Humidity Problems and Mold Growth

For help with mold or humidity problems visit our home page.

A Accredited Mold Inspection Service, Inc. Provides consultation, guidance, advice, and help with humidity related mold growth problems, and humidity problems in homes and commercial buildings throughout South East Florida including but not limited to Miami, The Florida Keys, Fort Lauderdale, Jupiter Island, and West Palm Beach as well as Palm Beach Fl. We have give corrective guidance pertaining to persistent  humidity issues with many oceanfront mansions.

Vislia humidity meter for reading humidity levels and detecting elevated humidity.

Vislia humidity meter for detecting elevated humidity.

Below is some humidity level information from Accredited Mold Inspection Service, Inc.

We are often asked what should I keep my indoor humidity levels at to deter mold growth ?

We all know that the AC unit should be used to help control humidity levels but some people believe it is 60%RH and others feel that it should be kept at 65%RH.

At A Accredited Mold Inspection Service, our specialty is dealing with mold and humidity problems in homes, and attics. Below we have compiled some information that may be helpful. 

This photo shows what can happen when humidity is not controlled.
Mold on a leather jacket from a moldy closet in a Lantana Florida home.
Photo taken by our inspector while conducting
an inspection for a local attorney.

U.S. E.P.A. (Environmental Protection Agency) on controlling relative humidity.  Keep indoor humidity low. If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity. Relative humidity can be measured with a moisture or humidity meter, a small, inexpensive ($10-$50) instrument available at many hardware stores.

U.S. E.P.A. (Environmental Protection Agency) “By controlling the relative humidity in a home, the growth of some sources of biological contamination can be minimized. A relative humidity of 30-50% is generally recommended for homes. Standing water, water-damaged materials, or wet surfaces also serve as a breeding ground for molds, mildews, bacteria, and insects. House dust mites, the source of one of the most powerful biological allergens, grow in damp warm environments.” Inspectors testing for mold in Miami or West Palm Beach should always look out for excessive dust because the combination of dust and humidity can easily lead to mold problems.





Cladosporium is the primary mold found on and inside AC units and duct. Here our humidity and mold consultant found Cladosporium and condensation on many AC registers.


When struggling with home humidity problem or other issues
related to elevated RH, or excessive moisture in your air, you must act swiftly. In humid buildings the resulting attic condensation and the resulting mold and mildew that often grows on clothes in closets can get out of hand quickly.


Well Known AC Manufacturer (Carrier) Your home comfort system should provide both comfortable temperatures and comfortable humidity levels. It should maintain your home at the recommended levels of 40-60% relative humidity, preventing growth of mold and mildew and minimizing dust-mites, bacteria and viruses.



ASHRAE Standard 55-1992 They make the rules for all AC contractors and AC engineers to follow. Thermal Environmental Conditions for Human Occupancy sets guidelines intended to achieve thermal conditions that at least 80% of the occupants would find comfortable. ASHRAE humidity levels are recommended between 25-60%.

Humidifier & dehumidifier sales and information website The optimum relative humidity level is generally considered to be between 40% and 50%. Levels anywhere between 30% and 60% is acceptable, however, below 50% is recommended to help control dust mites which are bad for allergy sufferers.

Well Known AC Manufacturer (Trane)
Most designers choose a dry-bulb temperature of 72°F to 76°F as the set point. To discourage microbial growth, ASHRAE Standard 62-1999 recommends a relative humidity of 60 percent or less during cooling. Therefore, select the dedicated AC unit to limit the relative humidity in all spaces to no more than 60 percent. Designing a dedicated ventilation system that limits the space relative humidity to a lower value (50 percent, for example) adds unnecessary cost because it requires larger equipment and increases energy consumption.

In South Florida mold on furniture in the absence of leaks is in most cases caused by a humidity problem. The white material on the desk is humidity related mold.

American Academy of Allergy Asthma & Immunology
To reduce dust mites, it is important to keep humidity below 50% throughout the home by using a dehumidifier or central or window air conditioning. Wall-to-wall carpeting should be removed as much as possible, especially if it is laid over concrete floors. Hardwood, tile or linoleum is better for people with allergies. Washable throw rugs may also be used if they are regularly washed in hot water or dry cleaned.

So why do some people recommend 65%RH? Well it appears that some older ASHRAE standards recommended humidity levels be lower that 65%, not 65% but lower than 65%. The newer ASHRAE Standard 55-1992 recommends levels between 25% and 60%RH. The recommendations for about 50% RH is probably related to the fact that dust mites in homes die if exposed to a RH of 50% or lower for a few weeks. The lower you keep humidity the higher your electric bill will be and 50%RH is not typically needed unless you have dust mite problems. Keeping humidity levels to low say below around 25% or 35%RH or so, more or less may cause health complaints such as dry mucous membranes and also may increase static electricity that is not healthy for sensitive electronics such as computers.

The following table of results comes from AC unit experiments that were conducted by the Florida Solar Energy Center. It  illustrates the relative humidity impacts of both thermostat set point temperature and the position of the air conditioner fan mode switch. (2)

What does it all mean? The chart shows that if you set your thermostat to on your humidity will be about 10% higher than if you properly set it to auto. During humid times the air conditioner thermostat should always be set to auto. Setting your thermostat to on in humid environments can cause a humidity problem.

Impact of Indoor Set Temperature and Fan Operation Mode
on Interior Relative Humidity*

Indoor   T

Avg   RH %
(Fan= Auto)

Run Time Fraction

Avg   RH%

















* AC operated alternatively for at least one week in each mode.

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Dade County Mold inspector in

Miami Aventura Miami Beach Coral Gables Coconut Grove

Monroe County Mold Testing in

Florida Keys Key largo Islamorada Marathon Key West

At A Accredited we offer commercial and residential humidity testing, and indoor air quality or IAQ testing as well as mold inspections in around and near all of Dade County including: Aventura, Hallandale, Hollywood, Miami, North Miami Beach, and South Beach. In addition we travel to Ft Lauderdale, Jupiter, West Palm Beach, and Boca Radon, in Broward, and Palm Beach County.

For Commercial, Long Distance, and Larger Mold Inspections All of Florida and the Caribbean.

Indoor humidity levels and mold growth  are a problem that our firm is familiar with, if you need help  with Indoor humidity problems and mold growth give us a call and schedule an inspection.

1 (888) 381-6651

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