Humidity Control Tips

 

Humidity is the amount of water evaporated into your air. Prolonged levels above 60% will cause mold and dust mites.

In this article I have included information on humidity problems, it also includes helpful humidity control tips. This information is based on almost two decades of investigations of such problems in South Florida. For information on the Paston Effect check out this article.

If you are looking for help with a humidity problem, we at A Accredited Mold Inspection Service provide humidity investigations and mold inspections in South East Florida.

 

USE YOUR AC UNIT TO DETER A POTENTIAL HUMIDITY PROBLEM

Please use your AC on a regular basis so your air is cool and dry. For most people around this area that is between 74F and 77F. Up North the indoor average temperature is going to be a little colder. For humidity levels something above 50%RH and just below 60%RH is typical for Florida homes and not a problem.  Here is some additional info on normal indoor humidity levels. 

 

 

SET YOUR THERMOSTAT FOR HUMIDITY PROBLEM CONTROL 

If your property is in a humid area, then make sure the thermostats’ fan control is set to auto and not to on. This AC control setting is extremely important in humid environments. Your thermostat can be set to the ON SETTING in dryer climates and moderate climates but not in tropical and sub-tropical areas like Florida.

Why is an auto setting considered an important humidity control tip in humid areas? Auto setting causes the AC fan to deliver air only when the AC is cooling and drying that air, and this is good.
On the other hand, the on setting will allow the AC to deliver air even when the AC is not cooling and drying that air. So, when using the on setting the AC will sometimes accidentally pull in outdoor air, attic air, or wall cavity air and dump it into your building when that warm humid air has not been cooled and dried.

 

WHAT DOES THE BELOW FLORIDA SOLAR ENERGY CENTER CHART SHOW? 

The below table of results are derived from AC unit experiments that were conducted by the Florida Solar Energy Center. The chart shows that if you set your thermostat setting to the ON SETTING it will increase your humidity. This is obviously bad if you have problems with high humidity. Your humidity will be about 10% higher if you set your thermostat to ON than if you properly set it to auto.

 

 

 

WINDOW OR WALL MOUNTED AC UNITS AND NOISE

Do you have a noisy window unit AC? However, turning it off too often can cause humidity problems and mold. If the noise of a window unit AC bothers you when you are indoors, then set it to run hard and maintain a colder dryer environment when you are out for the day. This way you are not exposed to the noise as much. Sometimes it is possible to turn noisy window units off at night when you sleep if the temperature and humidity are not too high. If it is a very old unit, A newer window unit might be quieter and more efficient.

 

WINDOW OR WALL MOUNTED AC UNITS AND BUILDING PRESSURE

 

 

Here is an image from a property we did a humidity investigation on. At this property wet outdoor air was sucked into walls because of building pressurization problems. The negative indoor pressure pulled outdoor air into the walls. This creates a severe condensation and   humidity problem inside the walls. This pressure problem was created by a window mounted AC unit. If you have a window unit AC in a small guest house it may cause negative pressure in rare cases. I have seen it myself several times. I have documented it with smoke pens. And have seen the problem stop when the AC is shut off.

 

WHY DOES THIS HAPPEN?

This happens when the window or wall mounted unit is designed to pull a small amount of air out of the property and dump it outside.

This negative pressure can cause humid outdoor air to be sucked into the exterior walls in an uncontrolledly and un-intended method. When this outdoor air is sucked into the walls it will touch cold air-conditioned drywall. This condition will cause moisture stains in the shape of circles or halos around outlets and light switch cover plates. In the below photo the halo shaped moisture problem has been overgrown with mold.

This typically happens in small detached guest houses and pool houses located behind larger homes. 

The reason it happens on small homes is because the pressure change in a smaller property will be more pronounced. In a large house the pressure change will be buffered by the large area of air in the house.

 

WHAT IS THE END RESULT?

The interior of the walls will become full of hidden moisture and mold. I have seen the problem become very extreme at several times. The guest house will produce a very foul mold odor and will have to be gutted to get to all the mold.

If you have this problem the property will need to be gutted by a mold remediator, and the wall mounted AC will have to be replaced with one that does not create negative pressure. This does not happen with every guest house; it is a rare but severe problem.

Sometimes central AC units creates pressure problems if the AC ducts are leaking air, but to a much lesser extent. Strong overpowered kitchen vent hoods can also create pressure problems.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UPGRADING FROM A WINDOW OR WALL MOUNTED AC UNIT TO CENTRAL AIR

Central AC units are less noisy, and do a great job of controlling humidity when used on a regular basis. Therefore, if you upgrade to a central AC unit the noise should not be an issue.
One thing to look out for when switching from window units to a central AC system is proper AC size. If the central AC is too large for your property, then it will cool the property and shut off before it has a chance to dry the properties air. So, in conclusion, do not get an AC that is larger than it needs to be.

FRESH AIR INTAKES ON RESIDENTIAL AC UNITS

Residential AC units rarely have fresh air intakes. They look like a metal dryer vent duct inside or near the AC return area under the AC. The return is the area where air returns to the AC behind or near the filter.
A fresh air intake on a residential AC unit almost always results in an expensive mold disaster. Residential air handlers with fresh air intakes almost always cause severe humidity control problems, and humidity mold problems in homes.

