SEER2, HSPF2, and Which Numbers Actually Matter
Efficiency ratings are real but they are lab numbers. What they mean, and the specification that matters more than any of them in a cold climate.
By Chris Wheeler, Co-owner ·
Every quote you get will have ratings on it. Here is what they mean and how much weight to put on each.
The main three
SEER2 measures cooling efficiency across a simulated season. Higher is better. It is a seasonal average, not a fixed measure, so it accounts for the equipment running at part load most of the time rather than flat out.
HSPF2 is the heating equivalent. Higher is better. This is the one that matters most here, because we heat far more than we cool.
EER2 measures cooling efficiency at one specific hot condition rather than across a season. Useful for comparing performance on design day.
The “2” on all of these means the current test procedure, which replaced the older SEER and HSPF ratings at the start of 2023. The new tests use higher external static pressure, which is a better approximation of a real duct system. A 2 rating is not directly comparable to an old non-2 rating on the same equipment. If you are comparing an old quote to a new one, make sure you are not comparing across the change.
The number that matters more here
Capacity at low temperature.
Efficiency ratings are seasonal averages built on a national test procedure. They do not tell you what the machine does at five below zero in Concord in January.
What you want from the manufacturer’s data, and what a good contractor will show you, is the extended capacity table. It lists rated heating output at various outdoor temperatures. Look at the row for your design temperature.
A system rated for 36,000 BTU at 47 degrees might deliver 22,000 at 5 degrees. That is not a defect, that is physics, and every heat pump does it. What varies enormously between models is how gracefully. Cold climate rated equipment holds a much larger fraction of its rated capacity down low, and that is what determines whether you are on expensive backup heat for three weeks every winter or three days.
Two systems with the same HSPF2 can behave very differently at zero. Ask for the low temperature capacity, not just the sticker rating.
Where the ratings mislead
They assume correct installation. A high efficiency system installed with undersized ductwork, a bad charge, or a poor commissioning will underperform a mid tier system installed properly. Installation quality swings real world performance more than the difference between two adjacent efficiency tiers.
They assume correct sizing. An oversized high efficiency unit cycling all spring is not delivering its rated seasonal efficiency, because the rating assumes it is running in the range it was designed for.
They average a national climate. Our heating season is longer and colder than the test’s assumptions, and our cooling season is shorter.
How to actually use them
Use ratings to narrow the field, not to pick the winner. My honest ranking of what determines your comfort and your bills:
- Correct sizing, from a real load calculation
- Quality of the installation and commissioning
- Low temperature capacity of the specific model
- Efficiency rating
- Brand
That order surprises people. It should not. I have seen mid tier equipment installed carefully outperform premium equipment installed carelessly, many times.
On paying up for efficiency
Higher tiers cost more. Whether the premium pays back depends on how much you run it, what you pay per kilowatt hour, and how long you keep the house. In a house that runs the system hard for a long heating season, the better equipment usually earns it. In a vacation property used six weekends a year, it will not.
There is a comfort argument too, separate from the money. Higher end equipment generally modulates over a wider range, which means steadier temperatures and better dehumidification, not just lower bills. Some people care about that more than the payback math and that is a fine reason to buy it.
If you want help reading a quote you already have, bring it by. We will walk through the model numbers with you even if you end up going with the other company.