Baffle, mesh or charcoal: which chimney filter needs what care

Most chimney trouble starts at the filter, and most filter trouble starts with treating one type like another. There are three you will meet, and they want different things.

Baffle filters

Stacked steel plates that force air through a zigzag, dropping oil into a tray. Standard on almost every chimney sold in the last decade. They are tough and washable: a soak in hot water with degreaser, a soft brush, a rinse, dried before refitting. They should last the life of the chimney.

Mesh filters

Layers of fine aluminium mesh, common on older and cheaper units. They clog faster than baffles and are more delicate — scrubbing hard tears the mesh and then oil goes straight through to the fan. Wash gently and often, and expect to replace them every couple of years.

Charcoal filters

Found only in ductless chimneys, sitting behind the main filter to absorb smell before air is recirculated. These cannot be washed. Once saturated they stop working and simply have to be swapped, usually every three to six months. A ductless chimney that has started to smell almost always has a spent charcoal filter.

Never put an aluminium mesh filter in a dishwasher with strong detergent — it blackens and pits. Baffle filters usually survive it; check the manual.

Which do you have?

Pull one out. Rigid plates with a zigzag edge are baffle. A flexible sheet you can flex slightly is mesh. A dark, slightly powdery panel behind either of those is charcoal. If you are not sure, a technician will tell you in a second — and tell you honestly whether it needs cleaning or replacing.