Control of Indoor Humidity

Excess moisture in the air of your home not only affects your comfort and health, but can undermine the structural integrity of the house as well. High humidity promotes growth of microorganisms like molds, bacteria and viruses. Low humidity causes dries out respiratory linings, shrinks and warps wood and other materials, and causes cracking in walls and some flooring materials. That is why controlling humidity to the proper levels is so important.
But where does humidity inside a house come from? There are various sources:

- Soil moisture penetrating walls and floors of basements
- Outdoor air coming through cracks, holes and gaps in windows and door
- Ventilation
- Houseplants, aquariums and pets
- Cooking, bathing, cleaning and laundering
- Breathing of each household occupant releases about one pound per day of water into indoor air

Today’s energy efficient, tightly built homes tend to have problems with high humidity. They don’t have enough ways for indoor air to escape during hot summer months. Conversely, older houses which were built to “breathe” more, tend toward the dry end of the humidity range; during the winter, colder drier air comes into the house and is further dried by heating.

Best Humidity Range

For optimum comfort, humidity should be between 40 and 50 percent during summer and between 30 to 40 percent in winter. At those levels, condensation possibly damaging to materials is not present, and mold or mite growth is inhibited. Due to the fact that warm air rises, ceiling zones will be more humid than floor zones, and moisture levels will vary from room to room, but at the recommended humidity ranges, any extremes will be acceptable.

It is fairly easy to keep track of humidity levels by using a hygrometer. This is mechanical device in which a spring contracts or expands with changes in humidity; the spring is connected to an indicator needle which moves along a dial. Many indoor display thermometers incorporate a hygrometer in addition to the temperature measurement. There are also digital hygrometers, which operate electronically and are easier to read.

Dealing with Humidity Problems

What you do to get the humidity in the right ranges? There are several ways to go about it. Here are some tips for high humidity problems:

- Have proper ventilation
- Use an air conditioner in summer. Air conditioners actually cool the air by removing moisture from it.
- Limiting hot showers to short amounts of time will cut down on steam introduced into the environment
- Make sure your clothes dryer is properly vented to the outside, if not, use a clothesline to dry laundry outdoors
- Move large houseplants outdoors during warmer months
- When cooking food in pots, keep the lids on tight
- Mositureproof your basement

Here are some tips for dryness problems:

-Take longer hot showers and leave exhaust fans turned off
- Keep windows closed
- Add weatherstripping to doors and windows to prevent infiltration of dry outdoor air
- Simmer a pot of water on the stove (don’t leave it unattended, though)

Vapor barriers are installed in most newer homes; if yours does not have one, adding a vapor barrier can help control severe moisture conditions. A vapor barrier works by blocking the flow of air, which contains moisture, so it must be made of nonpermeable material.

Four to six mil thick sheets of polyethylene is the most common material. Other forms of barrier include Kraft paper, vapor retardant paint, glass, plywood and aluminum foil. Vapor barriers are placed behind walls, in upper floor ceilings, and over uninsulated floors.

Dehumidifiers and Humidifiers

If the passive methods of controlling humidity listed above are insufficient to overcome the dryness or moisture problems you have in your home, then a more active approach can be employed, with the aid of devices like dehumidifiers or humidifiers, or both. These are available as portable units that can be located as needed, and humidifiers are available as permanent add-ons to forced air heating systems.

For particularly humid weather, or drying out chronically moist areas of the home, dehumidifiers work well. Ratings for dehumidifiers are based on the amount of water in pints that the unit is capable of removing in twenty four hours for a given size room. For example, for a room that is continuously damp and musty and is 1,000 square feet, a good choice would be a dehumidifier capable of removing 17 pints per 24 hrs.

Another thing to look for when choosing a dehumidifier is the recommended minimum temperature. When operated in a room whose temperature is below 65 degrees, dehumidifiers generally will develop frost on them, which can damage it’s evaporator coils. Look for a unit with a frost control that will shut down the dehumidifier when frost forms, much like a thermostat. Some models even have built in coil defrosters to protect them.

A humidifier can help with an overly dry home. Smaller portable units are inexpensive and versatile, as they can be used in whatever room needs it, but the main disadvantage is that they must be continually refilled with water. A better choice is a central humidifier located in the heating system. Although they only operate while the heat or air conditioning is on, it is theses functions which are to blame for the majority of dryness problems anyway.