I pulled the metal filter out of my range hood and could not see through it. It was a solid sheet of yellow-brown grease.
I nearly bought a new one. Then I put it in the sink with boiling water and dish soap, and twenty minutes later it looked new.
The Method That Actually Works
Boiling water, dish soap, and baking soda. In that order, and the water has to be genuinely boiling — hot tap water will not do it.
Fill the sink or a roasting pan with boiling water. Add a good squeeze of dish soap and about a quarter cup of baking soda. It will fizz a little.
Lay the filter in flat. If it does not fit, do it in halves.
Leave it fifteen to twenty minutes. Do not scrub yet.
Then lift it out and go over it with a soft brush. The grease comes away in sheets rather than smears.
Rinse with hot water and let it dry standing up before it goes back.
Why Boiling Water Matters So Much
Old range hood grease is solid at room temperature. Cold or warm water cannot dissolve a solid — you are just pushing it around.
Boiling water melts it back to liquid. Once it is liquid again, the dish soap can do the only job dish soap does: grab onto fat at one end and water at the other and carry it away.
The baking soda raises the pH, which helps break down the fat itself rather than just lifting it.
This is the whole reason people report that “degreaser did nothing.” They used it cold.
If It Is Really Bad
For a filter that has never been cleaned, do it twice. The first round takes off the loose top layer and the second gets down to the metal.
A dishwasher on the hottest cycle also works for a stainless mesh filter, but it will not cope with years of buildup on the first run either.
What Not to Do
Do not use oven cleaner on an aluminum mesh filter. Caustic oven cleaner eats aluminum and will leave it pitted and chalky. Many hood filters are aluminum.
Do not put a charcoal filter in water at all. Charcoal filters are not washable — they get replaced. Only metal mesh filters get cleaned.
Do not use a wire brush. It flattens the mesh and reduces the airflow permanently.
How Often
Every three months if you fry or cook with oil often. Twice a year otherwise.
A greasy filter does not just look bad — it chokes the airflow, so the hood stops pulling steam and smell out of the kitchen. Half the people who think their vent hood is weak just have a blocked filter.
Do It This Weekend
It takes twenty minutes, most of which is waiting.
And the filter you were about to replace almost certainly does not need replacing.
