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Will running the air conditioner in my home prevent mold or other problems in hot, humid climates?

By Christina Leon, Staff Writer

After months of paying high electricity bills I decided to purchase a stand alone air conditioner unit to place in my bedroom to see if it would possibly bring down the cost of monthly utility bill.  My concern was the possible increased risk of mold in my house that might be created by keeping the air conditioner at a higher temperature given that I live in sunny, humid South Florida.  I have known several people who after mold outbreaks in their home have had to vacate the house for months at a time, causing me concern at the possible risks of changing the temperature of my house.
Molds (and mildew) are fungi. Fungi are neither plant nor animal. The fungi kingdom includes edible mushrooms, the makers of the "miracle drug" penicillin and the yeast that makes our bread rise and our fine wines ferment. Biologically, all fungi have defined cell walls, lack chlorophyll and reproduce by means of spores. Approximately 100,000 species of fungi have been described and it is estimated that there are at least that many waiting to be discovered. The vast majority of fungi feed on dead or decaying organic matter. They are one of the principle agents responsible for the natural recycling of dead plant and animal life.
Mold has recently experienced a lot of press coverage due to the variety of inflammatory press reports concerning lawsuits over air quality in homes, courthouses and other buildings. In addition there have been parental concerns regarding school classroom environments; home insurers refusing to cover mold damage; and widely distributed news reports on so-called "toxic mold." All that said, it seems mold can be managed effectively in most cases.  The purpose of this article is to give clarity and insight in how to best prevent and be aware of mold.

There are four elements needed to create an optimal environment for mold growth: available mold spores, available mold food, appropriate temperatures and considerable moisture. The removal of any one of these items will prohibit mold growth. Mold is basically everywhere and so removing the availability of mold spores is impossible.  Mold spores eat anything but especially love paper, wood and organic fibers; the main items found in a living environment so reducing their food source is highly unlikely.  Regarding temperatures, mold grows in our refrigerators as well as hot tropical climates so finding a comfortable living environment that mold does not enjoy is practically impossible.  Moisture level is the component that can best be controlled and so is the variable this article will focus on to control the spread of mold.

How then can we reduce or eliminate the possible risk of mold in our homes?  This article is written concerning the climate found in South Florida and may not be applicable in other environments. 

 Air Conditioner Operation – Keep the air conditioner fan always set to “auto”  instead of in the “on” position.   When set to the “on” position the blower fan runs  continuously and the moisture which has condensed on your air conditioner's evaporator coil during cooling is re-evaporated and blown back into your home before it can drain off the coil and out of your home. This causes the relative humidity in your home to be significantly greater than if the air conditioner thermostat fan mode switch is set to the “auto” position.

 Air Conditioner Size - Air conditioner units are commonly oversized. The larger or  more oversized the unit the poorer it will be able to remove humidity. This is  because, during each air conditioning “on” cycle, the moisture removal does not  reach full capacity for about the first three minutes of operation. The more the system is oversized, the shorter the on-cycle during which moisture is removed. A home that is properly sized with a 2-ton air conditioner however has a 4-ton system is installed, the greater the risk of humidity build up.

 Thermostat Setting - Set the thermostat to the highest temperature that is  comfortable for you. A temperature of 78 F or greater is recommended. Do not try to  control humidity in your home via lowering thermostat as this will not work.  Two  things result from lowering the temperature in your home, first relative humidity  increases when the temperature decreases.  Second, lowering the temperature decreases the temperature of the materials in your walls, floors and ceilings of  your home, thereby significantly increasing the potential for actual moisture condensation on these elements of your home. A side benefit of setting your thermostat at higher temperatures is that it significantly decreases cooling energy  costs. This is exactly the news I was hoping to hear.

Some quick tips for maintaining comfortable living conditions and low cost solutions to the high cost of cooling:

 Ceiling fans are one way to keep your homes temperature higher, stay comfortable and  save money.
 Never leave windows open in hot, high humidity environments as this fosters mold   growth.
 Change air filters regularly and get professional service once a year to clean the   coils.
 Make sure sprinkler systems do not hit exterior walls of your home.
 Route exhaust fans (dryer) completely outside of home, not into any part of the   home.
 Minimize indoor house plants.

Mold in our homes can be a serious problem but as you have read, there are ways around this problem that are neither difficult nor costly to execute.  The unfortunate reality however is that once you have a mold problem, it then becomes quite costly and difficult to correct.