Heat Recovery Efficiency Calculator

Work out heat recovery efficiency instantly with clear inputs, formula shown and shareable results.

About Heat Recovery Efficiency Calculator

Sensible effectiveness measures how much of the available temperature difference the exchanger actually transfers: the supply air rise divided by the gap between exhaust and outdoor temperatures. The energy recovered is then the familiar sensible relation 1.08 x CFM x rise.

Formulas

Effectiveness

ε = (supply out - supply in) / (exhaust in - supply in)

Recovered heat

BTU/h = 1.08 x CFM x (supply out - supply in)

Worked example

With the default values below, Heat Recovery Efficiency Calculator returns Sensible effectiveness of 77.1%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Outdoor air enteringminimum -40 °F: 35 °F
Supply air leaving exchangerminimum -40 °F: 62 °F
Exhaust air enteringminimum -40 °F: 70 °F
Airflow through exchangerminimum 1 CFM: 1,000 CFM

Results

Sensible effectiveness: 77.1% %
Temperature recovered: 27.0 °F
Heat recovered: 29,160 BTU/h
Heat recovered in kilowatts: 8.55 kW

Step by step

1Values used
2Effectiveness
3Recovered heat
4Sensible effectiveness= 77.1 %
5Temperature recovered= 27.0 °F
6Heat recovered= 29,160 BTU/h
7Heat recovered in kilowatts= 8.55 kW

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Heat Recovery Efficiency figure worked out?

ε = (supply out - supply in) / (exhaust in - supply in). Sensible effectiveness measures how much of the available temperature difference the exchanger actually transfers: the supply air rise divided by the gap between exhaust and outdoor temperatures.

Does effectiveness include latent recovery?

No. This is the sensible figure only. An enthalpy wheel also moves moisture, and its total effectiveness must be assessed on enthalpy rather than temperature.

What values do I need to enter?

This calculator takes 4 inputs: Outdoor air entering, Supply air leaving exchanger, Exhaust air entering, Airflow through exchanger. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.