Why Ventilation Wastes Energy
Buildings need fresh air, but exhausting conditioned indoor air and bringing in untreated outdoor air can waste a large share of heating and cooling energy. In cold weather the incoming air must be heated; in hot weather it must be cooled. Air-to-air heat recovery closes that gap.
How Air-to-Air Recovery Works
An air-to-air heat exchanger transfers energy between the outgoing exhaust stream and the incoming supply stream without mixing the two airstreams. Sensible recovery moves heat only; enthalpy, or total, recovery also moves moisture, which is valuable in humid climates.
Two Common Designs
- Plate exchangers: stationary aluminium or polymer cores, simple and reliable, good when the two streams must stay fully separated.
- Rotary wheels: a spinning desiccant-coated wheel that stores and releases heat and moisture; high efficiency but with some cross-leakage between streams.
Where It Pays Off
Recovery is most valuable in buildings with high air-change rates: schools, offices, hospitals, and labs. In cold climates, recovering heat from exhaust can cut heating demand by a third or more.
Sizing and Control Tips
- Match effectiveness to climate: higher in cold regions, balanced against fan energy.
- Use bypass dampers in shoulder seasons so free cooling is not blocked.
- Specify frost protection, such as preheat or exhaust recirculation, for very cold sites.
- Keep filters clean; fouling is the main cause of lost performance.
Bottom Line
For most ventilated buildings, air-to-air recovery is one of the shortest-payback energy upgrades available. The hardware is mature, maintenance is low, and the savings recur every heating and cooling season.