What Does EER Mean? And Why Geothermal Is Not Rated in SEER2
EER means Energy Efficiency Ratio: cooling BTUs delivered per watt-hour of
electricity, measured at one steady condition. Geothermal heat pumps are rated in EER and COP, not
SEER2 and HSPF2, because a ground loop feeds them steady water instead of swinging Oklahoma air.
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This is the acronym that trips up the most homeowners, because the numbers on a geothermal sheet
look nothing like the numbers on the air conditioner quote sitting next to it, and people assume
somebody is hiding something. Nobody is. They are different measurements.
EER is a snapshot. SEER2 is a season.
EER is measured at one fixed set of conditions. It answers a narrow question: right now, at this
condition, how much cooling do I get per watt? For a geothermal system that is exactly the right
question, because the loop holds conditions steady. The snapshot is basically the whole movie.
SEER2 and HSPF2 exist because an air-source system’s performance swings all over the place across a
season. Those ratings average the swing. That is honest and useful for air-source equipment, and it is
meaningless for a machine sitting in 60-something degree loop water in both July and January.
| Rating | What it measures | Applies to | Higher is |
|---|---|---|---|
| EER | Cooling BTUs per watt-hour at one steady condition | Geothermal, water source | Better |
| COP | Heat moved per unit of electricity in | Geothermal, water source | Better |
| SEER2 | Cooling efficiency averaged over a season of outdoor air | AC, air-source heat pumps | Better |
| HSPF2 | Heating efficiency averaged over a season of outdoor air | Air-source heat pumps | Better |
Do not compare an EER to a SEER2 and decide one system won. They are not the same units and they are
not measured the same way. It is like comparing a truck’s towing capacity to its top speed.
What EER does to your wallet
The dollar version
EER is the cooling side of the same story COP tells on the heating side. Put together, a geothermal
system cuts the energy your heating and cooling uses by roughly half compared with the conventional or
propane system it replaced. Energy use, not the whole bill.
Here is the part that matters in an Oklahoma July. An air conditioner’s real-world efficiency sags
on a 104 degree afternoon, because it is trying to dump heat into air that is already hot. A geothermal
system is dumping that heat into ground that has not noticed the heat wave. It holds its rating on the
worst day of the year, which is the day your bill is being written.
The one number that quietly wrecks a good EER
Static pressure. A high-EER unit choked by undersized or leaky ductwork cannot deliver what it is
rated for, and the blower burns extra watts fighting the duct system all day. I check it on every job.
It is the least glamorous measurement in this trade and it costs people real money.
Same story on the water side. EER is published at a stated entering water temperature. If the loop
is short, the water comes back further from ideal, and the number you actually get is not the number on
the sticker. Loop design is not paperwork, it is the rating.
What ratings I look at when I spec a unit
Full-load EER and part-load EER, the COP at the entering water temperature your loop will really
produce, and whether it is a single stage, two stage, or variable speed compressor. A variable speed
unit spends most of its life at part load, so the part-load number is the one you live with. A lot of
quotes only show you the flattering one.
I install ClimateMaster as my main geothermal line and I am a GeoElite dealer, so I will happily walk
you through the actual AHRI data for the exact model I am proposing rather than a marketing range. See
ClimateMaster geothermal in Oklahoma.
No video on this one on purpose. The obvious candidate on my channel is the
ClimateMaster Trilogy 45 walkthrough, and its description carries two lines I no longer stand behind.
It goes back up when the description is fixed.
Questions I get about this
What is a good EER for a geothermal heat pump?
Modern geothermal units post EER numbers well above what an air conditioner can reach, because they reject heat into ground instead of hot air. What matters more than the headline number is the EER at the entering water temperature your loop will actually deliver, and that comes down to loop design.
Does geothermal have a SEER rating?
Not a meaningful one. SEER2 averages performance across a season of outdoor air temperatures, and a geothermal unit does not see outdoor air. It sees loop water. So it is rated in EER and COP. Anyone quoting you a SEER2 figure for a geothermal system is using the wrong sheet.
What does HSPF mean, and does it apply here?
HSPF and its current version HSPF2 are the heating-season rating for air-source heat pumps. Geothermal uses COP instead, for the same reason it uses EER instead of SEER2. If you want the heating side, read what COP means.
Is a higher EER always worth paying for?
Not automatically. Past a point you are paying for a number you will not recover on an Oklahoma utility rate, and that money is often better spent on the loop or on fixing the ductwork. I will tell you where that line is for your house instead of selling you up to the top of the catalog.
How much does a geothermal system cost in Oklahoma?
New system estimates are free anywhere in Oklahoma, and I would rather look at the house than guess. Ranges, loop cost factors, and the verified utility rebates are on my geothermal cost page.
Keep going:
Want to see the real rating sheet for your house?
I will pull the AHRI data on the exact model I am proposing, at the entering water temperature your loop will really produce, and show you the part-load number too. Free estimate, statewide, no pressure.
Dave Hartzell, Hartzell's Heat & Air, 602 S Main St, Kingfisher, Oklahoma. Master HVAC License, NATE Certified, IGSHPA Accredited, ClimateMaster GeoElite. New system estimates are free anywhere in Oklahoma. Diagnosing an existing geothermal system is my $348 flat Geothermal Diagnostic, no credit and no refund, with a written report before I leave.