How often should you clean your HRV / air exchanger filters?

Clogged HRV filters cut fresh-air flow and make the system work harder.

Blocked filters unbalance the supply and exhaust flows, which is worse than it sounds. An unbalanced ventilator can pressurise or depressurise the house, driving moist air into wall cavities or pulling combustion gases back down a flue. Efficiency drops too, but the pressure imbalance is the real problem.

1. Switch the unit off at its own control. Do not rely on a wall switch alone. Use the unit’s power switch or its breaker.
2. Open the front cover. Usually two clips or thumbscrews. The unit is typically in a basement, loft or laundry.
3. Withdraw both filters. There are two, one on the supply side and one on the exhaust. People routinely clean only one of them.
4. Wash or replace as specified. Many are washable: rinse, shake, and dry completely before refitting. A damp filter grows mould.
5. Pull and rinse the core. Once or twice a year the aluminium or plastic core itself should come out and be washed in mild soapy water.
6. Clear the exterior hoods. The intake and exhaust grilles outside collect leaves, insects and lint.

• Windows fogging on the inside in cold weather when they did not before
• Stale or stuffy air despite the unit running
• The unit noticeably louder as the fans work against the restriction
• Visible dust matting the filter media

• Cleaning one filter and not the other
• Refitting filters while they are still damp
• Never removing the core, which is where the real fouling accumulates
• Forgetting the outdoor intake hood, which is often the actual blockage

• Pollen season loads the supply filter quickly
• Nearby construction or a busy road shortens the interval
• Cooking-heavy households load the exhaust side faster

If supply and exhaust flows need rebalancing, that requires a technician with a flow hood. Filters and core cleaning are firmly a homeowner job.