How to Locate a Furnace Filter

Furnace filters prevent debris from getting caught in your furnace’s fan, and they also provide air filtration for high quality, clean air. BBJ Environmental Solutions recommends changing heating, ventilation and air conditioning filters every one to six months, but this can be difficult if you don’t know how to locate the filter on your home’s primary heat source. Luckily, locating your furnace’s filter is relatively simple if you follow the right steps, allowing you to keep up with this vital part of home maintenance.

Things You'll Need

  • Screwdriver
  • Gloves

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Listen for the whirring sound of a fan inside the furnace to help guide your hunt for the filter. Donald Munn, a HVAC technician with over 20 years experience, says early air filters were primarily used to keep debris from getting caught in the fan. While modern filters have been designed to purify the air for better environmental and home health, the placement is still traditionally kept close to the fan.

Look for a slot measuring about 1 inch by 15 to 25 inches somewhere near the whirring sound. Traditional furnace filters simply slide in and out of thin slots. The compartment for a furnace filter will never be very large in order to prevent heat loss through the opening.

Look for an electronic device that looks similar to a desktop computer tower. If you notice such a device, chances are you have a “media filter” enclosure. These enclosures hold nontraditional 4- to 6-inch thick filters according to IAQ Source, a distributor of furnace parts and accessories. If you locate a media filter enclosure on your furnace, you can access the filter by unscrewing the front panel on the enclosure.

Turn off the furnace. If you have not yet located an external slot for the filter or a media filter enclosure, chances are your filter is located inside the main furnace unit itself, and you always need to turn off the heat before checking inside. Remember that a deactivated furnace can still be extremely hot, so wear thick work gloves to prevent accidental burns.

Open up the main access panel on your furnace. In most cases the main panel will pop right off, but sometimes a screwdriver is needed. Upon opening the access panel, you should notice the filter somewhere near the return air duct, housed just in front of the unit’s fan.

Tips & Warnings

  • Always turn off the furnace before opening it up to look for an internally located filter. Failure to do so can result in serious injury.


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