How To Keep Mosquitoes Away From An Evaporative Cooler

Mosquitos are annoying and dangerous - and it is particularly problematic when they are breeding in the standing water of your evaporative cooler. So you are wondering, how do I keep mosquitoes away from my evaporative cooler? Well, you have found the right article. In this post, we gather up-to-date research to answer your question thoroughly.

There are several techniques for keeping mosquitoes away from your evaporative coolers (also known as swamp coolers). The techniques can be split into preventative techniques, physical barriers, and mosquito poisons. The main ways are as follows:

  • Preventative Techniques
    • Regular maintenance
    • Regular cleaning
    • Drain water often
    • Improve area's mosquito control
  • Physical Barriers
    • Screens
    • Nets
    • Sealing
  • Mosquito Poisons
    • Bacillus thuringensis products
    • Other water additives

Keep reading the rest of this post for details on each of the above bullet points and a quick intro on why mosquitoes like evaporative coolers in the first place. We will explain the steps required for each technique, why it is recommended, and, when appropriate, the downside of the technique. We conclude by answering several questions related to the topic of this post.

Mosquitoes gathering on the screen of the window, How To Keep Mosquitoes Away From An Evaporative Cooler

Mosquitoes and Evaporative Coolers

Mosquitoes love evaporative coolers because their larval stage occurs in standing water. All an adult mosquito needs is a small amount of water to lay its eggs. The larva then develops in that water, eventually emerging as adults.

Click here for an evaporative cooler from Amazon.

This means that the same appliance you use to keep your home more comfortable leads to a very uncomfortable living companion. In addition to the painful scratchy bites, mosquitoes are also carriers of many human diseases, including malaria, dengue, and yellow fever.

Keeping mosquitoes away from evaporative coolers is critical. For best results, combine preventive measures, physical barriers, and mosquito poison techniques.

Preventative Measures

These methods of keeping mosquitoes out of your swamp cooler are indirect preventative measures. The three techniques of regular maintenance, regular cleaning, and local mosquito control are also good standard practices no matter the mosquito situation in the evaporative cooler itself.

Regular Maintenance

Evaporative coolers are designed to use your tap water to cool air. If functioning correctly, there should only be minimal standing water. However, often water builds up in the bottoms of the evaporative coolers (this is common).

Regular maintenance and calibration help reduce the amount of extra water that flows through the system. That is to say; a perfectly calibrated evaporative cooler will only use as much water as it can evaporate. However, no evaporative cooler is perfect. That being said, if you hire out or perform all regular maintenance, you are less likely to have consistent standing water.

Regular Cleaning

Regular cleaning goes hand in hand with regular maintenance. Cleaning helps remove dirt and grime that the mosquito larva feeds on. Further, a messy evaporative cooler holding tank will retain more moisture than a clean one. This leads to reduced mosquito habitat.

Taking the time to clean your swamp cooler is a great idea, no matter the local mosquito population. Dirt and grime in your cooler are inevitably blown into your house. These air contaminants are usually harmless but can significantly aggravate asthma and other upper respiratory issues.

Read this great article from HVAC Seer to specifically learn about cleaning rust from your evaporative cooler: How To Remove Rust From An Evaporative Cooler.

Drain Water Often

If you are not using your evaporative cooler or notice water building up in the pan, drain it out. Ensuring that there is standing water in your cooler as short a time as possible will always help keep mosquitoes out of your cooler. Read this helpful HVAC Seer article to learn how to drain the water from your evaporative cooler: How To Drain Water From An Evaporative Cooler.

Improve Area's Mosquito Control

Taking the time to control mosquitoes in your yard and local standing water (such as ponds) will also help keep mosquitoes out of your cooler. Even more mundane techniques, such as tiki torches, can help drive mosquitoes away from your evaporative cooler's area.

Click here for citronella tiki torches from Amazon.

Physical Barriers

The theory of this section is that if the mosquito cannot access the water in the evaporative cooler, it cannot lay eggs there. For best results, combine screens, nets, and sealing as appropriate.


