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Have you been neglecting your furnace filters? Don’t! A faulty filter can do a lot of damage to your furnace, even potentially causing it to break down. 

And, there’s one more reason to replace your furnace filters regularly. The most important one. Most people do not give indoor air pollution much thought. A grave mistake. According to the Environmental Protection Agency (EPA), indoor air is 2-5 times and sometimes even more polluted than outdoor air! 

Therefore, you need to either replace or clean your furnace filter on a regular basis in order to keep your HVAC system working to its optimal performance (and safely at that!).

Here’s everything you’d want to know about furnaces and their filters. This guide tackles eight important filter-related queries (with their answers of course!) for your benefit. 

How does a furnace work?

A traditional furnace draws air in, via return ducts, and warms it over a heat exchanger. It then pushes the heated air through ducts into your rooms with the help of a blower fan. The furnace runs till it reaches the temperature of your thermostat setting. 

During the summer, the air is cooled by an outdoor compressor unit and a series of coils inside the furnace.

FYI: Winter or summers, it’s crucial that you get regular furnace inspection to keep it in good working condition and your house safe. 

Read more: A Complete Guide on Furnace Replacement

What do air filters do?

Air filters, usually located inside the blower compartment of your furnace, work hard to protect your HVAC system and prevent the blower fan from collecting the gunk that the return duct pulls in. As a result, it removes contaminants such as dust, smoke, pollen, pet dander, bacteria, and mold dust mites from being recirculated. Furnace filters work almost like air purifiers — keeping you safe from allergens and bacteria. 

Why is it necessary to replace furnace filters?

Dirty air filterAngie changed the 312 furnace filter, by Collin Anderson on flickr [CC BY 2.0]

Not changing your furnace filters timely can be extremely harmful to the furnace as well as your indoor air quality. Moreover, you can save money on energy bills if you replace your home air filter regularly. The reason is that your HVAC will have to work twice as hard to push air through a dirty filter.

How are the filters rated?

Minimum efficiency reporting value or MERV rating is the measure of the efficiency of furnace filters. This rating system is standard across the industry. It ranges from 1 to 16. The higher the rating the more particles the filter is able to remove. And, the higher will be the price. 

Generally, a MERV rating between 8 to 11 is adequate for most homes. If in doubt, check with your furnace manufacturer regarding the adequate rating for your home.

What are the different filter types?

Types of air filterfurnace filter, by Gary & Anna Sattler on flickr [CC BY 2.0]

The most popular type is the disposable pleated filter. It’s constructed out of paper and polyester and does a good job at filtering most household particles and allergens. Keep in mind that such filters should be checked monthly for blockages and replaced every three months on average.

There are also disposable fiberglass filters that are the cheapest filters on the market. With a web-like appearance, they are more flimsy and have lower ratings than pleated filters. Since they are of inferior quality, fiberglass filters must be replaced more frequently.

Note that both disposable and washable filters are available as electrostatic versions. Electrostatic filters are especially helpful for homes with pets or people who smoke inside. These filters trap small particles and self-charge as air passes through them. 

The third category is that of permanent reusable filters aka washable filters. These are constructed with either solid aluminum or plastic frame. And, they are more efficient than disposable filters. 

The best part is that these filters can be easily cleaned with water (ideally after every 90 days) and last five years on average.

What are the common filter sizes?

Air filterAir filter, by HomeSpot HQ on flickr – HomeSpot HQ [CC BY 2.0]

Furnace filter sizes are measured by thickness, height, and length. The thickness varies from 1” to 4” while the height and length dimensions range from 10”x 10” to 30”x 30”.

The most common sizes are 14”x 25”, 16”x 20”, 16”x 25”, 20”x 25”, and 25”x 25”. 

Note: If you want to find out the size of your filter, simply look on the frame of the old filter, or refer to your furnace manual.

How often should you replace the furnace filters? 

Change your air filter at least once every three months. If you have pets or allergies — you can change them more often. Note that regular air filter replacement can lower your energy bills by up to 15%! And, your furnace will last longer.

If you’re not comfortable cleaning or changing your furnace filters yourself, it’s best to hire an HVAC professional for assistance.

How do you change the filters?

  1. Turn off your furnace
  2. Open the filter compartment door
  3. Slide the old filter out and dispose of it carefully
  4. Install the replacement air filter
  5. If you have a permanent filter, vacuum the dust off, rinse it with water, dry it, and replace it. 

It’s really important that you use the right air filters to make the air quality in your home clean and pure.

Planning a renovation for your house? Try our free home remodel cost estimator; it’s easy and convenient to use!

Want to Know Everything About Furnace Filters? was last modified: February 5th, 2020 by Ramona Sinha
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