Why is My AC Filter So Dirty? A Florida Tech Answers

August 16, 2020

Dirty Vs Clean Filters

Have you replaced your AC air filter and wondered how it got so dirty?

We’ll start by saying that it’s completely normal for your air filter to collect dirt and other debris. On average, you should replace your air filter every 1-3 months (depending on how often your AC is running).

However, if you notice that your AC is dirty enough to replace more often than that, there is likely an issue.

A few reasons your air filter may be getting really dirty, really fast are:

  • The thermostat is set to ON instead of AUTO
  • You have leaks in your air ducts
  • You have pets
  • It’s extremely hot out

Below, we will look at each of these in more detail, so you can get a better idea of what is causing your air filter to become dirty and if there is anything you can do to prevent it.

Want advice from a professional? We’d be happy to take a look. You can learn more about the AC repair services we offer or schedule an appointment online!

Issue #1: The thermostat is set to ON instead of AUTO

On Vs Auto Setting on Thermostat

Example of the proper FAN thermostat settings.

One of the most likely reasons that your air filter is getting dirty is because your thermostat is set to ON instead of AUTO.

When your fan is set to AUTO, it will blow air into your home ONLY when that air has been cooled by your AC system.

When your fan is set to ON, it will blow air constantly, even when that air has not been cooled by your AC system.

When your fan is set to ON, it means your AC is constantly pulling in warm air from your home and circulating that air throughout your home. This also means air is constantly being filtered, which is why the air filter will become really dirty if your AC fan is ON.

When your fan is set to AUTO, your AC only pulls in air during a cooling cycle, which means your air filter is being utilized a lot less than if your fan is ON and pulling in air constantly.

To help prolong the life of your air filter and reduce your energy bills, your thermostat fan setting should be set to AUTO at all times.

Issue #2: You have leaks in your air ducts

If you have leaks in your return ductwork, it means that air from spaces around that ductwork (usually the attic or a crawlspace) is being sucked through your air filter.

Why does this make your air filter so dirty?

Well, air from unconditioned space like your attic or a crawlspace is usually full of dust and other particles, which can cause your air filter to clog faster, especially if your air filter is located right next to your indoor AC unit.

Example of an air filter that's located right next to the indoor AC unit

If you notice that your home feels warmer (even though you haven't changed the temperature on the thermostat) and/or your energy bills have increased, you may have leaks in your ductwork. You should contact a quality HVAC company to come and take a look at your ducts. If there are leaks, they will need to be repaired by a pro.

Issue #3: You have pets

If you have pets, it’s pretty likely that your air filter will become really dirty in a shorter time frame. If you have pets, you’re probably used to finding pet hair on your furniture, rugs, floors and other surfaces of your home.

Pet hair also circulates in the air, and will eventually get caught by your air filter as your AC pulls in air from your home to be cooled.

If you have a pet, unfortunately, you may have to replace your air filter more often than every 1-3 months. However, there are a few ways to reduce the amount of pet hair and other debris that can get caught in your air filter, like:

  • Brushing your pet regularly outside so that the hair does not make its way into your home.
  • Vacuuming your furniture and floors regularly so that pet hair is removed and not kicked up into your home’s air.
  • Dusting your home regularly to prevent hair from making its way into the air or onto other surfaces of your home.

Issue #4: It’s extremely hot out

Another possibility to consider is the outside temperature. Your AC can only cool your home so many degrees. If it's 95 degrees outside and you have your thermostat set to 68 degrees, your AC is going to be running almost constantly to try and meet that demand.

The more often your AC cycles on, the more air is being sucked in through the air filter and the dirtier the air filter will get.

If it’s very hot out, you should consider increasing your indoor temperature a few degrees to give your AC a break. This will decrease the number of times your AC is cycling on during the day and the amount of air that is being sucked through the air filter.

Think you may have an issue with your AC system? Red Cap can help!

If you think your air filter is clogging because of an issue with your AC system, we’d be happy to take a look. All of our HVAC techs are highly trained, so no matter what’s going on with your AC system, you can trust us to accurately diagnose it.

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