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Chicago Mold Inspection Indoor Humidity Information
Humidity control in homes is just as important as temperature control. In the Winter it is usually necessary to add moisture to the air, and in the Summer moisture needs to be removed. Moisture levels in the air are measured as Relative Humidity : the amount of moisture in the air as compared with the maximum amount that the air could contain at the same temperature, expressed as a percentage. A Hygrometer is used to measure relative humidity.
Humidification
Moisture usaully needs to be added to the air of a home in the Winter. In an average home, normal air infiltration around doors and windows completely replaces inside air about once every two hours. Heating this outside air to room temperature (70°) will reduce its relative humidity. Use the chart to calculate how much it will drop.
Outdoor/Indoor Relative Humidity Conversion Chart
| example : | Outdoor Relative Humidity 60% Outdoor Air Temperature 30° Warming outdoor air to 70° reduces relative humidity to 14% |
Wintertime relative humidity inside the average home hovers around 15%. By contrast, the average humidity in the Sahara Desert is 25%. Some of the results of low humidity levels :
- Dry Skin
- Chapped lips
- Clogged sinuses
- Shrinking, cracking woodwork
- Wallpaper peeling
- Static electricity
- Air temperatures feel colder
Adding moisture is normally done with a Humidifier. Humidifiers can be self-contained units (free-standing console, through-wall mounted or under floor mounted), or connected to a heating and cooling system (powered unit or bypass unit). The humidifier should be controlled by a Humidistat, normally it's a manual humidistat which is set to a specific % relative humidity level.
Too Much It is possible to have wintertime humidity levels too high. High humidity can cause :
- Condensation on windows
- Condensation in/on exterior walls
- Mold and fungus growth
- Swelling of woodwork
The lower the outside temperature, the lower indoor humidity needs to be to prevent condensation. Single-pane windows will have a much bigger problem with condensation than double-pane windows will. Condensation from windows or walls can cause damage and promote mold, don't let your humidity get too high
Causes / Sources of high wintertime humidity :
- Un-vented gas appliance
- Un-vented dryer
- Pool, hot-tub, shower
- Humidifier running too much
- Wet basement and or crawlspace
- House is too air tight
Add a humidifier to your forced-air heating system to put moisture in the air in the winter. If you don't have a forced-air system a self-contained humidifier can be installed, either through a wall or under the floor.
De-Humidification
Moisture needs to be removed from the air of a home in the Summertime. This is normally done by an air conditioner or de-humidifier. In either case the moistue is removed by drawing air across a cold evaporator coil, the air is cooled to it's dew point, water condenses on the coil and runs down a drain. An air conditioner can remove several gallons of water a day, de-humidifiers are rated in pints per day. Recommended humidity levels for Summer are between 50% and 60%.
Results of high summertime humidity :
- Promotes mold and fungus growth
- Swelling of woodwork
- Excessive rusting of appliances
- Physical discomfort
- Air temperatures feel hotter
Causes / Sources of humidity :
- Outside air infiltration
- Un-vented gas appliance
- Un-vented dryer
- Pool, hot-tub, shower
- Wet basement and or crawlspace
- Malfunctioning air conditioner
- Over-sized air conditioner (doesn't run long enough)
- Not warm enough for air conditioner to run enough or at all (commonly in Spring and Fall)
