Metal filters are found in a variety of larger home appliances where the wear and tear would quickly destroy a paper or fiber one. Examples are in a range hood, and in a furnace. One major advantage of metal filters is that they can be cleaned and used over and over again without the need to purchase a new one.
Take the metal filter out from the appliance and clean around the area. It does little good to put a clean metal filter back into a dirty area. Wipe any grease, dirt, lint or debris away with a commercial cleaner. If you are cleaning the ventilation or heating system, this is a good time to spray the area with an antibacterial solution to kill any mildew buildup. Washing will kill any on the filter.
Brush the obvious dirt and debris from the filter with a soft brush. Fine mesh can easily be damaged, so use a light touch. A kitchen filter will be greasier, while others might have hard mineral deposits. Both are treated similarly but the furnace or water metal filter may take another step to remove the lime.
Wet the metal filter and wash it with regular kitchen dish detergent. The detergent is designed to be gentle on material yet strong acting. If the grease deposits are thick on the range hood filter, let the suds sit on the filter for about 10 minutes before scrubbing the mesh. Be sure to get the bristles down between the mesh so that all the crud is removed.
After you've washed the filters, look for any leftover hard mineral deposits. Ordinary white vinegar should do the job of removing them for you. Brush the vinegar on the lime deposits and wait about five minutes. Vigorously brush the deposits, being careful not to hurt the mesh metal filter. If the lime stains are stubborn then soak a rag in vinegar and let the rag cover the deposits for an hour or two before brushing them again.
After hand cleaning, an easy way to return the sparkle to the metal filters is to wash them in the dishwasher. Place them on the upper rack, being careful that they will fit without being hit with any moving pieces. For range hood filters you can add standard dishwasher cleaning solutions, and for ones that have lime deposits you can add a cup of vinegar in a shallow dish place on the top rack. Remove and dry them when the washing cycle is complete.