ERV / HRV Effectiveness Calculator

Enter the inlet and outlet conditions of the supply air to find the sensible and (with humidity) enthalpy effectiveness of an energy recovery ventilator or HRV.

How effectiveness is defined

Sensible effectiveness = (T_supply,out − T_outdoor) / (T_exhaust − T_outdoor). It only looks at temperature. Enthalpy effectiveness uses the full moist-air enthalpy (temperature + humidity), which is what an ERV — as opposed to a plain HRV — recovers.

Frequently asked questions

ERV or HRV — which number matters?

An HRV only transfers heat, so judge it on sensible effectiveness (typically 70–85%). An ERV also transfers moisture, so the enthalpy figure is the honest one — often 60–80%.

Why is my enthalpy number lower than sensible?

Most wheels/plates transfer heat better than moisture. A gap of 10–20 points is normal; a much larger gap suggests the core is saturated or fouled.

What humidity ratio should I use?

It is the mass of water vapour per mass of dry air (kg/kg). At 50% RH and 22°C, indoor air is about 0.008–0.009 kg/kg. Use our psychrometrics tool to get it from temperature and RH.