SEER is the seasonal cooling output of an air conditioner divided by the electricity it uses to produce it — higher means less power for the same cooling. Since 2023 the rating on new equipment is SEER2, measured under a tougher airflow test, which is why the numbers read lower than the SEER figures on the unit you are replacing. In Ontario, where the cooling season is short, the practical question is not how high you can go but where the extra money stops earning anything back.
What the SEER number actually measures
SEER stands for Seasonal Energy Efficiency Ratio. It takes the total cooling a system delivers over a simulated season, in BTU, and divides it by the watt-hours consumed to deliver it. Because it is a seasonal average, it accounts for the mild days as well as the hot ones — a unit spends most of the summer at part load, not at full tilt.
The most useful mental model is fuel economy. A higher number means fewer kilowatt-hours for the same cooling, in the same way a higher rating on a car means less fuel for the same distance. And in the same way, the rating is measured on a test cycle that will never exactly match your driving.
SEER2 replaced SEER, and the numbers moved down
The rating system changed in 2023. SEER2 tests the same equipment against a much higher external static pressure — closer to the resistance a real duct system puts in front of a blower than the almost frictionless conditions the old test used.
Nothing about the hardware got worse. The test got more honest, and as a result a given model's SEER2 figure lands several percent below the SEER figure it used to advertise. When you compare a quote to the label on a 2009 condenser, you are comparing two different tests, so do not read the drop as a downgrade. Our companion guide on what SEER2 rating you need in Ontario puts the two scales side by side.
EER2, HSPF2 and the rest of the label
- SEER2 — seasonal cooling efficiency across a simulated summer; the headline number on any air conditioner
- EER2 — efficiency at a single hot design point rather than an average, which is the number that describes how the unit behaves on the worst afternoon of the year
- HSPF2 — the heating equivalent, and only relevant if the outdoor unit is a heat pump rather than a cooling-only condenser
- Capacity in BTU/h or tons — a completely separate specification from efficiency, and the one that determines whether the house gets cool at all
- ENERGY STAR certification — for a split central air conditioner this starts at 15.2 SEER2 together with 12.0 EER2, so a unit has to clear both bars, not just the seasonal one
That EER2 requirement is the part worth understanding in the GTA. Our summers are short but they contain a handful of genuinely hot, humid days, and a system with a strong seasonal average but weak single-point performance is the one that struggles precisely when you notice.
The rating belongs to a matched system, not to the outdoor unit
This is the detail that costs homeowners the efficiency they paid for. A published SEER2 figure applies to a specific combination: that outdoor unit, that indoor coil, and that blower. Change the coil and the combination has a different rating, sometimes markedly lower.
Every certified combination has an AHRI reference number. Ask for it on the quote, and check that the coil model on the quote is the one the number covers. If a contractor proposes a high-efficiency condenser on top of the coil that is already there, the rating on the brochure is not the rating you are buying — and on a system moving to a new refrigerant, that pairing is not permitted at all.
Free quotes, written pricing.
What a higher tier is worth in an Ontario summer
Ontario's cooling season runs roughly from mid-June to early September, and only a fraction of those days demand full output. A high-efficiency air conditioner has fewer running hours here to earn its premium back than the identical unit would have in a southern climate, which stretches the payback on the top tiers considerably.
- Entry tier — lowest price, single-stage compressor, one output level, and the shortest payback if you are selling within a few years
- ENERGY STAR tier at 15.2 SEER2 and above — the band most GTA replacements land in, and the band rebate programs generally recognise
- High tier with a two-stage compressor — meaningfully better humidity control, longer run times, quieter operation, and a defensible premium if you are staying put
- Top tier with a variable-capacity inverter — the best comfort available and the longest payback in this climate; buy it for how it runs, not for the electricity bill
- Any tier — a correctly sized unit installed on a properly sealed duct system will beat a higher-rated unit installed badly, every summer
Where the higher tiers actually earn their money
It is humidity, not kilowatt-hours. A two-stage or variable-capacity system spends most of the season running at reduced output for long stretches, and long run times are what pull moisture out of the air. A single-stage unit reaches setpoint quickly and stops, which leaves the house cool and damp.
