Cooker hood grease filter vs carbon filter: which to clean, which to replace

Your cooker hood starts pulling more weakly, cooking smells linger around the kitchen, and grease builds up faster on the cabinets above the stove — almost every time, the culprit is a clogged filter. The grease filter and the carbon filter in a cooker hood are two completely different parts: one you wash, the other you only replace, and mixing them up means either wasting money or quietly killing the motor without noticing. This is an honest read from the bench — which filter to clean and how often, which one must never be washed, how a recirculating hood differs from a ducted one, and when a clean filter saves the appliance from the service centre.

Two kinds of filter: the metal grease filter and the carbon filter

The biggest mistake we see is people treating both filters as one and the same thing. They do completely different jobs and they are maintained in completely different ways.

The metal grease filter is the one you see when you look up under the hood — an aluminium or stainless-steel mesh with several layers of fine screen, usually held by a spring catch or a ring. It catches the grease aerosol and solid particles from the steam before they reach the fan. The grease filter is washable and lasts the whole life of the hood — you do not replace it, you clean it.

The carbon (activated-charcoal) filter is a different animal. It is a thicker cartridge filled with activated-charcoal granules or a charcoal-impregnated pad, usually clicked onto the fan housing on the inside of the hood. Its job is not to catch grease but to adsorb odours — to bind the smell molecules when the hood does not vent air outside but cleans it and returns it to the kitchen. The carbon filter is a consumable: you do not wash it, you replace it.

The simple principle that holds for almost every model:

If your hood vents air outside through a duct, it most likely has no carbon filter at all and does not need one — more on that below.

How to wash the grease filter so suction doesn't drop

The grease filter clogs gradually, and that is exactly why people often fail to notice the suction slowly fading — until the moment the kitchen starts to smell. The accumulated grease layer blocks the mesh holes, the airflow drops, and the motor runs against resistance. With active use it is worth washing the filter every 3–4 weeks, or every two weeks if you cook a lot with deep frying.

The safest way is in the dishwasher or by hand in hot water. Step by step:

1. Switch the hood off and unplug the lighting if you are also changing a bulb. You do not need power to remove the filter, but hot water and slippery metal mean the area should be safe.
2. Take out the metal filters. Pull the spring catch or turn the ring — the filter drops into your hand. On most hoods you can do this without a tool.
3. Soak in hot water with dish soap for 10–15 minutes so the grease softens. For stale, smelly filters add a spoonful of baking soda — it breaks down the baked-on grease.
4. Brush with a soft brush in both directions to clear the mesh holes. Do not use metal brushes or abrasives — they scratch the aluminium and open it up to oxidation.
5. Rinse thoroughly and dry completely before refitting. A wet filter sitting on the fan is an invitation to corrosion and an unpleasant smell.

One technical note: aluminium filters in a dishwasher with aggressive salt and high temperature go grey and matte over time. That is purely cosmetic and does not affect suction — the filter works just as well. If you want to keep the shine, wash it by hand.

If suction still hasn't recovered after a clean filter, the problem is deeper — we cover that in Cooker hood weak suction.

Why the carbon filter must never be washed, only replaced

This is the point where people go wrong most often and then wonder why the kitchen still smells. Activated charcoal binds odours through adsorption: the micropores in the granules fill up with smell molecules until there is no free space left. Once the charcoal is saturated, it simply stops working — and you cannot restore it by washing. Water does not rinse the pores clean; instead it washes the charcoal dust out of the cartridge, ruins the pad, and leaves a wet, musty material that only makes the air worse.

Practical rules for the carbon filter:

• Replacement interval — roughly every 3–6 months depending on how often you cook. With heavy use, closer to three months.
• The sign that it's time to change — odours come back even though the grease filter is clean. That means the charcoal is saturated.
• Washing doesn't help and does harm — even if the packaging says "regenerable," that usually means only brief drying, not washing in water.
• Check whether you even have one. Ducted hoods have no carbon filter.

A carbon filter is a small cost compared with what stale air and the indirect load on the motor cost in the long run. Replacing it is a consumable expense, not a repair.

Recirculating vs ducted — why it decides which filter you use

Whether you need a carbon filter at all depends on how the hood works. There are two modes, and many hoods can do both — the difference is in the installation.

Ducted mode drives the polluted air out of the room through a duct — into a ventilation shaft or through the wall to the outside. Smells, steam, and moisture leave the kitchen, so a carbon filter is not needed here. Only the metal grease filter works. This is the most effective mode, both for suction and for fresh air.

Recirculating mode sends no duct outside. The air passes through the grease filter, then through the carbon filter to clean the odours, and returns to the kitchen. It is used when there is no external outlet — in many Riga flats the ventilation shaft is shared and you are not allowed to force steam into it with a fan. In exactly this mode the carbon filter is mandatory and must be replaced regularly.

The practical takeaway: if you have recirculation and odours persist, replace the carbon filter first — don't tear the hood off the wall. And if you are planning to change the hood, first find out whether the building even has room for a duct — that decides whether you get a fresh-air kitchen or a lifetime of carbon-filter changes.

How a clogged filter affects the motor and noise

A clogged filter is not just a cosmetic matter — it directly harms the appliance, and this is exactly where a maintenance problem grows into a service job.

When the grease holes are blocked, the fan pulls against resistance. The consequences we see on the bench, in order of frequency:

• Noise and vibration rise. The grease layer on the fan blades does not settle evenly — the rotor goes out of balance, the bearings start to hum and rattle. This is the most common cause of "my hood has got loud."
• The motor heats and runs at its limit. A shaded-pole motor under high load draws more current for longer; the windings heat up, and the thermal protection (if there is any) tends to cut the hood off after a few minutes.
• Grease reaches places it shouldn't be — onto the fan housing, the motor shaft, the control board. The accumulated oil layer pulls in dust, and over time it traps heat and attracts moisture to the electronics.
• The hood itself starts to smell. The stale grease in the filter and on the blades becomes a smell source of its own — the air passing through carries it along.

This is a chain that regular cleaning can almost always break. Clogged filter → loaded motor → hot windings and worn bearings → a more expensive repair. If the hood already hums, rattles, or won't start at all, we cover that separately in Cooker hood won't start or hums.

When a clean filter saves the hood from the service centre

In the majority of "the hood doesn't pull anymore" call-outs, the first thing we check is the filter — and often that is where it all ends. But there is a line beyond which cleaning no longer helps and the bench is needed. Here is how to tell them apart.

The DIY line is simple. Safe self-help: removing filters, washing them, replacing the carbon filter, checking the air vents and the duct, changing a bulb. Anyone can do this with the hood switched off.

Beyond the line — service: anything that needs opening the motor housing, changing bearings, the capacitor, or the control board, or testing the windings. That involves mains voltage and parts that have to be chosen by model.

The honest principle: if suction recovers and the noise disappears after a carefully washed grease filter and a fresh carbon filter (in recirculation) — it was a maintenance case, not a repair, and no service is needed. If noise, overheating, or lack of suction remain even with clean filters, the problem is in the motor or the electronics, and that is judged at inspection.