Cooker Hood Carbon Filters Explained: What They Do, When to Replace Them, and How to Choose the Right One

How a carbon filter works

A carbon filter sits directly behind the metal grease filter inside the hood. As cooking air passes through, the activated carbon captures odour-causing molecules from frying, fish, spices, onions, and smoke through a process called adsorptionNot to be confused with absorption. In adsorption, molecules bind to the surface of the carbon rather than being drawn into its structure..

Adsorption works because activated carbon has an extraordinarily porous structure. Each gram contains an internal surface area of between 500 and 1,500 square metres — a structure created by heating organic material (typically coconut shell or coal) in a low-oxygen environment. Volatile organic compounds (VOCs), grease vapours, and odour molecules become chemically attracted to this surface and bind to it as air passes through. The carbon doesn’t absorb these molecules like a sponge; it binds them at a molecular level. Once the available surface area is used up, the filter can no longer capture odours effectively and must be replaced or, in the case of long-life filters, regenerated.

Critically, carbon filters do not remove steam or moisture from the kitchen air. That is a function of ducted extraction. In a recirculating hood, humidity stays in the room regardless of how effective the carbon is at removing smells.

Do you need a carbon filter?

Whether your hood needs a carbon filter depends entirely on how it’s installed.

Types of carbon filter

Carbon filters for cooker hoods come in three main forms. Knowing which type your hood uses before ordering is important — fitting the wrong type can reduce airflow and leave gaps that allow unfiltered air to bypass the carbon entirely.

Universal pads can seem like a convenient, cost-effective option, but they require a tight fit in the filter housing. Any gap allows cooking air to bypass the carbon layer entirely, rendering the filter ineffective. For best results, use the manufacturer-specified cassette for your model.

When and how often to replace

For a typical household that cooks once or twice a day, a standard carbon filter will last three to six months. Heavy daily cooking, particularly high-fat frying, curries, or strongly aromatic foods, accelerates saturation and may require replacement closer to the three-month mark. Light, infrequent cooking can extend filter life towards six months.

Many modern hoods include a filter saturation indicator or timer that illuminates after a set number of operating hours — typically 30 to 60 hours of use. This is a useful reminder, but it counts running time rather than actual saturation, so it’s worth cross-referencing with the nose test: if smells are returning to the kitchen during cooking despite a running hood, the filter has likely reached its limit regardless of what the indicator shows.

Signs your filter is saturated

A carbon filter doesn’t fail dramatically — it degrades gradually. These are the most reliable signs it needs replacing:

How to replace a carbon filter

Replacing a carbon filter takes a few minutes and requires no tools. Always consult your hood’s manual to confirm the correct fitting method for your specific model — twist-lock cassettes and clip-in cassettes differ slightly in how they seat.

1. 1
   Switch off the hood and allow it to cool

   Never remove filters while the fan is running or the hood is warm from use.

2. 2
   Remove the metal grease filters

   Most release by pressing a latch or tab on the underside of the hood. Set them aside — this is also a good opportunity to check whether they need a wash.

3. 3
   Locate the carbon cassette(s)

   Round cassettes are typically mounted on the motor housing centrally; rectangular cassettes clip into a frame behind where the grease filters sit.

4. 4
   Remove the old filter

   Twist anti-clockwise to release a round cassette, or unclip the retaining tabs for rectangular types. Dispose of standard cassettes — do not attempt to wash them.

5. 5
   Fit the new filter

   Align the tabs and twist clockwise (round cassettes) or press firmly until the clips engage (rectangular). A poor seal allows air to bypass the carbon, so confirm it is fully seated.

6. 6
   Refit the grease filters and test

   Run the hood on a medium speed for a minute to confirm normal airflow. Reset the filter indicator if your hood has one — typically a long press on the filter reset button.

Choosing the right filter for your hood

The most reliable way to find the correct carbon filter is to match it to your hood’s model number, found on the rating label inside the hood (usually visible after removing the grease filters). Use that code to search for the genuine spare part or a confirmed compatible replacement. Avoid selecting a filter by diameter alone — even cassettes that appear similar can differ in depth, tab position, or carbon density, all of which affect both fit and odour capture.

Denser carbon improves odour capture but can introduce a small reduction in airflow, as measured in m³/h. Using a filter specified for your model ensures the right balance between odour control and extraction performance. If you’re finding that smells return too quickly on the manufacturer-specified interval, upgrading to a long-life cassette (where available for your model) often gives better odour performance thanks to a higher carbon mass per cassette.

For a broader look at how filter condition affects extraction performance over time, the guide to cooker hood extraction rates covers how both grease and carbon filters influence real-world airflow figures. And if you’re troubleshooting a hood that isn’t performing as expected, the common cooker hood problems guide walks through the most frequent causes.

For further guidance on ventilation standards in kitchens, Approved Document F from the UK government sets out the building regulations requirements for domestic kitchen ventilation.

Frequently asked questions