That is the comfort difference people describe after an upgrade, and they usually attribute it to the efficiency number. If your current system cools adequately but the air feels heavy, the fix is longer run times rather than more capacity — the mechanism is set out in why a house stays humid with the AC on.
Rebates and where the money goes now
Ontario's incentives have largely moved away from cooling-only equipment and toward heat pumps, which heat as well as cool. The live program is the Home Renovation Savings Program from Enbridge Gas and Save on Energy, launched in January 2025; the qualifying equipment list and amounts change, so read the program page rather than a sales sheet. We keep a current summary on the Ontario rebates page and file the paperwork as part of the install.
Two things you may still see quoted are gone: the Canada Greener Homes Grant is closed to new applicants and Enbridge's Home Efficiency Rebate has ended. If a quote's price depends on either, ask for it again without them.
The verdict: which tier to buy
- Staying under five years, or fitting out a rental — buy the entry tier, size it properly, and spend the difference on duct sealing
- Staying long term in a house that gets humid — buy two-stage at the ENERGY STAR tier or above, because the comfort gain is real and immediate
- Considering heating as well — price a heat pump instead, because that is where the current rebates and the running-cost case both point
- Comparing two quotes — compare the AHRI-matched combinations, not the condenser model numbers
- In every case — the installation, the sizing and the ductwork will beat the rating on the box
ZK Mechanical quotes air conditioning installations across the GTA and Hamilton with the matched combination named on the quote and written pricing before the work starts. The installed ranges by tier are in our GTA AC installation cost guide, and if you would rather have someone read the label on your existing unit before you shop, book a visit.
Frequently asked questions
What is a good SEER2 rating for Ontario?
For most GTA homes the sensible landing zone is the ENERGY STAR band, which for a split central air conditioner begins at 15.2 SEER2 with 12.0 EER2. Below that you save on the purchase and give up the comfort of longer run cycles. Far above it, the short Ontario cooling season means the extra premium takes a long time to return, so buy the top tier for how quietly and steadily it runs rather than for the hydro bill.
What is the difference between SEER and SEER2?
SEER2 is the current rating and it replaced SEER in 2023. The equipment did not change; the test did. SEER2 measures the same system against a much higher external static pressure, which is far closer to what a real duct system puts in front of a blower. The result is that a model's SEER2 figure reads several percent lower than the SEER figure it used to carry, so the two scales cannot be compared directly.
Does a higher SEER2 air conditioner cool better?
No — efficiency and capacity are separate specifications. A correctly sized unit at the entry tier cools a house exactly as far as a top-tier unit of the same tonnage. What higher tiers add is a two-stage or variable-capacity compressor and a variable-speed blower, which run longer at lower output. That removes far more humidity and evens out the temperature between floors, which people experience as better cooling.
Are there rebates for high-efficiency air conditioners in Ontario?
Ontario's incentives now follow heat pumps rather than cooling-only equipment. The Home Renovation Savings Program, run by Enbridge Gas with Save on Energy since January 2025, is the live program, and the qualifying list and amounts are published on the program page — check there rather than relying on a figure in a quote. Neither of the older incentives applies any more — new applications to the Canada Greener Homes Grant ended in 2024, and Enbridge's Home Efficiency Rebate has wound up.
Do I need to replace my indoor coil to get the rated efficiency?
Usually yes. Efficiency ratings are published for matched combinations of outdoor unit, indoor coil and blower, each with its own AHRI reference number. Pairing a new high-efficiency condenser with an existing coil produces a different, generally lower rating — and where the new equipment uses a different refrigerant from the old coil, the pairing is not something a licensed installer can do at all.