real-world installation and use. Units manufactured on or after that date must meet the new nationwide standards.

The key change is the test, not the equipment. The federal test procedure rule behind Appendix M1 does three relevant things:

  1. It sets higher external static pressure requirements for all units. That is closer to the airflow resistance of real ductwork.
  2. It revises the heating load line equation and the variable-speed heat pump tests.
  3. It adds a 5°F test option for calculating full-speed performance below 17°F.

The result is that the same physical machine gets a lower number under the new test. New York's clean heat program puts it plainly in its air source heat pump fact sheet: M1 ratings are typically lower because of the testing procedure, and a lower value does not mean the equipment performs worse.

So a heat pump advertised at an HSPF2 of 7.5 is not necessarily less capable than an older one advertised at HSPF 8.2. The two numbers come from different tests. DOE says directly that the new ratings are not directly comparable to the old ones, and that compliance with the standards is judged using the new ratings.

The test was updated again later. DOE incorporated the industry's AHRI 210/240-2024 standard into Appendix M1, and it determined the amendments would not alter measured efficiency. You don't need to track those revisions to shop. Just make sure every rating you compare is a "2" rating.

Why you still see the old names

Contractor quotes, old spec sheets, utility pages and rebate documents sometimes still say SEER or HSPF. If a document lists a SEER or HSPF figure, check whether it is a pre-2023 value. Appendix M values are SEER and HSPF, while Appendix M1 values are SEER2 and HSPF2. Never rank a unit with an old-style figure against one with a new-style figure on the number alone.

What the federal minimums look like

Since 2023, heat pumps sold in the U.S. must clear regional minimums. One industry reference, The HVAC Standard, lists the northern-region minimum for a split-system heat pump as 14.3 SEER2 and 7.5 HSPF2. That includes Maine. It also notes that ENERGY STAR's newer criteria for split heat pumps are higher.

Treat the federal minimum as a floor. It is the least a manufacturer is allowed to sell, not a target for a home that burns through a lot of heating fuel each winter.

Which number matters more in Maine

If you are choosing between two heat pumps for a Maine house, rank them in this order:

  1. Cold-climate capability. Can it deliver most of its rated heat at 5°F and below?
  2. HSPF2. It is your best single seasonal heating number.
  3. SEER2. Useful if you will run cooling, but it should not drive the decision.

Most Maine homeowners use cooling for a few weeks a year, if at all, while heating runs for months. That is why a high SEER2 on its own tells you very little about your bills.

Why HSPF2 is not enough

HSPF2 is an average. A heat pump spends much of a standard season in mild conditions, where nearly any modern unit looks good. Maine's expensive hours are the cold ones. ENERGY STAR's Cold Climate specification recognizes this: cold climate heat pumps are credited for high heating capacity at low temperatures, such as 5°F, rather than for seasonal efficiency metrics alone.

The program's key product criteria set the bar. To earn the Cold Climate designation, a unit needs a COP of at least 1.75 and a capacity of at least 70% of its 47°F capacity when it is 5°F outside. Two heat pumps can share an HSPF2 and behave very differently on a −5°F morning.

When you compare units, ask for these figures in writing:

  • Rated heating capacity at 47°F and at 5°F
  • Whether the model is listed as cold climate
  • The lowest temperature at which it still produces its published output
  • The HSPF2 and SEER2 for the exact indoor and outdoor combination being quoted

The last point matters because ratings apply to a specific matched system, not to a brand name.

A rating won't fix a bad design

Efficiency labels are measured in a lab. Your home loses heat through its walls, windows, attic and air leaks, and that loss is what the heat pump has to match. An oversized unit cycles badly. An undersized one leaves you leaning on backup heat on the coldest nights, which is what drives bills up.

Home heat-loss paths and sizing outcomes

That is why we size from a room-by-room heat-loss calculation, not from square footage or from what the old furnace was. Our articles on planning for heat pump capacity at 5°F and on sizing and commissioning inverter heat pumps go into the method. A mid-range unit that is sized and commissioned properly will usually serve you better than a top-rated unit that is the wrong size.

