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What Causes a Wet Air Filter in an HVAC System?

Let’s imagine that it’s time to replace your HVAC air filter. Everything is going as usual until you remove the old air filter. For some reason, the air filter is damp, and wet air filters are not normal.

Any time something is out of the norm with your HVAC system, it warrants looking into. You can replace the wet air filter with a dry one, but the problem causing it needs to be addressed.

What Causes a Wet Air Filter

Did you know that your HVAC system creates moisture? Even though the air inside can get dry from constantly running the HVAC equipment, condensation is forming and dripping into a condensate pan connected to drain lines behind the scenes. The pan and drain lines are designed to collect the condensation, so it doesn’t cause moisture problems.

Now you may be thinking, “that makes sense, but why is my air filter wet if there’s a pan to catch the condensation?” A few things could be happening, but the root of the problem is almost always condensation that isn’t draining from the evaporator coil properly.

Clogged Drain Lines
One of the most common causes of wet air filters is clogged drain lines that cause the condensate pan to overflow. The condensation can spill out and leak onto the filter.

Drain Leaks
Leaking drains are another common problem. A drain leak can cause water to pool at the bottom of the HVAC unit and eventually flow down to the filter.

Clogged Condensate Pan
There could also be a clog in the condensate pan that prevents water from seeping into the drains. When that happens, the water will overflow out of the pan.

Moisture Falling From the Evaporator Coil
If your HVAC system wasn’t installed correctly, the condensation could be dripping from the evaporator coil directly onto the air filter.

Two other less likely causes for a wet air filter are:

Air filter placed incorrectly. If the air filter isn’t inserted correctly, moisture from the evaporator coil could contact the filter.

High humidity levels in the home. Humidity may be high due to the regional climate or moisture problems inside that generate from a source outside the HVAC system. For example, there could be a leak in the home that adds extra moisture to the air. However, usually, the humidity level isn’t high enough to make an air filter wet.

Why You Shouldn’t Ignore a Wet Air Filter

One should not ignore wet air filters. They indicate that there is a moisture problem inside the house, which is something that needs to be taken care of immediately.

Anytime there’s excess moisture, mold growth can follow. This is a safety concern for the people living in the house, and it can damage the structure of the home. Excess moisture can also cause problems in the HVAC system that damages equipment and reduces efficiency.

Tips for Preventing and Fixing Wet Air Filter HVAC System Problems

Here are three simple steps in preventing problems that cause wet air filters:

Change the air filter regularly to prevent clogs. The easiest way to avoid clogs in the drains and pan is to change your air filter at least every three months.

Choose the right air filter. The best filter in an HVAC system is from an original manufacturer and appropriately sized for an exact fit. Choosing a high-quality air filter that can catch more air particles also helps prevent clogs.

Schedule regular HVAC maintenance. Clearing the drain lines and cleaning the pan is a standard part of professional HVAC system maintenance.

Wet Air Filters FAQ

Below our air filter experts answer a few more common questions related to wet air filters.

Why is My Air Filter Wet in My HVAC System, and is it Normal?

There could be a few different reasons for the wetness, but it isn’t normal. You’ll need to inspect the HVAC system to pinpoint where the moisture is coming from.

What Causes an Air Filter to Become Wet?

Generally, there is a condensation drainage issue in the HVAC system that causes air filters to get wet.

How to Prevent Air Filters From Becoming Wet?

The best thing you can do to prevent air filters from becoming wet is regular HVAC maintenance. Properly maintaining the system can help you avoid the most common causes of damp air filters.

READ MORE: 10 Ways to Improve Indoor Air Quality