Duct mounted filter boxes (filter cassette boxes) for round ventilation ducting. We stock the Systemair FGR and FFR series from 100mm to 400mm, fitted inline to hold a replaceable panel filter that protects fans, heat exchangers and supply air from dust and pollen. FFR boxes come with a BFR-M5 filter included. All genuine Systemair, in UK stock with next working day delivery. Use the buttons below to filter by duct size, or for help choosing the right box or replacement filters email hello@efans.co.uk or call 0161 399 3825.
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Frequently asked questions
What is a duct filter box for?
A filter box sits inline in the ductwork and holds a replaceable filter cassette, cleaning the air passing through. It protects the fan and any downstream heat exchanger or coil from dust build-up and keeps supply air clean, which matters on MVHR, supply and commercial systems.
FGR or FFR, what's the difference?
Both are circular duct mounted filter cassette boxes. The FFR is supplied complete with a BFR-M5 filter ready to run; the FGR is the filter box housing. Choose the size to match your duct diameter, 100mm to 400mm.
Which filter grade and how often do I replace it?
These boxes take BFR panel filters, commonly M5 (medium) grade for general supply and extract; finer grades are available where cleaner air is needed. Replace filters when they discolour or airflow drops, typically every 6 to 12 months depending on the environment. Keep spare BFR filters on hand.
SKU: 1783