EER to SEER Calculator — SEER2, COP & kW/Ton

EER, SEER and SEER2 — what can actually be converted?

The ratings are related, but they are not interchangeable measurements. EER is measured at a specified operating condition. SEER and SEER2 average performance over a prescribed seasonal test procedure. Because equipment can behave very differently at part load, there is no single exact EER-to-SEER or SEER-to-SEER2 multiplier that works for every model.

EER — Energy Efficiency Ratio

EER = cooling output (BTU/hr) ÷ electrical input (watts) at the rating condition. Because both quantities describe the same operating point, EER converts directly to COP and kW/ton.

COP and kW/ton — exact same-condition conversions

COP = EER ÷ 3.412 and kW/ton = 12 ÷ EER. These equations require the ratings to refer to the same cooling operating condition.

SEER and SEER2 — seasonal ratings

SEER is the legacy seasonal cooling-efficiency metric; SEER2 is the current seasonal metric for covered central air-conditioning and heat-pump products under the newer DOE test procedure. A model's published SEER2 should come from its certified rating or specification sheet. Do not back-calculate an exact SEER2 from EER, and do not assume every old SEER value converts to SEER2 with the same percentage.

Why EER-to-SEER conversion formulas are only approximations

It is tempting to treat every efficiency rating as a different unit for the same quantity, but that is not what these labels represent. EER is a point-condition ratio: cooling output divided by electrical input while the equipment is operating at a specified rating condition. SEER and SEER2 are seasonal metrics: they combine performance across a prescribed series of conditions and part-load behavior. Two air conditioners can therefore have the same EER at one operating point and still have different seasonal performance.

This is why a fixed formula such as “SEER = EER × 1.12” can be useful only as a rough historical rule of thumb. It cannot reconstruct how a specific compressor, fan controls, staging strategy or variable-speed system behaves across the seasonal test. DOE guidance likewise notes that conversions between seasonal and point-condition metrics vary with climate and are imprecise. For purchasing, rebates, standards or product comparisons, use the published certified rating instead of a derived value.

When an exact conversion is possible

EER, cooling COP and kW/ton can be converted directly when they describe the same operating point. EER is BTU/hr per watt. Dividing EER by 3.412 converts that ratio to cooling COP because one watt equals approximately 3.412 BTU/hr. Likewise, one ton of cooling is 12,000 BTU/hr, so kW/ton equals 12 divided by EER.

For example, a unit operating at EER 12 has a cooling COP of about 3.52 and requires about 1.00 kW per ton at that same rating condition. Those are unit conversions from the same underlying output/input ratio; they do not require guessing seasonal part-load behavior.

Why SEER2 should be read from the product rating

SEER2 is produced under the newer DOE test procedure for covered central air conditioners and heat pumps. The test procedure changed more than the printed number: it changed the laboratory framework used to calculate seasonal efficiency. That means an old SEER value and a new SEER2 value are best treated as two published test results, not as currencies that always exchange at one fixed rate.

If you are comparing an older system that has only a SEER rating with a new system that has SEER2, look first for certified historical data for the older model or an equivalent manufacturer rating. If that is unavailable, any cross-standard conversion should be labeled as an approximation—not presented as exact compliance or savings math.

How the seasonal cooling-cost estimate works

The savings and running-cost tabs intentionally work only with SEER or SEER2 entered as published. The planning equation is:

Estimated cooling kWh = capacity (BTU/hr) × full-load-equivalent cooling hours ÷ seasonal efficiency rating ÷ 1,000.

The “cooling hours” input is not meant to imply that the compressor runs at full rated capacity for every clock hour of summer. It is a simplified full-load-equivalent-hours input used to translate a seasonal load into a planning estimate. The default choices use DOE generalized climatic-region reference hours; your own energy audit, utility analysis or engineering estimate is better when available.

Example: comparing 15 SEER2 with 20 SEER2

Suppose a 3-ton system (36,000 BTU/hr) is modeled at 1,200 full-load-equivalent cooling hours per year. At 15 SEER2, the simplified estimate is about 2,880 kWh/year. At 20 SEER2, it is about 2,160 kWh/year. At $0.16/kWh, that is roughly $461 versus $346 per year—a planning difference of about $115/year.

The percentage comparison is more useful than pretending those dollars are a guaranteed utility-bill result. Weather, thermostat settings, latent load, duct losses, cycling, installation quality and actual part-load performance can all move real consumption. Use the calculator to compare scenarios, then use certified equipment data and local load information for a purchase decision.

SEER2 is not a peak-power rating

Do not divide a unit's BTU/hr capacity by SEER2 to claim its instantaneous electrical draw at a hot design condition. SEER2 is seasonal. For a point-condition power comparison, use a published EER/EER2 or manufacturer performance table measured at the relevant condition. This distinction is why the revised calculator no longer manufactures a “peak kW” value from SEER2.

How to check current SEER2 and ENERGY STAR requirements

Federal efficiency requirements are not a single universal SEER2 number for every air conditioner. The applicable requirement depends on the product type, capacity and—in some cases—region. Window and portable room air conditioners also use different efficiency metrics from central split systems.

For a purchase or compliance decision, identify the exact product category and check the current DOE requirements or the model's certified rating. ENERGY STAR criteria are higher than federal minimums and also vary by product category. For example, ENERGY STAR's current split-system air-source heat-pump criteria include separate SEER2, EER2 and HSPF2 thresholds rather than one all-purpose efficiency grade.

Official references: DOE central AC / heat pump standards · ENERGY STAR heat-pump criteria.

What SEER2 rating should you buy?

There is no universal "best" SEER2. A higher seasonal rating can reduce cooling electricity use, but the value of the upgrade depends on your cooling load, full-load-equivalent operating hours, electricity price, installed-cost premium and equipment sizing.

Use the Old vs new savings tab with the published seasonal ratings for the two systems you are comparing. The calculator's default cooling hours come from DOE generalized climatic regions and are only a planning input; replace them with a better local or household estimate when you have one.

For equipment sizing first, use the AC size calculator. For a detailed home load, use the BTU calculator or a professional Manual J calculation.

How to get more value from a higher efficiency rating