Defro DRX / OPTI V filters

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.

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. 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 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. 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.

Considerably, and in a way the calendar won't tell you. During an inversion the cold air sits trapped in the valley floor and the smoke from wood and pellet heating stays at ground level rather than dispersing, so for days at a time the outdoor air carries far more fine particulate than the annual average suggests. That load falls almost entirely on the outdoor-air filter. Through the heating season, check the Defro filters monthly rather than waiting for the scheduled date, and expect to reach the shorter end of your usual interval. The activated carbon set (M5+M5 AC) helps with the smell of smoke, but the particles are still captured by the M5 filters — so it does not change the need for more frequent checks.