Evaporative Coolers for Arid Climates and Mold

Cesar Collado
March 17, 2020

Reading Time: 6 minutes

What About Swamp Coolers (i.e. Evaporative Coolers) and Other Portable HVAC Units? Mold is Especially an Issue for These Common Systems?

By Cesar Collado

While centralized HVAC systems have become standard in homebuilding since the 1970s, there are a significant portion of homes that use evaporative coolers, window AC systems, or mini-split systems.  These systems require a level of maintenance that is much greater than Central HVAC due to the nature of the systems and physics involved.  Since these are considered appliances of sorts, regular maintenance is required, but often overlooked.  This leads to mold problems!  Mold sensitive patients should understand these HVAC systems.  They can be very cost effective and optimal for many housing units in the right climates.  However, their construction, wet conditions, and exposure to dust make them mold spreading machines. Read more about Evaporative “Swamp” Cooling

Single units are often burdened with cooling larger areas without duct work to distribute the air. Thus, they work harder and longer.  Because of that, water condensation can accumulate in collection pans, around the system installation, or as a result of snow and freezing in the case of outside exposure.   Since almost 50 Million of the 139 Million housing units (homes and apartments) do not have centralized HVAC, it is important to talk about how moisture and mold impacts these homes. In addition, evaporative coolers are less complex and do not have a rigid maintenance schedule to follow.   These appliance companies are different than HVAC companies and are not financially incented to advertise and pursue these calls.  As a result, there is a cognitive bias that makes people believe they shouldn’t stop working or need maintenance.  This applies to all small appliances like coffee makers, washers, and dryers.

Evaporative “Swamp” Cooling

Throughout much of the Rocky Mountain Regions and the dryer, hot climates of the Southwest, swamp coolers have not lost their effectiveness.  The principles behind these coolers dates back to the ancient Egyptians where manual fanning over water jugs were used to cool homes.  This evolved into hanging wet blankets across doors, and later in Persian “wind-catcher” systems that caught wind via a gentle sloping aqueduct and pushed the air into buildings.  Our bodies follow the same principles when we sweat.  In these climates, low humidity makes swamp coolers very cost effective and efficient.  In dry climates, adding water vapor to air is welcome adding moisture for occupant’s health as well as preventing woods from drying too much.

Swamp Coolers are simple machines consisting of a blower fan, a water line,  pump, and absorbent pads that hold water so that the air can be filtered through them for cooling.  They are highly effective in hot and dry climates; however, they simply do not work in any areas where humidity runs high.  They are extremely energy efficient when compared to refrigerated air and do not contain refrigerants that can be harmful to the environment.

Evaporative Coolers for Arid Climates and Mold

After some research I learned that when you ask about the origin of “swamp” Cooler name, the most common answer you’ll hear is the fact that if a swamp cooler isn’t regularly cleaned, it’ll begin to smell like a swamp.

Swamp coolers require a labor-intensive maintenance process to clean mold that accumulates as a result of the moisture combined with dust. Accumulation of mold is normal with a belt driven fan pushing air  through a cellulose pad that remains wet.  The blower effectively distributes mold into the home! They must be cleaned inside and out at least 3-4 times per year, even though they are often winterized or shut down during the winter.  Each time they are cleaned, a person needs to have all appropriate safety precautions (gloves, eye protection, mask, and Tyrek safety suit or fully protective clothing), as disrupting minimal amounts of mold can release millions of spores into the air.  The cooler must be semi-dismantled to expose all working parts that must be cleaned and scrubbed with soap and an antimicrobial product.  Bleach is often used effectively with metal equipment; but be cautious to avoid mixing bleach with any other product.  Read more about mixing bleach dangers HERE.

Evaporative Coolers for Arid Climates and Mold

The inside of a swamp cooler promotes mold growth. The pads are made to absorb and hold water.  These are often made of cellulose material.  Aspen wood shavings are the most popular for their cooling efficiency.  These wood shavings, combined with water, result in eventual mold growth.

Evaporative Coolers for Arid Climates and Mold

Window AC , Mini-Split Systems, and Hotel AC Units

Swamp coolers are ineffective in humid environments, which leads to the question about East and West Coast, Mid-Atlantic and the South.  With Central AC available, why do many buildings still have window AC units?

This answer is simple.  Residential buildings that were built prior to the advent of central air conditioning are not equipped with ductwork required to distribute the air.  If you take NY as an example, 75% of buildings were built prior to 1970. Many New York City’s buildings are historic and don’t have adequate spacing for airducts to pass through the walls.  There are exorbinant hidden costs to install central air.  These include breaking down the walls, to installing the ducts, remodeling, repainting.  Modern residential homes are built with floorplans that are designed with HVAC efficiency taken in consideration.

Window units require more than normal maintenance.  They should be monitored for mold as it often grows on the vents.  While the visible vents can be cleaned, there is likely mold accumulating in the interior of the unit.  These units work the same way all refrigerated air conditioning work by pulling warm air from the home, absorbing the heat and moisture from the air, and blowing cool air inside while blowing warm air outside. Refrigerated AC from windows also removes moisture from the air to maintain humidity levels.  Because the units are dark and warm inside, it can serve as an incubator for mold.

Maintenance to clean mold in a window unit is a bit more complicated.  It requires safety equipment, involves some disassembling, leather gloves to avoid getting cuts from the grill or coils, and some special tools to clean inside the grooves of the grills. Moisture can also accumulate on the outside of the unit resulting in moldy or rotting wood in the windowsill.

  1.       Wash the filter
  2.       Clean the fins
  3.       Straighten bent fins
  4.       Clean and vacuum the coils (use Leather Gloves to avoid injury)
  5.       Wash the fans and the pan
  6.       Store it properly in the off-season

It is important to note that there is a collection pan below the unit to collect condensation.  Ideally, the collection pan will be at an angle to drain water; however, most window units have flat pans.  They must be checked routinely and cleaned of mold.  Waiting until a scheduled maintenance could be costly for your health as mold is inevitable with still water and dust in the unit.

Mini-split or ductless AC units are a variation of the window unit, only they have an outdoor unit where the refrigerant dumps the heat pulled from the home.  These units have advanced where they can be designed for temperature zones, minor ductwork, or use multiple units in concert to cool an entire home.  These units use approximately 30% more energy than central AC.

Swabbing Air Conditioners

When faced with the appearance of possible mold coming from a portable air conditioner, window unit, or swamp cooler, ImmunoLytic’s swab tests are ideal.  The swab has a microfiber-like tip that collects proper sample amounts.  You can then send them off to be analyzed by the lab for detailed results and explanation.  You can purchase a 3 pack of these swabs accompanied by lab results on special HERE

Using an Evaporative Cooler in the Winter

One of the issues faced by all homeowners during the winter is dry air.  The common solution for many people is to use small room humidifiers or install whole home humidifiers. These tools, while immediately helpful, are very conducive to mold growth in the humidifier.  Whole home humidifiers can create systemic moisture problems throughout the home and lead to costly remediation and repair. This is especially important for the ~25% of people who are genetically predisposed to be sensitive to mold.

A portable evaporative AC can be very useful for homeowners.  Since the AC unit is meant to introduce humidity into the air and distribute it, short powerful periods (10-15 min) on with these units will distribute adequate moisture for health and comfort without the petri-like conditions homes can encounter with humidifiers.  These units can cost in the $100-200 range.  Since they are seldom used, mold isn’t an issue.  Using an evaporative cooler to increase humidity in short bursts where the interior and furnishing can dry accordingly is a cost-effective way for mold sufferers to deal with winter dryness in the air.