Defro DRX / OPTI V filters

Defro is best known as a manufacturer of biomass boilers and fireplaces, but its range also includes the Defro AIR line – residential heat recovery ventilation units, often installed in the same house alongside Defro heating equipment. Defro AIR filters are measured and classified the same way as filters for other manufacturers' MVHR units, so identifying the model from the label on the unit or measuring the filter directly both work equally reliably.

Defro AIR units typically use two-stage filtration, following the industry-standard M5/F7 combination:

• a coarser filter that protects the heat exchanger from dust and debris
• a finer F7-class filter for the supply air stream

When buying filters, it's also worth checking the ISO 16890 class (e.g. ePM10 or ePM1), which today is often listed alongside the older EN 779 designation in the user manual.

The usual recommendation is to check the filters every 3 months and replace them when you notice reduced airflow or increased noise – typically 2–4 times a year, depending on outdoor air pollution and the number of occupants. Buying a year's supply (2–4 sets) at once is a convenient way to make sure you're never caught without a filter at the wrong moment, and buying several sets together usually works out to a lower price per unit than buying one at a time.

Yes, the Defro AIR filter compartment is designed for front or side access, and removing the old filter and fitting a new one usually requires no tools. Simply unscrew the cover or release the latch, pull out the old filter, check its condition, and insert the new one in the same orientation (arrow pointing in the direction of airflow). If you're unsure of the exact steps for your specific model, it's worth checking the manufacturer's user manual – the procedure is similar across all Defro AIR models.

When a Defro AIR unit is installed close to a biomass boiler or fireplace, the outside air intake sometimes picks up a smoky smell. In that case, a supply filter with an activated carbon layer helps absorb some of the volatile smoke particles and odour before the air enters the rooms. This filter is fitted as an additional stage alongside the standard M5/F7 filter set, not in place of it, so the main particle filtration is not compromised.

No. Our catalogue covers the standard Defro AIR filter sizes, so there's no need to order from Poland or wait for the manufacturer's own delivery. In-stock filters are dispatched within 1–2 business days and delivered throughout Estonia via Omniva, SmartPost and DPD; only clearly marked made-to-order items have a longer lead time of 5–10 business days. Check the exact model on the unit's label before ordering, or measure the old filter, so the replacement matches your Defro AIR unit precisely.