Humidification 101: Why Humidify?
Many homeowners realize that they live in a “sick house” in winter months.
Proper home humidification reduces static electricity, revitalizes dry skin and soothes scratchy throats. It adds moisture to dry, cracked furniture, and wilting houseplants. It protects valuable artwork, antiques, and musical instruments. It even saves money on winter heating bills. That’s because properly humidified air feels warmer, allowing you to turn your thermostat down a few degrees.
Humidity and Relative Humidity
All air contains moisture, called humidity. It is invisible, except when the air’s saturation point is reached and the moisture condenses. Then, we see humidity as steam, fog, rain, or water droplets. The term relative humidity [RH] refers to the percentage of water vapor present in the air at a given temperature. For example, at 50 percent RH, the air is holding half of the moisture it’s capable of holding. The air’s capacity to hold water decreases as the temperature goes down, and increases as the temperature goes up.
How Temperature Affects Humidity
On a hot, humid day water droplets form on the outside of a glass of ice water. The droplets do not come from the water inside the glass. Rather, the cold surface of the glass cools then surrounding air and lowers its capacity to hold water vapor. The excess moisture condenses on the outside of the glass. Furnaces often create the opposite effect in your customers’ homes.
On a crisp winter day, the weatherman may report that the outside temperature is 30°F with 90 percent humidity. When the air infiltrates a home and is heated to 72°F, it expands ton four or five times its previous size. While the amount of moisture remains the same, the amount of humidity relative to the air volume [the RH] is reduced from 90 percent to approximately 19 percent. That’s why homes
are noticeably drier in winter, which damages woodwork and valuable possessions, and leaves residents feeling uncomfortable and, in some instances, unhealthy.
House Ratings Defined
Tight House – Insulated walls and ceilings; vapor barriers; weather stripping on doors and windows; snug doors, windows and fireplace damper. One-half air change per hour.
Average House – Insulated walls and ceilings; vapor barriers; loose doors, windows and fireplace damper. One air change per hour.
Loose House – No insulation, storm doors, storm windows, weather stripping or vapor barriers. Two air changes per hour.