Dirty Air Filter ComparisonThe best thing you can do to improve the performance your  furnace is to replace the air filter on a regular basis. Air filters are designed to pull dust out of the air as it circulates through the venting system allowing your furnace to work more efficiently. How well this process  works depends primarily on the type of filter and how much you want to spend. Obviously more expensive ones will do a better job to remove dust and other contaminants. Yes, this is another example in life of getting what you pay for, so you might want to take that into consideration.

Additionally not only can a dirty filter lead to higher energy bills but because your furnace is having to work harder to pass more air through the system to heat the home, damage can be done to it in the long run.

Whichever you choose, it is important to replace it on a regular basis. That schedule also depends on the type you choose and the recommendations by the manufacturer. The following filters represent the most commonly used by modern furnaces. Each type is listed from least expensive to the most expensive.

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Types of Furnace Filters

Spun GlassSpun Glass Filter

These are the least expensive and have been around since the 70s. However, they only remove about 15% of the dust in the air, so they do very little to actually protect anything except maybe preventing dust build-up on the inner fan of the furnace.

These cheaper types should be replaced every month with the old ones simply be thrown away. They cannot be washed or reused.


Next in line are fiber type filters which are a more modern version to spun glass. Similar to spun glass, they only absorb about 15% of all dust in the air, however, they can be washed which distinguishes them from the less expensive type.

MediaMedia Filter for Furnace

Media filters are probably the most commonly used ones used in American homes today. They typically are made from spun glass but have a core that consists of pleated fibers.  These types  are a huge improvement over the previous types because they remove anywhere from 45 to 90 % of all dust in the air. 

Media filters generally last for about 3 months depending on how heavy the furnace is being used. In fact, some furnaces may have slots for two filters at once, and some professionals recommend using a media filter along with a regular spun glass filter in front of it, acting as a filter for a filter.


These types are essentially the same thing as media filters with two main differences. First, electrostatic filters (as their names might suggest) are layered in a way to form an electrostatic charge that attracts dust in the air and pulls it into a foam filter.

Second, these are made of plastic so they are washable for reuse again.

One other type of electrostatic filter is called a High Efficiency Particulate Air (HEPA) version which will remove up to 99% of all dust and pollutants from the air. These are not washable however, and last for about 3 months.

Electrostatic Precipitators

The last major type of furnace filter is also the most expensive. An electrostatic precipitator filter operates in much the same manner as an electrostatic version, however, these filters are outfitted with a power source that constantly charges it.  These types of filter will block 99.999% of all pollutants in the household. 

Not only are these types of filter more expensive, but they are also difficult to install and maintain and best left up to a contractor in the HVAC industry.

Maintenance: Removing and Cleaning a Filter

How to Replace Furnace Filter

The most important thing you can do to maintain the life of your furnace is to clean or change the filter on a regular basis as directed by the furnace manufacturer. Depending on where your furnace is located, this can be a simple job or more complicated. Furnaces located in crawl spaces make it more challenging to change them on a regular basis, but is necessary nonetheless in order for the air to move through your home efficiently.

The cheaper types of filters are simply throw- aways, while others can be washed and reinstalled.

  1. With most disposable ones, you simply take off the furnace access panel and remove the dirty one. Most older furnaces have a groove within that holds it in place.
  2. Newer furnaces tend to have flexible metal arms that hold the filter in place. To remove the filter, lift up on the arm and swing it forward.
  3. Once removed, place a new filter within the slot in the furnace.

If you are using a washable, reusable type, try vacuuming the dust off it with a small handheld vacuum or attachment.  Then rinse it under cold water or lay it flat in a bathroom filled with 2 inches of water.

Note: You do not have to wait until the filter dries to reinstall it


Air will not travel efficiently through a clogged or dirty filter therefore it is important that you replace or clean it on a regular basis. Generally speaking, the more you spend, the more dust you will keep out of your home.

If you have really bad allergies, you may want to invest in one of the HEPA types described above as it will probably pay for itself in medical and prescription savings. In fact, if you are really concerned about contaminants in the air affecting your health, someone in your household has asthma or you have a lot of pets inside your home,  you may want to consider a "whole house media air cleaner" that you place in the living area and directly filters air constantly throughout the house

Filters are not an area to cheap out on because you are going to pay more one way or the other,  either through the cost of a quality filter maintained regularly, or the cost of increased utility bills, furnace repair bills down the road and possible health issues.