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How Often Should I Change My Furnace's Air Filter?

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Dan has been in the HVAC industry for 23 years, with experience ranging from installation and service to sales and distribution.

Out of sight, out of mind. That statement cannot be more true than when used to reference the furnace air filter.

Out of sight, out of mind. That statement cannot be more true than when used to reference the furnace air filter.

The saying "If I had a nickel for every time I..." applies here. I would definitely be well-to-do if instead of explaining why there isn't a magic number of days between air filter changes, people just gave me a nickel.

Most of those who ask me this follow up their question with the statement, "I'm told it's every 30 days". With that, I can't help but wonder, "Then why are you asking me if someone already told you that?" and immediately that thought is followed by, "...but I'm glad you did."

There Is No Set Time Between Furnace Filter Changes!

I'm sorry to say that there is no set time for you to change your filter. I'm not exactly sure where the "30-day rule" comes from. Perhaps it's the manufacturer who wants to sell more filters. Maybe it's because it's an easy number to remember. I really don't know, but I do know it's inaccurate.

So are you ready for the truth?

Keeping Your Filter Clean is Good for Your Air and for Your Furnace

Everyone's Air Filter Gets Dirty at Different Rates

If we stop and think about this for a second, we realize that the lady who lives by herself, doesn't do woodwork, and doesn't have any pets is hardly in need of changing her filter as often as her neighbor with a handy husband, four kids, and six cats. That's just one consideration to take into account when thinking about the frequency in which one should change their furnace filter.

Here are some other considerations and reasons why your filter may need to be changed more or less often than someone else's.

Things That Impact How Often You Should Change Your Filter

Many, many things impact how often a furnace's air filter should need changed.

Type of FilterRegionThe Home

Cheap filters tend to let more dust pass thus they need changed less often.

Some regions of the world simply have more airborne particles than others.

Older homes have a tendency to contain more dust.

Pleated filters catch more dirt so they may need changed more often.

Humidity can affect how much dust is airborne.

Carpet may trap dust particles while hard floors may allow it to take flight.

Media filters catch a lot of dirt and dust too but because they have so much more surface area they tend to last longer.

Ambient temperatures can dictate how often your unit runs thus how much air is being moved through the filter.

Do you have a boiler? Then I suppose you could stop here. You don't have an air filter.

Don't Forget About the Water Panel in Your Humidifier

While you're at it, change out this guy. These need changed yearly and I recommend doing so at the end of winter so the old one doesn't mold waiting for next season.

While you're at it, change out this guy. These need changed yearly and I recommend doing so at the end of winter so the old one doesn't mold waiting for next season.

How to Determine How Often You Should Change Your Air Filter

Air filters aren't really complicated in and of themselves. However, there are a few things that many people don't really think about when it comes to filters because, well, who spends large amounts of time thinking about their air filters? Okay, I do, but that's my job, so let me share some of this boring yet useful knowledge with you so that changing your air filter becomes a habit without becoming a pain and we can answer the question for often should YOU change YOUR air filter.

Decide Which Type of Filter You Want to Use

The first step is to determine what kind of air filter you think is best for you. Do you want to keep as much dust down as possible? Then you should look into a media style filter or at least a pleated one. Be aware that you may have to change it more often.

If you're horrible about remembering to change the filter and can live with a bit more dust passing through, you should probably stick with the cheaper, more porous filter so that it doesn't clog and end up burning up your motor or freezing your A/C due to lack of air flow.

If you just need a place to start, I really like these Filtrete MPR 1000 air filters. They have plenty good air filtration, but not so much so that you are constantly changing your clogged air filters (like you would with the MPR 1550s). They'll also filter out fine enough dust particles to help keep your air ducts clean and your furnace's longevity up.

Keeping Your Filter Costs Down

Obviously, the more porous filter is the cheapest way to go, but you can usually keep it even cheaper by buying these by the case, not to mention it's far easier to make yourself change the filter if you don't have to run to the store to buy them. There are usually case quantity pricing breaks if you buy these at a wholesaler or distributor. This same theory applies to most all filter types.

Your media filters are the most expensive option, and some are sort of a pain to change so look for "box" filters that might fit your air cleaner. These are typically cheaper and make changing the filter a snap.

How Often Do You Want to Filter Your Air?

Many homeowners don't realize they can keep their air cleaner than they do. Most home's air only gets filtered when the furnace or A/C is running, but if you turn the fan switch to "on" instead of "auto," you can continuously run the air in your home through your filter.

This will, of course, make your filter dirtier faster, meaning you may have to change it more often, but your air will be clean, and you'll likely notice the temperatures in your home to be more even throughout. I know what you're thinking, but running your fan won't cost you a lot of money. Once it's running, it uses very little electricity to stay running, and the furnace and a/c will still operate as it always has based on the call for heat or cool.

Setting a Reminder to Change or Check Your Air Filter

Now that you've made these decisions and bought your case of filters, set a reminder on your phone to check your filter in 30 days. If it looks pretty good at that time, then reset it for another 15 days and so on until you think it's dirty enough that it should be replaced. Once you've figured out how long that was for you, set your reminder to repeat for that time period.

Now you know how often you need to change YOUR furnace's air filter.

Keeping the Air in Your Home Fresh and Clean

Regularly changing your air filter can do a lot for keeping the air in your home clean, fresh, and healthy to breathe. If you want to go the extra step though, you should consider taking the time to clean your air ducts of all the dirt and debris that has built up over the years. That'll take your indoor air game to the next level.

If you simply need help getting rid of some of those bad smells coming from your home's air system, I wrote a guide to help you out called Furnace Smells: How to Reduce or Eliminate Odors in Your Air Ducts.

Thank You!

I do appreciate your taking the time to read my article. Feel free to contact me if you have an issue that isn't mentioned here and I'll do my best to help via cyberspace.

~ We're all in this together ~

What Did You Learn From This Article?

For each question, choose the best answer. The answer key is below.

  1. What filter is the cheapest but let's more dust in?
    • Media
    • Pleated
    • Fiberglass
  2. Can you vacuum your air filter?
    • Yes
    • No
  3. How often should you change your air filter?
    • Every month
    • Every year
    • You almost got me. Nice try.

Answer Key

  1. Fiberglass
  2. Yes
  3. You almost got me. Nice try.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2018 Dan Reed


Eman Abdallah Kamel from Egypt on September 14, 2018:

Thanks for this valuable information.

Dan Reed (author) on September 14, 2018:

Thanks RTalloni! LOL...yes, cheap filters for renters. Those calls make HVAC companies a lot of money!

RTalloni on September 14, 2018:

Excellent, and entertaining...who would've thought that possible with this topic?!

I've always wondered if I was doing the best thing by sometimes just vacuuming the a/c filter. So appreciate the info on the humidifier's water panel. (Just copied your husband will know whether we have one.)

Once we gave renters verbal and written instructions on changing out the a/c's filter. Months later when spring turned hot we got the inevitable call that the a/c isn't working.

Showing them the yucky filter and what they had been breathing did the trick.

Thanks for a definitely useful article.