Winter Indoor Comfort and Relative Humidity
Compared to summer when the moisture content of the air (relative humidity) is an important factor of body discomfort, air moisture has a lesser effect on the human body during outdoor winter activities. But it is a big factor for winter indoor comfort because it has a direct bearing on health and energy consumption.
The colder the outdoor temperature, the more heat must be added indoors for body comfort. However, the heat that is added will cause a drying effect and lower the indoor relative humidity, unless an indoor moisture source is present.
While a room temperature between 71° and 77° F may be comfortable for short periods of time under very dry conditions, prolonged exposure to dry air has varying effects on the human body and usually causes discomfort. The moisture content of the air is important, and by increasing the relative humidity to above 50% within the above temperature range, 80% or more of all average dressed persons would feel comfortable.
See the table Apparent Temperature for the apparent temperatures for various combinations of room temperature and relative humidity. As an example of how to read the table, a room temperature of 70° F combined with a relative humidity of 10% feels like 64° F, but at 80% it feels like 71° F.
Although degrees of comfort vary with age, health, activity, clothing, and body characteristics, the following table can be used as a general guideline when raising the apparent temperature and the level of comfort through an increase in room moisture, rather than by an addition of heat to the room. This method of changing the apparent temperature can give the direct benefit of reducing heating costs because comfort can be maintained with a lower thermostat setting if moisture is added.