Defro DRX / OPTI V filters

Defro is best known for biomass boilers, but it also makes residential ventilation units with heat recovery, often installed alongside Defro heating equipment. We stock filter sets for the Defro DRX V and OPTI V units, which share the same filter size.

Yes — ordering a full year's worth of Defro filters (typically two to four sets, depending on your replacement interval) in one purchase is a convenient way to avoid running low, and multi-set orders are usually priced lower per filter than buying one set at a time.

Yes. The filters in Defro DRX V and OPTI V units sit behind the filter cover and slide out without tools, so you can change them yourself in a few minutes. Switch the unit off before opening the cover and check the airflow arrows on the new filters before inserting them.

Defro DRX V and OPTI V units use an M5+M5 filter set — one M5 filter on the extract side to protect the heat exchanger and one on the supply side. We stock it as an original set and as a lower-cost house brand set, plus an original set with an activated carbon filter for odour control.

Yes. We stock an original Defro DRX V / OPTI V activated carbon set (M5+M5 AC). The carbon layer helps absorb smoke and other odours drawn into the fresh-air intake — for example from a nearby wood burner or biomass boiler — while still filtering dust at M5 level. It replaces the standard set and fits in the same two slots.

It affects the supply side more than most people expect. A great many Finnish detached houses have a masonry heater or a wood stove as backup or supplementary heating, and in a neighbourhood where several houses burn wood the outdoor air carries noticeably more fine soot through the winter — not only from your own chimney. That soot loads the M5 supply filter in DRX V and OPTI V units, so check the filters more often between October and March and change them as soon as they have darkened. If the smell of smoke is the problem, the original M5+M5 activated carbon set absorbs odours while still filtering dust at M5 level; it replaces the standard set rather than being added to it.