How to deal with dampness
High humidity in the summer can be uncomfortable, and musty odors in a bathroom or basement are annoying. But humidity should be kept in check for more serious reasons, too. First, there's your health: excess moisture encourages the growth of mold and dust mites, which are known to trigger asthma attacks and cause nasal irritation, sneezing, and other respiratory discomfort. Humidity can also lead to structural problems in your home, including warped and rotten wood. It also encourages unwanted guests: rats, mice, and wood-devouring carpenter ants and termites thrive in dampness. High humidity can even boost your utility bill in summer, for the simple reason that humidity makes you feel warmer, encouraging you to crank up the air conditioner.
The higher the humidity in your house, the harder it is for water to evaporate from your skin. That's why humidity makes you feel warm in the summer. Water vapor can also make your basement or crawl spaces musty. Since it's a lot cooler down there, a lot more water will condense because the cool air won't hold as much water.
The ideal humidity inside your home is around 45%. Over 50% seriously encourages growth of molds and bacteria. If any part of your home is significantly higher than 45%, you should take the steps below and, if you still have a problem, consider a dehumidifier. On the other hand, letting humidity drop below 30% in living areas can cause other problems. For more about this, see our article on humidifiers.
Many problems with excess humidity can be eliminated or greatly reduced by taking the following simple steps to stop moisture at the source.
- Seal cracks in basement walls and foundations. Cracks obviously admit moisture. Look for them and seal them with a high-quality concrete sealer. Where there is general dampness rather than leaks, the application of a waterproof coating on the concrete may help.
- Check plumbing. Look for leaks, but also wrap any cold-water and drainage pipes where you see condensation forming. Also look for openings where pipes come through walls and floors and seal them with a good caulk.
- Clean and seal gutters and downspouts. Much of the moisture in basements comes from water that soaks into the ground close to the building. The first line of defense is to make sure there are no leaks or clogs in the gutters and downspouts. Once the water reaches ground level, it should be routed at least three feet away from the house.
- Add underground drains? Serious drainage problems may require installation of underground drainpipes close to the foundation. If you already have such a drainage system, run water through it periodically to make sure it isn't plugged. If the water backs up, you need to unclog the system.
- Use a properly sized fan in your bathroom.
- Use a range hood fan in your kitchen when cooking.
When shopping, look for
- Energy savings. The energy efficiency of a dehumidifier is measured by its energy factor, the volume of water (in liters) removed per kilowatt-hour of energy consumed. A higher energy factor means a more efficient machine. A hard-working dehumidifier can consume around $150 worth of electricity a year, so look for one with the EPA's Energy Star label.
- Easy-to-read, easy-to-set controls. Many models have electronic controls--some with digital displays--that allow you to set the humidity where you want it. If yours doesn't have such controls, you can purchase a hygrometer, which will measure your humidity. (These cost about $20.)
- The right size. Consider the size of the area that needs to be dehumidified and how damp the area is. A moderately damp 2,000-square-foot basement, for instance, will need a dehumidifier with capacity of 22 pints a day. An extremely damp area of the same size may need one that can wring out 40 pints a day. To cope with serious humidity problems in large crawl spaces, you may want to take a look at companies that provide more heavy-duty dehumidifiers specifically designed for crawl spaces.
- Easy maintenance. Most dehumidifiers have a water tank inside that must be periodically emptied. Some machines expect you to do it, and others do it automatically by draining into a basement drain or sump-pump cavity or pumping the water outside. If you are likely to forget to empty the water, then be sure to select one of the automatic machines. If, on the other hand, there isn't a convenient outlet for an automatic to drain to, make sure the tank is easy to remove and carry. You'll probably also want a washable air filter that can be easily cleaned.
- The right model for your climate. Many dehumidifiers operate best at temperatures above 65ºF. If the temperature of the area being dehumidified will routinely fall below that temperature, you should probably buy a dehumidifier designed to handle the cold--or one that shuts off if the temperature goes too low. Below 65ºF, frost can collect on the machine's condensing coils, interfering with its operation (just as frost does in a refrigerator). If you see frost on the coils, turn off the unit and let it defrost before starting it up again.
- As suggested above, you should shoot for an indoor humidity of 45%. But what does that really mean? Well, remember that notion that air can hold different amounts of water vapor at different temperatures--more when it's hot than when it's cold? That 45% figure refers to "relative humidity," the percentage of water vapor in the air compared with the maximum amount the air can hold at any given temperature. When the relative humidity reaches 100%, water condenses out of the air. This is why it appears as dew on the grass at night, or collects on windows during cold weather.
- A dehumidifier works on the same principle as a refrigerator with the door open. Coils inside cool the air. Because cold air can hold less water than warm air, this causes moisture to condense into the dehumidifier's tank.
- For the most efficient operation, close doors and windows when the dehumidifier is operating. No need to spend your hard-earned cash drying up the great outdoors.
A level of humidity around 45% is more comfortable and is better for your health. It's especially important for people with allergies or respiratory problems.
...to your wallet
Because a dehumidifier can protect your home from moisture damage, it can save on costly repairs.
...to the Earth
Depending on your climate and comfort level, a dehumidifier might even cut your use of energy for air conditioning, which would reduce your emissions of global warming gases. And, of course, wherever the device prevents damages to your home, it saves on resources needed for repairs.
The June 2008 issue of Consumer Reports has a thorough guide to dehumidifiers, showing which are the quietest, most efficient, and economical. Look for promotional sales in late spring and early summer, when the new models are unveiled.