Energy Efficiency Ratio (EER)

Also known as EER

\mathrm{EER} = \frac{\dot{Q}\ [\text{BTU/hr}]}{\dot{W}\ [\text{W}]}

Worked example: 36,000 BTU/hr on 3000 W → EER 12 — press Try an example to run it live, then adjust anything.

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Energy Efficiency Ratio (EER) explained

EER is the one HVAC efficiency figure that is proudly dimensional: BTU per hour of cooling divided by watts of electricity. Because 1 W = 3.412 BTU/hr, EER is just COP multiplied by 3.412 — an EER of 12 is a COP of 3.52. It is measured at a single rating point (95 °F outdoor, 80 °F/67 °F entering air), which makes it a peak-day number, useful in Phoenix and slightly beside the point in Seattle. That is why SEER exists: a season-weighted average that includes mild-day part-load operation and always reads higher than EER for the same machine.

The trap is comparing an EER to a SEER, or either to an IEER, as if they were the same currency; a unit advertised at SEER 16 may test at EER 12.5. Worked example: a rooftop unit delivering 36,000 BTU/hr while drawing 3,000 W has EER = 36,000/3,000 = 12.0. Note that this page accepts capacity in kW and returns the same EER, because the 3.412 is baked into the arithmetic rather than into your unit choice.

Energy Efficiency Ratio (EER) formula

\mathrm{EER} = \frac{\dot{Q}\ [\text{BTU/hr}]}{\dot{W}\ [\text{W}]}

Where

$\mathrm{EER}$ = Energy efficiency ratio (BTU/(h·W))
$\dot{Q}$ = Cooling capacity (BTU/h)
$\dot{W}$ = Power input (W)

Missing one of these? Work it out first, then come back

Energy efficiency ratio — EER to COP Conversion, Energy Ratio Between Two Magnitudes
Cooling capacity — Tons of Refrigeration from BTU/hr, Chiller Efficiency (kW per Ton)
Power input — Coefficient of Performance (COP), Chiller Efficiency (kW per Ton)

Part of this formula set

Refrigeration capacity and efficiency

6 formulasTons, COP, EER and kW per ton — the four ways the trade states the same chiller performance, and how to convert between them.