Perspective: how we read the numbers

We install cold-climate heat pumps in Maine homes, and we read a spec sheet differently than a national shopping guide does. A few rules we follow:

  • We start with the house, not the badge. A heat-loss calculation tells us how many Btu the home needs at design temperature. Only then do we look at models.
  • We treat HSPF2 as a tiebreaker. Once two units both perform at low temperatures and both fit the load, the higher HSPF2 is a reasonable way to choose.
  • We ignore SEER2 for most heating decisions. It becomes relevant when a family wants real summer cooling from the same equipment.
  • We ask what happens after day one. A dirty coil or a clogged filter can erase the difference between a 9 and a 10 on a label. That is why we pair installation with a maintenance plan.

The state has been betting on this technology. Maine has set a target of 275,000 heat pumps installed by 2027, and the state describes high-performance heat pumps as working well in cold climates. That matches what we see, as long as the system is chosen and sized for cold weather.

— John

How to compare two quotes using these ratings

Here is a practical way to put two proposals side by side.

  1. Confirm the rating generation. Both quotes should list SEER2 and HSPF2, not SEER and HSPF.
  2. Match the system type. Compare ductless with ductless and ducted with ducted. Test conditions differ.
  3. Check low-temperature output. Look for the 5°F capacity and any cold climate listing.
  4. Ask how it was sized. A real heat-loss calculation should be part of the proposal. If the answer is "we go by square footage," be cautious.
  5. Verify the ratings. Match the model numbers on the quote against the manufacturer's certified literature and the ENERGY STAR product listing.
  6. Ask about rebates early. Program rules often depend on the model and on your household, so a rated unit may or may not qualify.

Do higher ratings save money?

They can, but with diminishing returns. Going from a minimum-standard unit to an efficient cold-climate unit usually matters more than going from a very good one to a slightly better one. Your savings also depend on what you are replacing, such as oil, propane or electric baseboard, and on how well the home is insulated. Our guide on switching from oil to a heat pump in cold climates walks through that math for homes that will stay put for several years.

Rebates and ratings

Efficiency Maine administers the state's heat pump incentives, and the state has said it will administer federal funds supporting heat pump installations. Eligibility generally turns on the equipment being a qualifying cold-climate model and on your household's circumstances, not on a SEER2 number you picked yourself. Amounts and rules change, so check the current terms before you commit. We keep a page on Maine heat pump rebates that explains how the rebates fit with a project.

Keeping the rating you paid for

A label rating is what a clean, correctly charged, correctly commissioned unit can do. Over time, dust on the indoor coil, a dirty outdoor coil, and blocked airflow all pull real performance below it. Maine adds its own wear: snow, ice and blown debris around outdoor units. If you are curious how long a unit should last, our piece on heat pump lifespan in Maine covers it.

If you want help keeping a system at its best, we offer:

  • A one-time deep cleaning, from $249
  • The Annual Cleaning Plan at $219 per year
  • The Maine Heat Pump Care Plan at $319 per year

The two plans are described on our plans page, and the terms are on the care plan terms page. If you are planning a new installation or replacing an existing unit, our installation planning page explains how we size and select a system. We confirm service by ZIP code before scheduling or taking payment.

FAQ

Is SEER2 or HSPF2 more important for a heat pump in Maine?

HSPF2 matters more, because heating drives most of the annual energy use in Maine. Even so, look past it to the heating capacity at 5°F, since HSPF2 is averaged over a standard national heating season. SEER2 becomes more important if you plan to rely on the unit for summer cooling.

Is a SEER2 rating lower than a SEER rating for the same unit?

Usually, yes. The new test conditions, including higher external static pressure, tend to produce lower numbers for the same equipment. New York's heat pump guidance notes that this lower value does not mean the equipment performs worse.

Can I compare HSPF and HSPF2 numbers directly?

No. DOE says the new ratings are not directly comparable to the old ones. When you compare models, use HSPF2 for both, or ask the installer for the current-test rating of any older unit.

Do I need a heat pump with a SEER2 and HSPF2 rating at all?

Any central heat pump sold in the U.S. since 2023 carries these ratings, so you will see them on every spec sheet. They are useful for comparing efficiency, but for a Maine home also confirm the unit is a cold climate model and is sized from a heat-loss calculation.

Sources