How Frost Forms

In cold weather the warm exhaust air cools as it gives up heat. If its dewpoint is above 0 C, water condenses; if the surface drops below 0 C, that condensate freezes into frost on the exhaust side.

Why It Matters

Frost narrows the channels, raises pressure drop, and eventually blocks the core, collapsing effectiveness and stressing the fan.

Mitigation Methods

• Timed bypass or recirculation defrost
• Preheat of incoming air
• Frost-resistant core geometry

Design Note

Set the defrost strategy from the coldest expected outdoor temperature, not the annual average, or the core will ice up during the worst week of the year.