Why Does My AC Filter Get Dirty So Quickly?

Discover the reasons why your AC filter gets dirty quickly, including factors linked to HVAC filters and HVAC air filters. Contact Sandium for expert advice today!

Updated on Oct 22, 2023
5 min read
Why Does My AC Filter Get Dirty So Quickly?

All air filters tend to get dirty over time. If an air filter doesn’t get dirty, it means it is not removing particles from the air you are breathing in your Bay Area home. However, there are some reasons that can make the air filters clog quicker than usual. This can also cause performance and efficiency issues in the unit.

Reasons for Air Filters to Get Dirty Quickly

1. Temperature Concerns

If it is colder or hotter outside than usual, it could make the air filter get dirty faster. This is because the particle build-up on the filters is directly related to the amount of air being recycled through the air conditioner and furnace. If your system is running constantly, it will cause more air to flow through the filters, making them dirty quicker.

2. Fan is in ‘On’ Mode

There is a button on the thermostat that sets the fan on ‘auto’ or ‘on’. Systems with the fan set to ‘on’ will make the fan run constantly. This is even when the system is not in cooling or heating cycle. Air will filter through the unit constantly, which will cause particle-build up to occur that much sooner. You would need to change the air filters that much more sooner.

3. Pets in the House

Pets are terrific in the house. But, they can increase the amount of airborne contaminants inside the house. Pets are a major reason for air filters to clog quickly. You should change the filters at least once a month if you have indoor pets.

4. Increase in Number of People

An increase in the number of people living in a house means an increase in the amount of airborne contaminants. You should consider changing the air filters at least once a month to help with the overall airflow.

5. Construction or Remodeling

Construction and remodeling can make your house look more beautiful. However, the removal or addition or carpeting, tiles, and drywall can cause the air filters in your HVAC system to get dirty rapidly. You can protect the overall system by changing the dirty air filters as and when required during the construction project.

Replacing Air Filters

Generally, you would need to replace an air filter more frequently if it has a higher MERV rating. You should consider the filter’s rating if you think you are replacing it all too often. MERV rating is given to different types of air filters on the basis of the amount of air contaminants that it can catch. Higher MERV rating means that fewer airborne contaminants pass through it.

This is how quickly you need to change different types of air filters:

1. Fiberglass

Fiberglass filters need to be changed once a month. They are made from spun fiberglass and are usually an inch thick.

2. Pleated

These are made from paper or polyester. They are available in varying widths. These filters need replacing every 3 – 6 months.

3. Electrostatic

Electrostatic filters are washable and don’t need to be replaced. You can wash or vacuum the filters every month without any trouble.


HEPA filters are present in most air purifying systems. These need to be replaced every 12 – 18 months.

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