AHU filters: when to change them and why not to trust the calendar

What filters are for

Filters in an air handling unit protect both the air supplied to the building and the unit's own coils from dust. Without them dust sticks to the cooling coil, heat exchange worsens and the drain pan becomes a breeding ground for bacteria.

Managing by pressure drop

Pressure is measured before and after each filter stage. The resistance of a clean filter is listed in the manufacturer's catalogue; the final resistance is usually two to three times higher. When that limit is reached, the filter is changed.

Installing a differential pressure gauge or a BMS sensor takes the guesswork out of this decision.

Practical intervals in Baku

In our experience, pre-filters in windy areas or near construction are changed every 1–2 months and fine filters every 3–6 months. In hospitals and laboratories HEPA filters follow their own schedule with leak testing.

The hidden cost of a clogged filter

As a filter clogs, the fan works harder to deliver the same air volume. In units with a frequency drive that means higher electricity use; in units without one, less air reaches the rooms.