Based on my personal observations, it is typically a very good idea to close and seal fresh air intakes that service residential AC units in hot humid climates. In dryer climates or when dealing with some AC unit that might be designed to handle excess outdoor air introduction, it might be fine. Each case has to be handled individually.

I did an inspection for an in-law, they had humidity problem related mold, so they moved. They did not ask for an inspection of the place they were moving into. Months later that called me out to the new property because it also had humidity problem related mold. That new property had a fresh air intake under a residential AC unit. I instructed them to close the intake and have the mold removed. The humidity problem went away and the mold never returned. In fact, I have done many inspections where residential fresh air intakes caused humidity control problems and surface mold.

 

FRESH AIR INTAKES AND PRESSURE IN COMMERCIAL BUILDINGS

Commercial buildings are often required to have positive pressure. Commercial buildings almost always have fresh air intakes that maintain positive pressure by introducing fresh outdoor air. The positive pressure is creating by pumping in extra air from outdoors.

This extra outdoor air dilutes fumes, and it also dilutes body odor produced by people in the building. The pressure created by the extra air also has the added benefit of pushing cool dry indoor air into the hollow walls. This is good, it is the opposite of what happens when a window unit AC creates negative pressure that pulls wet outdoor air into the walls. This all sounds great, and it usually is.

 

THE PROBLEM

However, positive pressure in a commercial building can create serious humidity problems. In humid environments, outdoor air is often wet and rainy. When you pull in the above referenced air, then it causes an overload of humidity in the AC unit and ducts. Next, this overload of humidity causes mold growth in the AC and ducts. Afterword, the humid air is dumped into the building, and this can cause mold to grow on building surfaces. This is made even worse if the AC unit thermostat is set to on and not to auto. If set to on then the AC pulls fresh air in from outside and often dumps it into the building when it is not first drying that air.

 

TIMERS ON COMMERCIAL AC UNITS

During commercial building inspections, I have witnessed a few severe humidity control problems where commercial building thermostats are wired to a timer that shuts the AC compressor off at night. If the compressor is off at night, it saves electricity. However, if the compressor is off at night, the AC does not cool and dry the air at night. In such cases, the AC fan may stay on even when the timer turns the compressor off. Thus, the fan will pull hot humid air in via the fresh air intake all night long, and the AC compressor and coils will have been shut off by the timer and thus, will be unable to facilitate the cooling and drying of this humid outdoor air.

 

In such cases employees complain of mold, odors, high humidity, and respiratory problems. The same employees will report that in the morning the building is extremely humid almost dripping wet. The reason is, the AC was not drying the air all night long when the timer turned the compressor off. The timer may have even turned the entire AC off all night long.

 

THERMOSTAT ON SETTING WITH COMMERCIAL AC UNITS

A nearly identical type of humidity problem occurs if the thermostat is set to the fan on setting in a commercial building. If the thermostat is set to fan on, then the AC fan will stay on even when the thermostat turns the compressor off. Thus, the fan will pull hot humid air in via the fresh air intake all night long, and all day long and the AC compressor and coils will be unable to facilitate the cooling and drying of this humid outdoor air because they we turn off at times.
In such cases employees complain of mold, odors, high humidity, and respiratory problems. The primary difference between a timer related humidity problem and a fan on setting related humidity problem is that the timer related on causes more severe problems in the night and morning.

Recommendations

In such cases, for humidity control, I recommend that:

1) The fresh air intakes be closed if allowed by local regulation.

2) The AC units or AC unit’s compressors should not be set to turn off at night.

3) And the thermostats should be set to auto and not to on.

 

 

WHAT ABOUT DEHUMIDIFIERS?

I typically don’t feel the need to recommend a dehumidifier. I have no problem with them, it is just that a properly working AC dose the job of humidity removal so most people do not need a dehumidifier. One may be very helpful for the control of humidity if you do not use your AC to remove humidity. A dehumidifier may also be helpful if the AC is too noisy, or does not work well. They are also great in humid basements and crawl spaces where no AC is present to dry the air.

 

Dehumidifiers that sell for a few hundred dollars are very effective at humidity removal in the 50 to 70 pints per day range. Some have a built-in pump to pump out the water they pull out of your air. I highly recommend you get a good dehumidifier with a build in condensate pump. The water they remove will build up in the reservoir until you empty it. If you fail to constantly empty the reservoir the unit will shut off to keep from overflowing. So, in conclusion, a build in pump is a big convenience.

 

A CASE STUDY

I did a humidity inspection for a multi-billionaire in the Fl keys. His name is Mr. None of your business. I recommended dehumidifiers in the guest houses. In addition, I recommended that they all be drained to the exterior or to drains. The reason they needed them was because of high humidity and widespread humidity mold in 6 guest houses on one oceanfront estate! I almost never recommend dehumidifiers because typically the problem can be corrected with a properly working central AC and limiting outdoor air infiltration. In this rare case the best solution was dehumidifiers. The property manager did get the dehumidifiers I recommends he get. 5 years later they called for a 2nd inspection. They had a real problem; the mold and humidity returned.

