September 19, 2023

What Happens When You Don’t Change the AC Filter

Why don’t you change your AC filter?

Filters become a low priority due to a misunderstanding of what filters actually do. Standard HVAC filters are not intended to purify the air you breathe. Sure, the filter does trap some dust that gets sucked into the ducts. But most filters aren’t fine enough to trap pollen, dander, particulates and other allergens.Your standard AC filter’s main job is to protect the AC unit itself from harmful things in the air. Once you change your AC filter, you make it much easier for the AC to keep you cool.

IMPORTANT NOTE: There are higher efficiency HVAC filters that are designed to remove allergens, bacteria, mold, and even viruses. 

If you have upgraded to a higher efficiency filter, as part of a COVID mitigation strategy or just to alleviate allergy symptoms, it’s important to know that these filters need to be changed more frequently than standard HVAC ones. Because they trap more debris, they get clogged faster.

Read on to learn about what happens to your AC equipment when you don’t change the AC filter.

Buildup on blower fans and ductwork

Filters aren’t designed to screen the air forever. Eventually, they fill up with captured dust and dirt. Depending on your system, you should either change your AC filter or clean it. Paper filters are disposable, with cardboard frames and a paper screen. Sturdier filters are reusable, usually with metal frames, and can be cleaned according to manufacturer instructions. If you don’t change your AC filter, it will begin to fail. It will no longer be able to filter the air properly, letting dust and contaminants get into the AC. Dust jams the moving parts of an AC such as fan motors and valves. Airflow is restricted which creates a strain on the system. The HVAC system will draw more power to overcome the obstacle. This is how dust makes the unit less energy efficient (at best) and can lead to breakdowns. When you change the AC filter each month during peak cooling season, you can save about 15% each month on utilities, plus prevent repair issues due to airflow restrictions.

Moisture and mold contamination

The next effects to worry about are the other contaminants that enter a dirty system. The only type of filters that catch allergens and spores are HEPA, or high energy particulate air filters. These are made of a much finer mesh than other filters, and so can screen out tiny particles such as allergens, pollen, dander, and mold spores. They are categorized by MERV ratings 1 through 20. The higher the rating, the more effective it is at catching small particles. HEPA filters can give you better indoor air quality.

IMPORTANT: Not every system can accommodate higher efficiency filters, especially HEPA and MERV 13 filters that are being recommended due to COVID. Always consult with an expert before upgrading filters!

If you have a higher efficiency filter and fail to change the AC filter often enough, a buildup of moisture can cause mold to accumulate in the ducts, leading to serious mold infestations. The air in your AC filters through the system five to seven times a day. That’s a lot of circulation, bringing whatever’s inside your AC with it. Pollen, mold, and germs will quickly spread throughout any building. All of the above can make people sick. Change the AC filter and avoid Sick Building Syndrome. Your employees will thank you for not making them suffer through allergies and illness.

Wear and tear

Over time, the problem will get worse if you continue to ignore it. The filter itself isn’t the only thing that will stop functioning as it should. Dust in the ducts will degrade the moving parts, making them run slower and draw more power. This will wear out the mechanics of your AC much faster than normal use. The average lifespan of an HVAC unit is fifteen to twenty years. Without a regular change of the AC filter, that can be shortened by five to ten years. Eventually you will have to replace parts of your AC as they break, and that can get expensive. Consider the minimal cost of filters as an alternative to the much greater cost of larger repairs. That doesn’t even take into account the business you might lose if you have to close for AC repairs or replacement.

So are you convinced to change your AC filter? Great! Here is some information you need to know about the process.

How to change the AC filter in 3 steps


n some AC systems, filters are in the return air ducts. If you have one system that handles both heating and cooling, you can find the filter in or near the blower system. For a heating system, a filter is usually found near the air circulation for a furnace. To locate it you may have to determine which return air duct the filter is in. Look for the filter in front, near the bottom of the furnace. Access to the filter will either be open, or it will be covered by a metal panel labeled “filter.” The metal panel may be attached with hooks or screws.


Once you have located it, you must choose the right replacement to change your AC filter. To choose the correct size filter for your unit, check on the side of the screen already in place. Size is usually printed on the side. If you are replacing an old or disposable filter, you should also consider getting a HEPA filter to catch contaminants.If you’ve never changed your AC filter before, the easiest way is to have a HVAC technician do it the first time. They can show you where the filter is, how to access it, and what needs to be done to clean or replace it.


If you decide to change the AC filter yourself, you need to know how to do it safely.The first step? Always turn off the power before messing with your AC. This not only keeps you safe while you work on it, but it also prevents dust from getting sucked into the unit while the filter is off. Next you need to open the panel, and slide out the old filter. Hold the filter up to the light. Can’t see through it? It definitely needs to be cleaned. Disposable cardboard filters can be thrown out and replaced. Reusable filters should be cleaned according to manufacturer instructions, which your HVAC tech can help you with. Then, find the arrow on the new (or cleaned) filter. This should point away from the return air duct when inserted. Once oriented correctly, the filter can be placed back in its slot. Secure the metal panel and you’re done for the month.

Isn’t that satisfying? You’ve completed an important step for keeping your AC unit running reliably and efficiently.

Here’s something else to be aware of. If you neglected AC filter change for some time, there’s a good chance you have a lot of dust buildup inside your ductwork. You may want to consider having your ducts inspected to see if you need duct cleaning. Clean ducts not only make your system work better, but they improve indoor air quality as well.

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