How to check heat recovery ventilator effectiveness
An energy or heat recovery ventilator moves heat from the air you are throwing away into the fresh air you are bringing in. Three temperature readings tell you how well it works. Enter outdoor air, return air, and the supply air leaving the core, and the tool applies effectiveness = (SA - OA) / (RA - OA) x 100, the sensible temperature effectiveness defined in AHRI Standard 1060 and ASHRAE Standard 84.
Recovered heat uses the familiar sensible relation BTU/hr = 1.08 x CFM x temperature difference. With outdoor air at 35°F, return air at 72°F, supply at 62°F, and 300 CFM, effectiveness is about 73%, recovery is roughly 8,700 BTU/hr, and only about 3,200 BTU/hr of ventilation load is left for the heating coil to pick up.
Rated effectiveness is measured at rated airflow and balanced supply and exhaust, so field numbers usually come out lower. Dirty filters, unbalanced airflow, and leaking bypass dampers are the usual culprits. In cold climates the exhaust side can frost when outdoor air drops near or below freezing, which calls for a preheat coil or defrost control. Total energy cores also transfer moisture, so actual utility savings can exceed what this sensible-only number suggests.
Frequently Asked Questions
An HRV transfers sensible heat only, while an ERV core also moves moisture between the two airstreams. ERVs usually win in humid summer climates because they cut latent cooling load as well.
Check filter loading, make sure supply and exhaust airflows are balanced, and confirm the bypass or economizer damper is fully closed. Any of the three will drop measured effectiveness well below the certified value.