 

The reason the humidity issue returned is because the dehumidifiers had all filled up with water. This caused the unit’s safety switches to shut each dehumidifier off. Thus, the dehumidifiers were not doing anything to control the humidity problem. So, in conclusion, get dehumidifiers with built in condensate pumps, or drain the units to the exterior or to nearby drains. Or simply monitor and maintain your dehumidifiers and be sure to empty them on a regular basis.

STOP OUTDOOR AIR INFILTRATION

One of the most basic humidity control tips or recommendations I can give is to not let in excess outdoor air when it is warm or humid outside. People who are near the ocean, or in any humid area should close doors and windows when not in use. Fix any entrainment holes in AC closets.
It is extremely helpful to let outdoor air in, but only if you are not near the ocean, and only during the seasons when outdoor air is cool and dry.

 

REMOVE HUMAN ACTIVITY GENERATED HUMIDITY

Also, use your bathroom vent fan during and after showers. Use your stove top vent hood when cooking. Venting humidity to the outside will eliminate most indoor humidity sources. Warning, sometimes kitchen vent hoods, and even bathroom vent hoods do not remove humidity, they just pull it in and put it right back out into the same room. Sounds crazy but it is true and it is common. In such cases vent hoods will do nothing to remove humidity.

Vent bathroom and cooking generated humidity to the outdoors to maintain humidity below 60%.  If you vent excess humidity to the exterior, and you use a properly working AC, then humidity induced surface mold will not have the proper environment it needs.

 

PRACTICE WINTERTIME HUMIDITY CONTROL

Most people do not know this, but it is often important to use the AC unit ALL YEAR LONG in hot humid climates.  To most people it seems strange to turn an AC on for cooling in the winter. However, if you do not use your AC in the winter, you may create a problem. In warmer regions of the world your indoor air will become very humid from showers and cooking. Your air will get more and more humid all winter long without winter AC use. Each spring I conduct mold inspections where people have mold on furniture, and in closets, due to wintertime humidity. This occurs because they did not use the AC all winter long.

By late winter or early spring humidity induced mold will grow on your clothes if you don’t let in dry winter air or if you do not use your AC all winter. This condition that I have noticed to occur each winter and spring I like to call renters mold. It typically only happens in small rental apartments in our area because small properties have less cubic foot of indoor air to dilute humidity. This is not something I learned in a book, it is something I see in late winter and spring in South Florida each and every year.

 

WINTER RENTERS MOLD CONTROL TIPS

This problem only occurs in hot humid climates. To prevent this, use your AC in the winter, or occasionally let some dry winter air in by opening doors and windows. Open doors and windows on cool dry winter days. Do so only if it is safe to do so. You must guard against letting in rain, pests, and human or animal intruders.

 

 

HUMIDITY MOLD

Why so much concern about humidity indoors? We control humidity in order to prevent dust mites and and more importantly to control severe Humidity mold problems.  The mold is often a type of Pen Asp mold called Penicillium Chrysogenum. In homes it appears like a powdery white residue mostly visible on dark surfaces like dark clothes, shoes, and furniture etc.

It is usually seen on dark surfaces due to the contrasting colors of the white mold on the dark surfaces. In a petri dish the mold turns green over time. If allowed to grow in the home for an extended period of time, it sometimes turns from white to greenish. It will spread and cause allergy or asthma symptoms.

 

HUMIDITY CONTROL TIPS FOR COLD AND DRY CLIMATES 

In more temperate and dry areas of the world humidity levels below 60% humidity and even below 50% RH should be an easy goal to achieve.

Outdoor humidity levels can be extremely low year around in the desert. In cold areas outdoor humidity can sometimes be acceptable in the summer, and very low in the winter. In addition, in cold areas, home heaters will dry the indoor air out quite well.  However, in arid regions, and in cold areas, people may need a humidifier to raise humidity levels.

Keeping humidity levels too low, for example below around 25% or 35%RH more or less may cause health complaints such as dry mucous membranes. This condition can cause a sore throat, nose bleeds, dry chapped lips, and even make a person more susceptible to attack from cold viruses. Low indoor humidity levels will increase static electricity that can damage sensitive electronics.

Maintaining humidity levels above 25% to 35% during the winter or in arid desert regions of the world can be difficult and may require a humidifier. In dry or cold environments, a humidifier can be used to break up water into tiny droplets and aerosolize them. Humidifiers are prone to breeding mold and bacteria inside the water reservoir and other components. Such devices must be maintained in a clean state, free of dirt and microbial growth. Here we provide some information on that topic. 

 

CONCLUSION

In summary, some of the best humidity control advice is to not let in too much humid outdoor air if you are in a humid area. Vent excess bathroom and kitchen humidity to the exterior. Use a properly working AC to dry your air. Set your thermostat to auto and not to on. By doing all the above, then humidity induced surface mold will likely not have the proper environment it needs. Do all this, keep humidity below 60%, and you should not have to worry about humidity mold problems.

Article by Daryl Watters CIEC.
Hope this helps. For a mold or humidity consultant in South Florida visit our homepage.