Yes, a swamp cooler can cause mold, but only when its water or its damp air ends up in the wrong place. It happens in three ways: shut windows while the cooler is on, a leaking roof unit, or a cooler that never got winterized.
How does a swamp cooler add moisture to your house?
A swamp cooler pulls outside air through wet pads. As the water evaporates, it cools the air by 15 to 40 degrees Fahrenheit. That figure comes from the Building America Solution Center, a Department of Energy program.
The cool air brings that water into your house with it. Direct evaporative coolers increase the humidity in the air, unlike a standard air conditioner, per Building America.
In dry Front Range air, that extra moisture is part of why a swamp cooler feels good. It turns into a mold problem when the damp air cannot get back out.
What happens if you use a swamp cooler with the windows closed?
A swamp cooler needs open windows or vents so air can leave the house. Doors or windows must be opened to give the air a path out, according to Building America.
It calls for 2 square feet of open window or vent for every 1,000 CFM of air the cooler delivers. With the house shut, the humidity climbs and the moisture settles on the coolest surfaces, like basement walls and cold water pipes.
The EPA recommends indoor humidity below 60 percent, ideally between 30 and 50 percent. A basic humidity meter shows you where your house lands on a hot afternoon with the cooler on.
Can a roof swamp cooler leak into your attic?
Yes. Roof-mounted systems are hard to reach for maintenance and can lead to leaks in the roof, Building America notes.
Water gets in when the pan overflows, a float valve sticks, a water line cracks, or the seal where the cooler meets the roof fails. It soaks the attic insulation, the roof boards and the top of the ceiling drywall.
The first sign is often a stain on the ceiling right under the cooler vent. If that stain has turned to dark spots, read our guide on how to get rid of mold on a ceiling.
What should you do with a swamp cooler in winter?
Shut it down before the first hard freeze. Building America lists three winter steps:
- Shut off the water line to the cooler.
- Drain the pan and clean it.
- Put a winter cover on the unit.
Close the damper or cover the cooler vent inside the house too, so warm house air does not rise into a cold duct. Building America gives the same advice for the ceiling relief vents a cooler uses: closed during the heating season.
In summer, empty the pan when the cooler will be idle for more than a few days. Standing water in the pan can breed bacteria and mosquitoes, Building America warns.
Why are swamp coolers so common on the Front Range?
Our summers are hot and dry. Evaporative coolers work best in dry climates where the outdoor humidity is low during the cooling season, per Building America.
That is why so many Front Range homes use one, often a roof unit on an older house. The same roof that supports the cooler also takes our spring snow and summer hail.
After a hailstorm, check the cooler cabinet and the seal where it meets the roof. A dent or a crack there can let water into the attic the next time the cooler fills.
When should you call about swamp cooler mold?
Call for help if you notice any of these:
- A stain, bubble or sag in the ceiling under the cooler vent.
- A musty smell the first time you turn the cooler on in spring.
- Dark spots on the roof boards or rafters around the cooler duct in the attic.
- Mold on walls or ceilings in rooms that were closed off while the cooler was on.
Fix the leak first. A roofer or a cooler technician should stop the water before any mold work starts.
In an attic, our team treats the mold with Anti-Microbial Dry Fog Treatment (ADFT), and attic jobs skip demolition. If water reached the ceiling drywall below, some of that drywall sometimes has to come out.
Send us photos of the ceiling, the attic around the duct and the cooler itself. We send back a number, usually the same business day. Our mold removal in Colorado page shows the rooms we treat and how we quote from photos.
Call (720) 443-4222 in the Denver area or (970) 469-9030 in Northern Colorado.