Humidity creates all kinds of problems -- it promotes mold growth, makes wood swell and takes the crunch out of potato chips and soda crackers. Regulating humidity in a large space, such as your living room, is a job for an electric dehumidifier that circulates air through cooling coils to condense out the water. That's actually the main job of an air conditioner. For smaller spaces, you can save energy by making a passive dehumidifier with a desiccant, which is a chemical that adsorbs water molecules from the air. You can use good old table salt for this, but it probably isn't the best choice.
Some Common Desiccants
- Table salt -- If you don't believe that sodium chloride adsorbs moisture, try using your salt shaker in humid weather.
- Rice -- Uncooked rice is also a desiccant. It's a better desiccant than table salt, which is why putting a few grains of rice in your salt shaker keeps the salt flowing.
- Calcium chloride -- Calcium chloride is also a salt and aggressively adsorbs moisture from the air. It presents more of a health risk that sodium chloride, although that risk is still considered low. If inhaled, it can cause irritation of the lungs, and contact with the eyes or wet skin can cause irritations or burns. Because it's corrosive, it isn't a good choice for dehumidifying in spaces in which metal items are stored.
- Silica gel -- The little packets that come inside protective packaging are filled with silicon dioxide, or silicon gel. As long as silicon gel beads aren't coated with another compound, they are completely safe, and they can adsorb 40 percent of their weight in water.
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Saving the packets from products you buy instead of throwing them out gives you a ready supply of silica gel beads.
Making a Passive Dehumidifier
Whether you use rock salt, calcium chloride or silica gel, be prepared for the desiccant to shed water. Calcium chloride, in particular, eventually forms a solution with the water it adsorbs. To accommodate the water runoff, your dehumidifier should include a screen to hold the desiccant and a container to catch water.
Things You'll Need
Rubber bands or clips
Stretch a fiberglass screen across the mouth of a container. Your container can be a large one -- such as a gallon bucket -- or a small one, such as an empty juice can. Let the screen sag slightly into the opening and secure it to the rim with clips or rubber bands.
If your dehumidifier includes sodium chloride or calcium chloride, avoid using metal screening or a metal container. Both salts corrode metal.
Sprinkle the desiccant on the screen, making a layer that is 1 or 2 inches thick.
Cover the desiccant with more screen and secure the screen to the rim of the container. This prevents a spill if the container should be upended.
Place the dehumidifier in a closet, cupboard or drawer. Check it regularly and empty water or replenish the desiccant as needed.
Because it adsorbs water so well, calcium chloride is the preferred salt to use for dehumidifying. Silica gel is the material used in commercial products used in products sold in humid countries, such as Japan.