Why Defrost
When exhaust air drops below freezing, frost forms on the core and blocks it. Several strategies exist; pick by climate and device.
Strategies
| Strategy | How | Best for |
|---|---|---|
| Preheat coil | Warm intake above frost point | Plate and most cores |
| Defrost bypass | Periodic warm-air purge | Plate, rotary |
| Recirculation | Mix return air into intake | Cold climates |
| Purge sector | Wheel sector clears frost | Rotary wheels |
| Frost-resistant core | Wider channels, hydrophobic surface | All, milder frost |
Selection Note
Set the strategy from the coldest expected outdoor temperature, not the annual average, or the core ices up during the worst week.