Guide
HSPF2, SEER2 and COP: which number actually matters in Bellingham
HSPF2 is heating efficiency, SEER2 is cooling, COP is efficiency at one moment and one temperature. In a heating-dominated marine climate, here is which one to weight and how the PSE rebate tiers use them.
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Efficiency ratings exist so you can compare equipment, and they get quoted at you in ways designed to end conversations rather than inform them. There are three numbers worth understanding. HSPF2 is a seasonal heating efficiency; SEER2 is a seasonal cooling efficiency; COP is instantaneous efficiency at a stated outdoor temperature, and it is the one that tells you what happens on a cold Bellingham morning. All three changed meaning in 2023 when the M1 test procedure replaced the old one, so old and new numbers are not interchangeable.
The three numbers, in one paragraph each
HSPF2 — Heating Seasonal Performance Factor 2 — is the total heating output over a season divided by the total electricity consumed, in BTU per watt-hour. Because it is seasonal, it bundles mild hours and cold hours and defrost cycles into one figure. Higher is better, and it is the number that most closely tracks your winter bill.
SEER2 — Seasonal Energy Efficiency Ratio 2 — is the same idea for cooling. It matters less here than almost anywhere in the country, because our cooling design temperature is 78°F and climate zone 4C runs 0 to 500 cooling degree days.
COP — coefficient of performance — is the ratio of heat delivered to energy consumed at one specific operating condition, dimensionless. A COP of 3 means three units of heat out for one unit in. Unlike the seasonal figures, a COP is always quoted at a stated temperature, and that is exactly why it is the useful one for cold-weather questions.
Why the "2" matters and old numbers do not compare
In 2023 the US test procedure for these ratings changed. The M1 procedure raised the external static pressure that equipment is tested against, so it better reflects real ducted installations rather than a laboratory ideal. SEER became SEER2, HSPF became HSPF2, and EER became EER2.
The practical effect is that the new numbers are generally lower than the old ones for the same physical equipment. A unit that was 16 SEER may be around 15.2 SEER2, which is not a downgrade — it is a different measurement.
So when a brochure, a review site or a salesperson quotes an HSPF or SEER without the 2, they are quoting the old test. Comparing a 9.5 HSPF2 unit against a 10 HSPF unit as though the second were better is a mistake, and it is a mistake that occurs in the wild constantly.
In a heating-dominated climate, weight HSPF2
Bellingham sits in IECC and ASHRAE climate zone 4C, the marine zone that covers the I-5 corridor west of the Cascades. Zone 4C runs roughly 3,000 to 5,000 heating degree days and 0 to 500 cooling degree days, which is to say heating drives both equipment selection and runtime.
That has a clear implication. Between two units where one has better SEER2 and the other better HSPF2, take the HSPF2 in nearly every Bellingham house. You will run the heating side for most of the year and the cooling side for a handful of weeks.
The exception is a specific room with a large cooling problem — a west-facing bonus room over a garage, a room with substantial south glazing and no shade — where cooling capacity and efficiency genuinely matter. Even then, the whole-house selection should be made on the heating side.
How PSE turns these ratings into money
PSE’s midstream HVAC equipment discount is priced directly off SEER2 and HSPF2 tiers, passed through the distributor rather than mailed to you. It applies to air-source heat pumps under 5.4 tons, including mini-splits and multi-splits, and is limited to one unit per residential retrofit project or two per new-construction project.
The practical decision this creates is at the margins: a unit just below a tier threshold and a unit just above it can differ in price by less than the tier difference, in which case the better equipment is effectively cheaper.
