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Weather > Winter Indoor Comfort and Relative Humidity

Effects of Dry Air on the Body

Studies have shown that dry air has four main effects on the human body:

Breathing dry air is a potential health hazard which can cause such respiratory ailments as asthma, bronchitis, sinusitis, and nosebleeds, or general dehydration since body fluids are depleted during respiration.
Skin moisture evaporation can cause skin irritations and eye itching.
Irritative effects, such as static electricity which causes mild shocks when metal is touched, are common when the air moisture is low.
The “apparent temperature” of the air is lower than what the thermometer indicates, and the body “feels” colder.

These problems can be reduced by simply increasing the indoor relative humidity. This can be done through use of humidifiers, vaporizers, steam generators, sources such as large pans, or water containers made of porous ceramics. Even wet towels or water in a bathtub will be of some help. The lower the room temperature the easier the relative humidity can be brought to its desired level. A relative humidity indicator (hygrometer) may be of assistance in determining the humidity in the house.

Referring to item 4, a more detailed discussion is necessary. While the indoor temperature as read from a thermometer may be 75° F, the apparent temperature (what it feels like) may be warmer or colder depending on the moisture content of the air. Apparent temperature can vary as much as 8° F within a relative humidity range of 10 to 80 percent (these limits are generally possible in a closed room). Because of evaporation the human body cools when exposed to dry air, and the sense of coldness increases as the humidity decreases. With a room temperature of 70° F, for example, a person will feel colder in a dry room than in a moist room; this is especially noticeable when entering a dry room after bathing.

For example, an apparent comfortable temperature can be maintained with a thermostat setting of 75° F with 20% relative humidity or with a 70° F setting with 80 percent humidity. A relative humidity of 20 percent is common for homes without a humidifier during winter in the northern United States.

Winter Indoor Comfort and Relative Humidity

Apparent Temperature for Values of Room Temperature and Relative Humidity