heat recovery ventilation

A heat recovery ventilation system is a method of saving the energy normally lost through ventilation, when outside air is cooler or warmer than the desired inside temperature. This is done by installing a counter-flow heat exchanger at the point or points where fresh air from outside is let into a building.

The counter-flow exchanger transfers heat between ventilation air streams. It reduces losses when incoming air differs in temperature from the desired indoor conditions.

The definition retains the counter-flow exchanger arrangement. Ordinary ventilation without that heat-recovery function does not establish the feature.