To open or close my windows

January 30, 2013


Often our clients with mold problems are told that opening doors and windows improves indoor air quality because it dilutes pollutants. Well that is true if you want to dilute indoor air pollutants.

If it is humid outdoors, for example around 60%RH or higher, then opening doors and windows can very easily cause mold problems that far out ways the benefits of the influx of fresh outdoor air. Hot humid air is even more of a threat than cool humid air.

Humidity problems comes from outdoor humid air when doors and windows are open and it becomes a serious problem when the AC unit is not used on a regular basis to help dry the humidity from the air.
If doors and windows are open when the AC is in use, then some of that hot humid outdoor air that enters the property be dried by the AC but an AC unit cannot typically dry all the air entering the property and entering the AC unit. The humidity that is not dried will become condensed under these new cooler conditions especially inside the AC unit, this is because most fluid media including air condenses or becomes smaller when it is cooled. Because the hot humid air is now condensed inside the cold AC the humidity in that air squeezes closer together and this causes the humidity in that air to rise to an even higher level than it was when it was outside.

Simple quick answers that are always correct are few and far apart in regard to mold problem advice, but in most cases it is not advisable to open doors or windows for extended periods of time if it is above 60%RH outside. If the outdoor air is rain free, dry, and clean and you are safe from intruders climbing in your window then opening your window may be beneficial as it may let in fresh outdoor air and dilute your moldy indoor air.


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