The Effects of a Dirty HVAC Air Filter

And What You Can Do about It

You rely on your heating and air conditioning to keep your home comfortable. There’s nothing worse than losing AC in the middle of August. That’s why it’s so important to take care of your HVAC system. It needs plenty of TLC to function at its best.

Aside from regular maintenance like duct cleaning and electrical checkups, changing your air filters is one of the simplest things you can do to keep your heating and AC systems running smoothly.

The effects of a dirty air filter are much more than you might think. A dirty air filter can decrease the efficiency of your system and even bring it to a screeching halt. Here’s what happens when your air filter gets clogged.

It Makes Your HVAC System Work Much Harder

It’s simple physics. With a clogged air filter, air flow becomes more difficult. Your HVAC unit’s air handler has to work harder to keep things moving. The extra strain on the fan motor can, over time, cause the fan to go out and overheat the unit causing damage.

It Could Freeze the Evaporator Coils

Evaporator coils are a part of your AC unit. They absorb heat from the house as air circulates over them. If your air filter is dirty and air flow is decreased, the coils can get too cold and freeze up. The entire system will shut down while the coils thaw then start up again.

Not only is it hard on your system for it to function this way, you won’t be able to keep temps where you want them. The ultimate result is extreme inefficiency and that means $$$.

It Will Cause Your System to Run More Often

Another effect of a dirty air filter is more frequent cycling. Decreased air flow will leave warm spots throughout your house and the system will cycle on more frequently to try to balance that out. Turning on and off more often actually uses more energy than if you were to run it longer at a lower setting. It jacks up your energy bill without giving you much to show for it.


New vent cover on a wall vent in a room with a lamp and dresser.


It Makes Everything Dirty

A dirty air filter allows more dirt through into your system making your ducts and HVAC unit dirtier than they would be with regular air filter changing.

That might introduce a whole new set of problems (like mold and mites) not to mention tanking the air quality in your home. An air filter keeps dirt out of your system but it also filters out spores, pollens, pet dander, and dust that can make allergies flare up.

It Increases Moisture

Decreased air flow because of a dirty air filter makes it difficult for your HVAC unit to control humidity. In the dog days of summer, that can be quite uncomfortable but there are even darker forces at work. Increased moisture might lead to mold and mildew on your filter or throughout your system, which could lead to spores blowing through your house.

What You Can Do

Annual HVAC checkups are a good preventative measure to keep your system functioning efficiently all year long. Even more importantly, change your air filters as recommended by your HVAC professional.

How often you should change your filters depends on several factors like the type of filter, size of your house, where you live, how many occupants live in your home, whether you have pets, and if you have people with allergies.

As a general rule, you should be replacing your filters every 3-6 months. If you have pets or allergies, more frequent changing (20-40 days) is advisable. If you have no pets, live alone, or aren’t in your home very often (vacation home) you can get away with 6-12 months between changes.

You can also determine how often you need to change air filters by checking them. Remove the vent cover, then without taking the filter out, shine a flashlight on the filter and observe its color. The level of graying indicates how dirty the filter is. You can also try the white sheet test by hanging a sheet about five inches from the vent for a minimum of an hour then observing how dirty the sheet becomes.

More frequent allergy attacks, more dust, and increased electricity bills can all be indicators of a problem with your system as well. Start by changing the air filters to see if that solves the problem.

If your HVAC system is showing signs of distress, take a closer look at your air filters. The effects of a dirty air filter can influence your health, the efficiency of your system, and how well it works.

While you’re at it, consider giving your vent covers a good cleaning too. Here’s our guide to how to do that.

Learn How to Clean Vent Covers

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