Florida’s muggy summers can cause problems in a closed-up house. Plus, oceanfront or lakefront homes, or homes in low-lying areas with heavy tree cover, can be especially humid. When the indoor relative humidity (RH) exceeds about 65 percent, mold can start growing. There’s several different ways to keep humidity down while you’re away for the season:

1. A humidistat, which responds to changes in indoor relative humidity instead of temperature, is the first way to prevent mold. You can have an a/c contractor install one next to your home’s thermostat, and set it to override the thermostat when you are away for the season. Set the controls of your humidistat to 60 percent RH to maintain acceptable humidity and allow some leeway for any inaccuracy of the sensor. Shown below is an older, stand-along humidiat and a newer digital thermostat with built-in humidistat
2. If you don’t want to invest in a humidistat, another way to control mold when you’re away is by setting the air conditioner thermostat to around 78º to 80º F, with the fan set at “auto.” While it requires no additional investment, using the thermostat to control humidity is less energy efficient than a humidistat. It would also be a good idea to invest in an inexpensive (less than $10) analog hygrometer to verify that you a/c system is adequately lowering the humidity. A digital thermometer/hygrometer is another way to keep tabs on the indoor humidity and costs $12 to $20.
   
3. And last, the most economical way to prevent mold in a vacant home is by using stand-alone dehumidifiers instead of your central air conditioner. The rule of thumb is one for every 1,000 square feet. This option, however,  requires the most additional investment. 

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  To learn more about heating and air conditioning systems, see these other blog posts:

• How can I find out the SEER of my air conditioner? 

• My air conditioner won't turn on. What's wrong? 

• How can I find out the size of my air conditioner? 

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning? 

• What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• Why is my air conditioner not cooling enough? 

• What are the most common problems with wall/window air conditioners?  

• Will closing doors reduce my heating and cooling costs? 

    Visit our HEATING AND AIR CONDITIONING and MOLD, LEAD AND OTHER CONTAMINANTS pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.