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Humidistat What is it? Do I need it?

This is a common question we get during a home inspection, "What is that dial next to the Thermostat?"

It is a Humidistat. To simplify it is a sensor designed to control humidity in a home. In our opinion it should always be left in the on position or bypassed. I'll explain why.

In cold climates the humidistat is used to control a whole house humidifier attached to the forced air heat system. It senses the humidity level traveling through the vents and tells the humidifier to add moisture to the air to get to a comfortable humidity level. Cool Right?

In warm climates with high humidity it is designed to save money by not running the A/C system until humidity reaches a set level. Many seasonal residents to Florida have them in their homes and condos and figure no need to run the A/C when I'm gone for the summer. Saves money right?

He lies the problem Seldom are these humidistats accurate to the exact setting on the dial they can be off by as much as 10%-20%.

Problem in cool climates with this is if you put excess warm moisture into the air and it's cool outside you get condensation on windows and exterior walls. Moisture in these areas leads to mold mildew and shorted life of the windows and building materials.

Problem in warm climates is if you set this to maintain 60% humidity and leave it won't allow the A/C to run until it senses 60% humidity (Remember these can be off by as much as 20% = a setting of 80% humidity. In Florida thats like turning your A/C off and leaving the windows one in the middle of the summer. Not only that but the indoor temperature could be 95 degrees and the A/C wouldn't run until the humidistat got to the specified setting.

Many types of mold thrive in humidity levels above 60% and below 30%. So if the humidistat is used it could easily lead to a mold problem very quickly especially in tropical and humid climates.

Mold Testing Air Quality Naples Fort Myers SWFL Home Inspections

Most HVAC companies will bypass humidistats when a new system or thermostat is installed. If your's is still connected in Florida I recommend setting the humidistat to the"ON" position this will allow the thermostat to control the temperature and humidity in the unit. thermostats are best set between 76 and 78 degrees when you are away.

If you have questions on settings please contact us or an HVAC company. Always have a trusted home watch company check your home when you are away. If an A/C unit fails in the summer in only takes a matter of days for mold to begin to form.

Southwest Florida Home Inspections preforms all types of home inspections and testing for home buyers, owners, and builders. We service all of SW Florida including Ft. Myers, Naples, Bonita Springs, Cape Coral, Estero, Sanibel and Marco Island. We hold all required state licenses including Home Inspector, Mold Assessor, and Radon Measurement Technician. We are fully insured for all services provided. We preform mold and radon testing in house additional more specialized tests are available and can be scheduled trough us with a professional specific to those tests such as lead based paint testing, Chinese drywall testing and WDO / Termite inspections. All inspections are conducted in a timely and professional manner with some reports available with in hours of completing the inspection. We are interNachi certified, IAQ2 Certified, NORMI Trained providing you with the knowledge and professionalism to minimize your risk of investment when purchasing a home, condo, or any other type of property in South west Florida.

Please Call, text or email us at 239-994-5810 or

We are here to help you through your inspection process and answer any questions you have before, during and after the inspection.

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