One honest caveat. Whether the midstream discount stacks with PSE’s $1,500 electric-resistance conversion rebate is unconfirmed, and we will not tell you it does. Ask us to confirm both the stacking question and our PSE network status for your project before you count either amount as certain.
| Tier | Eligible project type | Minimum SEER2 | Minimum HSPF2 | Pass-through per unit |
|---|---|---|---|---|
| 1 | Retrofit only | 15.2 | 8.1 | $300 |
| 2 | Retrofit or new construction | 15.2 | 8.5 | $400 |
| 3 | Retrofit or new construction | 16.0 | 9.5 | $600 |
The number that is not on the label
Neither HSPF2 nor SEER2 tells you what the equipment does at 19°F, and that is the question a Bellingham buyer actually has. Seasonal ratings average across a standardised range of conditions; your cold snap is a specific condition.
What you want is the manufacturer’s expanded performance data: capacity in BTU per hour and COP at a series of outdoor temperatures, typically including 47°F, 17°F and 5°F. Those tables exist for every serious piece of equipment and any competent supplier can produce them.
PSE gives you a ready-made benchmark to hold equipment against. For its heat-pump-to-heat-pump upgrade rebate it requires a COP of at least 1.75 at 5°F, and AHRI rated capacity at 5°F of at least 70% of AHRI rated capacity at 47°F. That is a good bar for any Bellingham installation and a necessary one in the foothills, where Glacier’s design temperature is 13°F.
What ruins a good rating after installation
Ratings are laboratory results for correctly installed, correctly charged, correctly sized equipment. Three things in the real world take them apart.
Oversizing. An inverter-driven unit that cannot turn down to your shoulder-season load cycles instead of modulating, and cycling loses the efficiency the rating measured. This is the most common cause of a high-rated system delivering ordinary bills.
Refrigerant charge and airflow. A charge that is off, a restricted filter, or a duct system with more static pressure than the equipment was tested against all move real performance below the label. The M1 test procedure exists precisely because the old one was too generous about static pressure.
A fouled outdoor coil. In our climate, fir needles, moss and salt do measurable damage to heat transfer, and a coil nobody has cleaned in four years is not the equipment you bought. That is why the maintenance schedule is part of the efficiency conversation rather than separate from it.
Questions Bellingham homeowners actually ask
- What is a good HSPF2 for Bellingham?
- Use PSE’s tiers as a practical floor: 8.1 HSPF2 gets you into the lowest midstream tier, 8.5 into the middle and 9.5 into the top tier worth $600 per unit. In a heating-dominated climate the extra HSPF2 is generally worth more than extra SEER2, and the low-ambient capacity table matters more than either.
- Is SEER2 worth paying for here?
- Less than almost anywhere else in the country. Our cooling design temperature is 78°F and climate zone 4C runs 0 to 500 cooling degree days, so the cooling season is short. Buy the heating efficiency and take the cooling efficiency that comes with it.
- Why is my new unit’s SEER2 lower than my old unit’s SEER?
- Because they were measured by different tests. The M1 procedure adopted in 2023 tests at a higher external static pressure than the old procedure, so the same physical equipment scores lower under SEER2 than under SEER. It is not a downgrade in performance, and comparing across the two is meaningless.
- What COP should I expect on a 19°F morning?
- Ask for the manufacturer’s performance table rather than accepting a general answer, because it varies substantially by model. A useful reference point is PSE’s cold-climate threshold for its upgrade rebate: a COP of at least 1.75 at 5°F, well below our 19°F design temperature. Equipment that clears that bar is still moving more heat than it consumes on the coldest morning you are likely to see.
- Does a higher rating mean a bigger rebate?
- Through the PSE midstream equipment discount, yes — $300, $400 or $600 per unit by tier, limited to one unit per residential retrofit project. The $1,500 electric-resistance conversion rebate is not tiered by efficiency; it has its own equipment requirements instead. Whether the two stack is unconfirmed.
Have us apply this to your house
Reading it is one thing. Send us the address, the panel size and what you heat with now, and we will tell you what it means for your project.
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Tell us what you have now and what you want it to do. We will tell you what fits, what it costs, and which rebates you actually qualify for — before anyone comes out.
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