Watch the Pressure Drop, Not the Date
As a filter loads, its pressure drop (ΔP) rises and the fan works harder. The rule: replace when ΔP reaches the manufacturer’s final limit-typically about 2× the initial ΔP-or when energy cost outweighs the filter price.
Typical Service Intervals
| Stage | Initial ΔP | Replace at | Typical life |
|---|---|---|---|
| Primary G3/G4 | 20-45 Pa | ~90-100 Pa | 3-6 months |
| Medium F5-F9 | 45-90 Pa | ~130-180 Pa | 6-12 months |
| HEPA H13/H14 | 100-250 Pa | Per test / 2-3 yr | 1-3 years |
How to Monitor
- Fit a differential pressure gauge or manometer across each bank.
- Log readings monthly; trend the slope to predict changeout.
- Bag collapse, visible discolouration or odour breakthrough are visual cues.
Safe Changeout
- Shut the fan, lock out, and use PPE for contaminated media.
- Disposable media: bag-in/bag-out; never wash-and-reuse synthetics.
- HEPA: after install, run a PAO/DOP leak scan to confirm integrity.
- Log every changeout with date, location and part number.
