A heat recovery ventilator (HRV) helps maintain good indoor air quality by exhausting stale inside air while drawing in fresh outside air. HRVs help control relative humidity, preventing moisture buildup on windows and reducing the chances of mold (a HEPA filter can be added to remove dust and pollens). As the two airstreams—indoor and outdoor—pass through a heat-exchanging core, most of the inside air’s heat is transferred to the incoming air. Even at an outdoor air temperature of 32°F, the Janssens’ Bryant HRV can exchange 211 cubic feet per minute with 69% to 77% percent of the heat transferred back to the incoming air.

Typically, inside air to the exchanger is pulled out of high-moisture areas like baths and kitchens, while fresh air is supplied to bedrooms, assuring whole-house circulation. Although most HRVs are programmed to run intermittently at low speed, a high-speed override can provide on-demand venting when moisture levels are high.

A straightforward installation costs about $3,000, but the recovery of 70% or more of the heat otherwise lost through an exhaust-only system can offer significant savings, especially when extreme differences exist between indoor and outdoor temperatures.

Alternatives to HRVs include exhaust-only ventilation systems, which use standard exhaust fans and a dampered makeup air supply. They are less expensive and consume less energy, but require the homeowner to monitor conditions and adjust the system’s timer accordingly. They also will not maintain a preset humidity and will not recover the heat lost when venting directly to the outside.