Mosquito nets are finely woven fabric that allows for airflow but has holes too small for mosquitoes to pass. Taking the time to drape or fix mosquito nets around your evaporative cooler can provide an effective barrier. However, these nets often leave small gaps around their edges that persistent mosquitoes will slip through.

Click here for mosquito netting from Amazon.

Further, nets will degrade over time. This inevitability requires that you regularly check the nets for any holes and repair those holes as needed.


Unlike nets, screens are more permanent and usually made of metal mesh or plastic. Also, screens typically last longer than nets. But in the same way as nets, screwing in or permanently affixing screens to the opening of your evaporative cooler will also keep mosquitoes out.

Click here for a roll of screen from Amazon.

After buying a screen that will not let mosquitoes through, cut the screen to the appropriate size. Generally, using sheet metal screws, you can then affix the screens to your evaporative cooler. Make sure you do not poke any holes in the actual blower assembly because this will reduce the unit's effectiveness. Like nets, screens might eventually fail over time and will require repair and replacement.


Click here for flex seal from Amazon.

Nets and screens work best in tandem with a well-sealed evaporative cooler. Inevitably, there will be small gaps in construction where mosquitoes can slip through. Using paint on flex seal and silicone caulk, paint all seams and caulk all wide gaps. This strategy will fill the small gaps in construction that mosquitoes will use to slip into your cooler.

Click here for silicon caulk from Amazon. This product requires a special caulk gun to use.

Gaps to pay particular attention to include corners and seams, places where water hoses enter or exit the cooler, and the edges of nets or screens. For a really solid screen seal, you can push the screen into undried caulk and then screw the screen into place. The caulk might be all the affixing material you will need to hold the screen for small-screened areas.

Mosquito Poisons

If you find that despite taking preventative measures and putting in place physical barriers. It is time to move to mosquito poisons. In short, you want a poison that is deadly to mosquitoes or mosquito larva but will not harm humans or pets when the evaporative cooler blows some of the chemical-containing water into the home.

Bacillus Thuringensis Products

Far and away, the most popular and safest ways of chemically removing mosquitoes from any standing water are Bacillus thuringensis (Bt) products. The most common of these are known as mosquito dunks, but there are other Bacillus thuringensis products on the market.

Click here for mosquito dunks from Amazon.

These products are composed of bacteria that are deadly to mosquitoes and mosquito larva but harmless to all mammals. Read this review of Bt from the National Pesticide Information Center to learn more.

Follow the directions on the mosquito dunk packaging to kill all mosquito larva in the standing water of your evaporative cooler.

Other Water Additives

Many sources also recommend other water additives such as essential oils. These natural products seem to work and are also commonly aerosolized to help bring pleasant odors to our home. This implies that using essential oils is also safe to keep mosquitoes out of your evaporative cooler.

Click here for peppermint essential oil from Amazon.

However, there is less known about the potential harm of this technique as compared to the well-established safe Bt. Use caution; this advice is especially pertinent if your household has anyone with an upper respiratory condition. To use, drop a few drops into standing water in your evaporative cooler.

How Do I Keep Mosquitoes Out of My Air-Conditioned House?

The best way to keep mosquitoes out of your air-conditioned house is to ensure that all home windows and doors remain either closed or screened. Mosquitoes can also enter through small gaps in construction, such as plumbing penetrations and other holes.

How Do I Permanently Get Rid of Mosquitoes?

This is a question that has likely plagued humans for centuries. There is no tried and true method of permanently removing all mosquitoes. Spending as much time indoors and in areas with lower mosquito populations are your best options.

If you cannot move, treating standing water with Bacillus thuringensis and spraying for mosquitoes will help keep local populations down.

In Closing

In this post, we answered the question of how to keep mosquitoes away from your evaporative cooler. This post covers all of the most common and easy-to-use techniques. To close, we answered a couple of related questions. Good luck!

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