Do Evaporative Coolers Cause Mold?

Homeowners are often concerned that their evaporative coolers may cause problems with mold or mildew. Fortunately, there are many steps that you can take to ensure that this does not occur.

Evaporative coolers do not cause mold or mildew to grow when they are used correctly. Routine maintenance can ensure that the machine’s moisture output follows the guidelines; this requires an understanding of how to maintain a balanced airflow in and out of the home.

Evaporative coolers are pretty straightforward to operate, and any mold or mildew issues should be resolved with some simple troubleshooting. There are a few common causes of mold or mildew in homes with evaporative coolers.

Do Evaporative Coolers Cause Mold?

Evaporative coolers make homes in dry and warm climates more comfortable by blowing out air that is cooler and having a humidity content adequate for raising the indoor humidity level to the desired target range of 45-55%.

The added humidity may promote mold or mildew growth, but this can be prevented with proper operation. Homeowners are encouraged to familiarize themselves with the optimal operating conditions for evaporative coolers.

How to Prevent Mold in an Evaporative Cooler

The growth of mold and mildew can be combated with a few routine maintenance steps, as you will see here. The key is to ensure that the equipment is kept clean and that any damages or leaks are taken care of right away. 

There are several common sources of mold and mildew that are identified below, along with tips on how to prevent these problems from occurring.

Use with the Appropriate Climate

Your local climate will dictate the usefulness of evaporative coolers. For example, in humid conditions, a swamp cooler will only exacerbate any mold or mildew problems that you are currently experiencing or have experienced in the past.

Evaporative coolers are most suitable for homes in dry and warm climates, as is seen in this map. You will notice that they are not recommended for anyone living in the eastern half of the United States. 

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Even in some of the areas where evaporative coolers are common, their use should be limited during certain times of the year when the outside air is more humid. Evaporative coolers become counterproductive as soon as the relative humidity outside your home reaches 60%.

You should avoid running your evaporative cooler during times of elevated humidity. In climates that are dry and warm, this may only be a seasonal weather event.

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For instance, Arizona and New Mexico experience seasonal monsoons during July and August that make conditions much less favorable for evaporative cooler use.

For the rest of the year, you should be able to operate your cooler free of mold or mildew concerns.

Replace Evaporative Media Pads 

Swamp coolers have evaporative media pads located within the cooler; this helps freshen the machine’s air.

With time, mold and mildew may accumulate on the evaporative media pad’s surface and cause a foul odor to be emitted.

The solution to this problem is to simply replace the media pads as needed. Instructions on how often you need to replace the evaporative media vary by model.

In the case of the more expensive single pad coolers like the Portacool Hurricane, it can be expected to last five years

Other swamp coolers may have aspen wood fiber pads, cellulose fiber media, or aluminum/plastic pads.

These media types are cheaper, but they may need to be replaced multiple times throughout a single season, depending upon how frequently you use your system. 

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Be sure to check the owner’s manual for your specific model for instructions concerning the evaporative pad’s replacement.

Routinely Check Water Levels

You can help prevent mold and mildew in your home by regularly checking the water levels inside your swamp cooler.

Too much or too little water can lead to problems. If there is too much water inside the cooler, then the moisture output will be too high; this can contribute to the growth of mold and mildew in the home. 

The water reservoir for any evaporative cooler should contain a marked line guiding how full the tank should be. 

Make Sure That the Water Reservoir Is Not Damaged

If the water tank for the evaporative cooler becomes cracked or damaged, it may begin to leak out water into your home; this can also contribute to the growth of mold or mildew in the home.

Any kind of damage will also contribute to a dip in performance quality. If you already have an evaporative cooler and notice that it hasn’t been working as well lately, a damaged water reservoir may be the culprit.

Homeowners are encouraged to regularly inspect the interior of their evaporative coolers for cracks or leaks. It is pretty simple to replace the distilled water reservoir on your own if you need to. Consult with the owner’s manual for your specific model for instructions on replacement. 

Clean the Water Tank Regularly 

A crucial component of routine maintenance activities includes cleaning out the water tank so that mold cannot grow inside the evaporative cooler.

If it is allowed to grow uncontrollably, the spores may be distributed throughout the home.

Manufacturers recommend that you empty the water tank at least once per week to prevent the accumulation of mineral deposits and mold. If you notice any mold or mildew, this would be a great time to knock out growth with a chemical treatment.

There is no need to get too complicated with your mold treatments. A simple white vinegar solution is adequate for killing out mold and mildew:

  1. Start by opening the drawing plug to remove any remaining water from the tank. 
  2. Then, scrub the inside to remove any debris or mold. 
  3. Allow a small amount of white vinegar to soak in the tank for a contact period of 1 hour.
  4. Then scrub and rinse once again at the end with water to remove the remaining vinegar residue.

Clean the Exterior of Your Evaporative Cooler

Since the evaporative cooler is continually drawing in air, it is also a magnet for all sorts of dust, grime, and pollen present in the air supply. 

These particulates can plug up the swamp cooler, causing it to behave less efficiently. They can also dirty the air supplied throughout the home.

This problem comes with a simple remedy: the routine cleaning of equipment. The exterior of the cooler should also be wiped down at least once every few weeks.

You can use warm water and mild soap to wipe down the surface of the evaporative cooler, as needed.

Air Flow Needs to Be Balanced

The air coming in and out of the home needs to be balanced while the evaporative cooler is being operated. If the airflow is allowed to become unbalanced, humid air will begin to accumulate inside the room. The humidity will contribute to the growth of mold and mildew along the house’s walls and ceilings.

To prevent the buildup of humidity, you should either install air ducts in each room or open the windows slightly while the evaporative cooler is in use. For homeowners who don’t use their evaporative cooler all that often, cracking the window during use may be the easiest way to go.

Installing air ducts for use with your evaporative cooling system is not that arduous of a task, though. If you don’t want to have to pry your windows open any, you can install up-ducts in the ceiling of your home. Up-ducts function by venting warm air into the attic, while the evaporative cooler releases more comfortable air into the house.

Take Advantage of Your Exhaust Fans

Regardless of whether you have an evaporative cooler, you should be taking full advantage of the exhaust fans in your home. 

The goal is to maintain an indoor relative humidity of 45-55%.  Any less than that and your skin will feel dry and chapped. If the humidity is higher than the target range, your home will become susceptible to mold and mildew.

A big part of achieving the target range humidity level within your home is to use the exhaust fans when the shower is in use. A steamy shower without ventilation will defeat any efforts to control the humidity inside your home. 

Periodically Run the Evaporative Cooler on Fan-Only Mode

Periodically operating the evaporative cooler on the fan-only mode will help clear out any built-up mold or mildew, particularly when it comes time to stow the cooler away for the offseason. Otherwise, you may be given an unwelcome surprise when it comes time to pull the evaporative cooler out for the next season.

The fan-only mode shuts off the water pump while keeping the fans running; this allows ample opportunity for the cooler’s interior components to dry out completely. You may also consider doing this during times of low demand during the season of use. 

Daily operation of the water pumps does not provide much of a chance for the cooler’s interior components to dry out.

Final Thoughts

While evaporative coolers can cause mold growth, homeowners can easily prevent it using the tips discussed above. As long as you keep the cooler’s components clean, replace parts as needed, allow ventilation, and use it in the right conditions, you should face little to no mold and mildew issues.

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