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How Often Does a Furnace Filter Need Changed and Other Tips

Even if you are all thumbs, there is one home maintenance project that just about anyone can handle: changing the filter on a forced-air heating and cooling system. Changing the filter can make your home more comfortable because the system will be more efficient at cleaning the air, and a clean filter may help prevent costly HVAC repairs in the future.

Locate the Filter

Filters need to be changed, or cleaned if it is a reusable model, because they prevent the dust and other impurities that circulate through the forced-air system from coming in contact with the blower motor and the compressor coils. The filter is located just before where the return air enters the furnace cabinet.

At the very least, change the filter at the start of the heating season and again at the start of the cooling season if the system includes air-conditioning. Some people recommend changing the filter monthly, others every three months. Here's another strategy: Change the filter and then check it in a month. If it looks relatively clean, reinstall it and check it in another month. The goal is to create a schedule that meets the needs of your particular system.

Changing the Filter

Check out our video and step-by-step guide on changing out your furnace filter.

  1. Determine the size you need. Filters come in a variety of sizes. The information will be in the owner's manual that came with the furnace. If you don't know the size you need and you don't have a manual, go to the next step.
  2. Turn off the unit. This will prevent the furnace from clicking on while you are working. There should be a switch nearby or you may have to cut the power at the panel box.
  3. Remove the filter enclosure door. Sometimes finding the door can be difficult. Again, consult the manual. You may be able to download a copy from the manufacturer's website. If you are still stuck, call in an HVAC technician for routine maintenance and watch what he does. In any case, an annual maintenance visit performed by a professional can prolong the life the system.
  4. Pull out the old filter. The dimensions will be listed on the filter frame. This is the size you should buy. Standard filters are 1-inch thick, but there are thicker ones available. But without altering the system, you should use the size filter that fits the filter compartment of your system.
  5. Slide the new filter in place. On the frame of the filter will be arrows that indicate the direction of the air flow. The arrows should point toward the blower and away from the cold air return. Reusable filters can be vacuumed or cleaned with water. Let them dry completely before reinstalling.
  6. Replace the cover door. With the door in place, apply duct tape to any exposed seams to prevent air leaks. Use foil-backed tape designed for ducts; don't use the fabric-backed tape that is called "duct" tape.
  7. Turn the system back on.

Types of Filters

The standard furnace filter is a fiberglass or polyester flat filter that keeps large dust particles out of the system. But there are pleated filters, which have more surface area for trapping particles, and filters that contain an electric charge, which can filter out very small contaminants. These more efficient filters are designed to improve the air quality in the home. They remove such contaminants as mold spores, bacteria and microscopic allergens—some of the most efficient filters can even remove odors.

You can determine how effective a filter is at removing specific contaminants by checking the filter rating. There are a few rating systems. The Home Depot's Filter Performance Rating (FPR) is fairly straightforward and easy to follow. Filters are rated from four to 10, with the higher numbers removing the smallest contaminants. Filters are tested by an independent third party. Here's more information about the rating system, including the contaminants filters can remove from the air in your home.

Before substituting a standard filter with one that removed more contaminants, discuss your plans with an HVAC technician. Some filters can reduce air flow in the system, making the blower motor work harder. This could lead to damaging the motor.

Changing the filter in a forced-air heating and cooling system, is an easy way to keep the equipment working properly.

About the author:  Home improvement writer Fran Donegan shares his knowledge of DIY and writes foThe Home Depot. Fran provides advice on how to complete projects such as changing furnace air filters.

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