1. When an air handling system is designed, the preheat coil is often given a large surface margin. In winter, because the surface greatly exceeds the duty, operators reduce the heat medium flow too far and the coil freezes and splits.

2. Poor installation or piping leaves water at the lowest point of the exchanger. During winter operation that water freezes and cracks the coil.

3. In systems that supply warm air only in winter, operators again cut the heat medium flow to save energy and the coil freezes.

4. If the heat source is shut down while the supply fan keeps running, water remaining in the exchanger is exposed to cold outdoor air and freezes.

5. With steam as the heat medium, a failed steam trap — either not draining or not holding back steam — allows condensate to accumulate; the standing water freezes and splits the exchanger.

6. In systems shut down for the winter, internal leakage through a valve or water left in the exchanger will freeze when the fresh-air damper is open and cold air enters.

7. Where a system has both a heater and a cooler and the cooler is installed upstream of the heater, cold outdoor air passes through the cooler first in winter. Any water left in the cooler coil freezes and damages it.