Dryers that don’t dry, vacuum cleaners that don’t clean, and air conditioners that don’t cool may all be plagued by the same problem: a clogged or dirty filter. To keep many top-performing appliances in tip-top shape, you have to clean or replace a filter. In fact, that’s the first thing to check when something seems awry. When Consumer Reports tests vacuums, air conditioners, dishwashers, and other appliances, filter replacement is one of the things we consider as part of our ease-of-use score.

Any appliance with a filter that cleans air or water needs attention. How often depends on how much you use the appliance and what the manufacturer recommends to get optimal performance.

“Some of your appliances are so essential to keeping your home clean that it’s easy to forget that cleaning your appliances should also be part of the annual springtime ritual of scrubbing, polishing, and purging,” the Association of Home Appliance Manufacturers recommends.

Here’s our experts’ advice on the filters you should change or replace and how often:

Filtering Water

Refrigerators
If you have a water dispenser or an icemaker in your fridge, you’ll need a filter to remove small particles or contaminants, such as lead and chlorine, and impurities that cause bad tastes or odors. The filters have to be replaced periodically following the guidelines in your owner’s manual, often twice per year. If your refrigerator’s water-supply line uses a filter, replace that, too.

Dishwashers
Dishwashers are equipped with either an automatic filter that grinds food particles so that they wash away with the wastewater or a manual filter that you need to clean yourself. The grinders can be noisy, so quiet dishwashers often have manual filters. They should be cleaned at least every three to six months depending on how often you use your dishwasher. Some manufacturers recommend cleaning the filter every two or three weeks, so check the owner’s manual. “Dirty filters won’t damage a dishwasher but will affect its performance,” says Larry Ciufo, who tests dishwashers for Consumer Reports. Be sure the heating element has cooled down before you reach into the machine.

Carafe Water Filters
Water filters have different lifespans depending on the type. Typically, the filter in a carafe water filter is good for 40 gallons. It’s up to you to keep track because few carafe water filters indicate when it’s time to change the filter. Failing to periodically change the filter can result in water that’s dirtier than before you filtered it. Our water filter ratings include the yearly filter-replacement cost for each model; it ranges from $30 to $180 annually.

Mounted Water Filters
Some water filters connect to your water line under the sink or mount on your faucet to filter out sediment, lead, and other contaminants. The filters should be changed periodically, usually after 100 gallons or about four months. Some have built-in indicators that let you know when it’s time. Check the manufacturer’s instructions for your model’s recommended maintenance schedule. The replacement filters range in price from $40 to $400.

Filtering Air

Air Purifiers
An air purifier can choke on dirty air if the filter is soiled, and if it’s completely clogged, the machine may stop working entirely. Most of the air purifiers in Consumer Reports’ air purifier tests have a filter indicator that tells you when to check the filter or prefilter. You can often clean prefilters, but the main filter should be replaced following the timetable in your owner’s manual. We include the expense in the annual costs we list in our ratings.

Keep in mind that not all filter indicators are foolproof. Though some newer air purifiers tell you it’s time to clean or replace a filter based on how much you’ve actually used the unit, others base their recommendation on a set number of hours. “So if you run your purifier less often, you should inspect the filter before tossing it to keep from replacing it unnecessarily,” says Dave Trezza, the engineer who oversees our air purifier tests.

Vacuum Cleaners
Failing to change the filters in your vacuum cleaner may cause it to lose suction or spew dust back into the air. Changing the filters regularly, especially on bagless models, saves work and aggravation. Frank Rizzi, who tests vacuums for Consumer Reports, says that every model is different, so you should consult the owner’s manual to see how often the filters should be changed and whether they’re washable. If you no longer have the manual, you can usually find a copy online.

Dehumidifiers
A dirty filter can inhibit the performance of your dehumidifier (shown below). Most can be easily removed and cleaned in just a few minutes. Don’t neglect this task just because your unit is out of sight in the basement. Keeping the filters clean will improve the air quality and keep your machine working at its best. This is especially important when the humidity is high because humidity levels above 50 percent can lead to the growth of dust mites, mildew, and mold.

Range Hoods
Wash or replace the filters every one to three months—or more often if you cook frequently. Some have filter-maintenance indicators that let you know when it’s time. Slide the filter out of the range hood and into a sink filled with hot water and a good degreasing soap. Let it soak for at least 10 minutes. Use a sponge to carefully remove any remaining grease or debris. Then air-dry and replace.

Microwave Ovens
Over-the-range microwaves also have filters that need attention. A greasy filter results in a fan that can’t exhaust properly or capture cooking fumes, leaving a sticky film on appliances and kitchen walls. To keep it clean, wash the filter in warm, soapy water at least twice per year and more often if you cook at home every night. Some microwaves have dishwasher-safe filters. “If your filter has grease buildup, it can start dripping on your cooktop,” says Larry Ciufo, who has tested microwaves for Consumer Reports.

Clothes Dryers
A dirty lint filter extends drying time, using more energy and costing you money. In addition to cleaning the lint filter before every load of laundry, you should inspect the dryer duct and cabinet regularly to check for any lint buildup, which poses a fire hazard. This should be done according to the owner’s manual. Some newer dryers have blocked-vent sensors that detect reduced airflow, but not all performed well in our clothes dryer tests, making a visual inspection the safest bet.

Gas Furnaces
To keep your forced-air heating system in peak condition you should change the filter every few months. A dirty filter can prevent proper airflow, leaving the air unfiltered and the furnace struggling. The best way to get a proper fit is to remove the old filter, taking note of the size and the arrow that indicates the direction of the airflow—both should be printed on the filter. One of the biggest mistakes people make doing this chore is putting the filter in backward.

Central Air Conditioners
If you have a combined forced-air heating and cooling system, you only need to change one filter. If the central A/C is separate, plan on changing the air filter at least once per month during the cooling season. Consider buying a service plan. Many cover both cooling and heating systems. At the beginning of each cooling season, make sure your service contractor changes any filters, in addition to other maintenance checks.

Room Air Conditioners
All window air conditioners have a filter, and many come with a filter indicator that signals when it needs cleaning. If yours doesn’t, check the filter at least once per month during periods of heavy use. When the filter is dirty it affects the unit’s ability to cool your space. Remove the filter and use your vacuum’s upholstery brush to vacuum away the heavy dirt, then wash the filter in the kitchen sink, using a mild solution of dishwashing liquid and warm water. Wait until it’s dry to put it back in. “Some filters are easier to remove than others, so check that when you’re in the store,” says Christopher Regan, who oversees our air conditioning tests.

Bathroom Exhaust Fans
Dust your exhaust fan with a vacuum-cleaner brush or a damp cloth. If the fan covers can be removed, wipe down the blades and other non-electric parts twice per year with a cloth sprayed with or dipped in an all-purpose cleaner, and clean or replace the filter.

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