EER Calculator

EER: why peak-condition efficiency matters during Canadian heat waves

EER (Energy Efficiency Ratio) measures cooling efficiency at one specific, demanding test condition, typically 35°C outdoor and 26.7°C indoor, rather than the seasonal average that SEER represents. This single-point measurement matters because it tells you how the system performs precisely when you need it most: during a sustained summer heat wave when outdoor temperature stays near or above design conditions for days at a time, and the air conditioner runs at or near full load continuously rather than cycling on and off as it does during milder weather.

Two units with identical SEER2 ratings can have meaningfully different EER values, because SEER2 averages performance across a wide range of conditions weighted toward the more common mild-to-moderate temperatures that make up most of a typical cooling season. A unit optimized to perform exceptionally well at partial load (boosting its SEER2 average) might show comparatively weaker performance at full peak load (a lower EER) than a unit engineered for more consistent performance across the full range. For Canadian climates that experience multi-day summer heat events, like Toronto, Windsor, and southern Manitoba, checking EER alongside SEER2 gives a more complete efficiency picture.

Converting between EER and COP

COP (Coefficient of Performance) is the dimensionless ratio used throughout refrigeration engineering, calculated as useful cooling output divided by energy input, both in the same units. EER, measured in BTU per watt-hour, converts to COP by dividing by 3.412 (since 1 watt-hour equals 3.412 BTU). An EER of 12 corresponds to a COP of approximately 3.52. This conversion is useful when comparing North American EER-rated equipment specifications against COP-rated specifications more commonly used in technical literature or equipment from other regions.

Estimating heat wave cooling cost

Use the peak-load cost mode to estimate the actual electricity cost of running an air conditioner near continuously during an extended heat wave, using the unit's EER rating rather than its seasonal SEER2 average. This gives a more realistic cost estimate for the specific scenario of sustained extreme heat, which is exactly the condition where EER is the more relevant efficiency metric than SEER2. Compare this peak-load cost scenario against your typical seasonal cost from the SEER calculator to understand how much of your annual cooling bill is driven by these extreme events versus typical operation.