Skip To Content

Does an Old Air Filter Really Affect My AC?

Forgetting to change the air filter for one month is no big deal. But if you let that same filter stay in place for six months to a year, you should be prepared for major repairs.

Everyone forgets to change their air filter from time to time. Life gets busy, and one-three months is a long time to keep track of a chore. No matter how important that chore may be. But how important is your air filter, really, you may wonder. After all, it's just a few layers of special wavy cloth and paper. Well, you're right; forgetting to change the air filter for a few days or even an extra month is no big deal.


Consequences for Keeping an Old Filter in Your AC Unit

But if you let that same filter stay in place for six months or more, the costs jump from "Don't Worry" to "Call the AC Repair Guy Right Now" kind of money. For that reason, it is important to know how an old, clogged air filter can have such a huge impact on your air conditioning system and why its important to change them regularly.

Airflow is Blocked, Reducing AC Efficiency

Okay, so your AC's efficiency is based on warm air flowing rapidly over very cold coils full of refrigerant. The coils are kept cold by the Compressor (that big thing outside the house), and the air flows in through the Intake where your filter is placed. The rate that warm air can flow over the coils, becoming cold air, is the rate at which your AC produces cold. The more efficiently it moves the air and compresses the coils, the more energy-efficient your AC is.

Now imagine that your filter is like a gate for the intake air. Like the turnstiles in a train station or football stadium. When it gets dirty and clogged, the gates close and less air can come through. Which means less airflow over the coils, less cold air through your vents, and to top it all off, your AC is now using extra power to compress the coils and spin the blower to meet thermostat demand. So dirty filters cause airflow to go down and power usage to go up, significantly decreasing your AC efficiency.

Dust Causes AC Refrigerant Coils to Freeze

Not only is that dirty filter blocking airflow and slowing down your AC, it's also starting to let dust through. An old filter loses the ability to effectively block all the dust and pollen in your air, like the people willing to jump those turnstiles at the train station. That dust gets into your AC unit which it is not supposed to do and sticks to the coils, which are always wet because the are cold and covered in condensation.

The dust sticking insulates the coils, keeping the cold locked in and preventing the warm air that does get through from picking up cold. So now your vents are blowing warm air and your AC is at risk of building ice and literally freezing up because dust has built up like a blanket over the super-cold refrigerant coils. This is also why not to run without a filter.

With Enough Time, Your AC Can Break

Between the increased dust and the decreased airflow, your AC is no longer running like a finely tuned machine. It is clocking the electricity over-time, trying to blow harder and make the coils extra cold, which is only making the problem worse. Over time, your AC interior can build up ice like an old chest freezer or break a part straining and come to an unpleasant rattling stop. Yes, it takes a while for an old air filter to break your AC, but it happens quite often because so many people completely forget that there's even a filter in there that needs changing.

Your Home Air Isn't as Clean

Now that we know how dirty air filters impact your AC, let us highlight how residents experience the problems caused by a dirty air filter, and how that air filter is affecting the rest of the home. To start with, the dust that is getting into your AC and blowing through the system is decreasing your home air quality. Rather than the AC constantly filtering dust and allergens out of the air, it's blowing them right back in through a filter that may not have been changed in years. So sometimes, years-old dust and pollen is being kicked through and into your lungs.

Your Allergies Will Get Worse

So it should come as no surprise if family members start experiencing increased allergies and asthma symptoms as a result of, not just dusty air, but ancient dust blowing through the house. You may start to get allergies that are out of season from old pollen blowing around, and anyone who suffers from year-round allergies will find no escape in the clean air of the home. Because your home air isn't clean. That's the filter's job and your filter is kaput.

Your Ducts Will Need Cleaning Sooner

In addition to filling the air you breathe and vacuum and walk through with dust and allergens, the old air filter is also filling your ventilation system with dust. Ducts always build up some dust, but the air filter is supposed to keep the air blowing outward clean and mostly dust-free. When extra dust is blowing through, that dust builds up inside the vents and will keep on blowing out for months even after you change the filter. Unless you arrange for a professional duct cleaning to solve the problem sooner.

The Real Cost of an Old Air Filter

When it comes down to it, the few extra minutes and spare thoughts you gain from forgetting about your home's air filter just aren't worth it. While it's no problem to forget for a month or two, a truly dirty and clogged air filter can cause problems so far beyond the cost of a filter or the time it takes to change it out. So set a timer. Use your smartphone, or smartphone, or online personal calendar as a reminder. And change your filter regularly. Because the long-term consequences of forgetfulness just aren't worth it.

Call (305) 805-8166 to ask how we can help.

Back to All FAQs