Filters

Frequently asked questions

How often should I change my ventilation filters?

As a rule, replace MVHR and heat recovery filters every 6 to 12 months, and check them every 3 months. Homes near busy roads, building sites or with high pollen exposure clog faster and may need changing twice a year. A blocked filter forces the fan to work harder, raises running noise and energy use, and cuts airflow, so a low-cost filter change is the cheapest way to keep a system performing. Most units have a filter-change indicator or a service interval in the manual.

What do the filter grades G3, G4, M5 and F7 mean?

They describe how fine a particle the filter captures. Coarse grades G3 and G4 (ISO Coarse) stop insects, leaves and larger dust, and are used on PIV units and as the first stage on many MVHR units. M5 (ISO ePM10) catches finer dust and some pollen. F7 (ISO ePM1 55%) is the pollen and fine-particle grade recommended for the supply side of MVHR in homes with allergy or air-quality concerns. Many MVHR units run a coarser filter on extract and a finer F7 grade on supply.

Which filter does my unit need?

Match the filter to your exact unit model, not just the brand. Our listings name the compatible unit and filter set, for example a Systemair or Villavent VR 400, or a Vent-Axia PoziDry Compact 479188. If your model is not obvious, check the label inside the unit door or the original manual, or call us and we will identify the right set. You can also use our Filter Finder tool to confirm the unit.

Do I need to replace both the supply and extract filters?

Yes. MVHR units have two filters, one on the incoming fresh air and one on the outgoing stale air, and both should be changed together so airflow stays balanced. Most of our replacement sets are supplied as a matched pair for this reason. Running one new and one clogged filter unbalances the heat exchanger and reduces efficiency.

What grade filter does a PIV unit use?

Positive input ventilation units such as the Vent-Axia PoziDry draw air from the loft or outside and push it into the home, so they use a coarse G3 or G4 filter to catch loft dust, insects and pollen. These are inexpensive and should be checked yearly, as a loft environment can clog them faster than you would expect.

Can I wash and reuse ventilation filters?

Generally no. Pleated MVHR and pocket filters use fine synthetic media that is damaged by washing, which destroys their rating and lets particles straight through, so they should be replaced. Some coarse metal or plastic-mesh panel guards can be vacuumed or rinsed, but the filter cartridges are consumables. Replacing rather than washing keeps the manufacturer's airflow and efficiency figures valid.