Q. I have a finished basement (about 900 sq. ft), and I would like to improve the air quality and reduce humidity in the space. My dehumidifier runs 24/7 in the spring and summer months, and it produces a fair amount of heat that makes the basement uncomfortable in the summer. I’ve read some good things about systems like the WAVE or EZ Breathe. But I also understand that a system like that depends on the upstairs air being conditioned in the summer. Installing central air (which we currently don’t have) might not be incredibly expensive since we have a small ranch style house with an open attic. I don’t think that installing ductwork in the basement will be an option since the ceiling is sheetrocked. . . How do you suggest I best ventilate my house (including the basement)?
A. The primary source of the basement humidity is generated from the outside air infiltrating into the home. You also have to factor in the temperature difference in the basement. Cooler surfaces will form moisture on them (any surface below the dew point). Basements are generally cooler and therefore damper than the rest of the home. So how much water is actually being removed by your dehumidifier? Most small basements that are fairly air tight need 20-30 pints per day of dehumidification. High efficient, Santa Fe dehumidifiers can do this while generating 50,000 BTU’s of heat per day. Inefficient, conventional dehumidifiers can run 24/7 adding 100,000 BTU’s per day while not removing very much water. High humidity and warm temperatures are uncomfortable. So the more efficient dehumidifier will keep the space cooler and more comfortable.
The idea that you can remove the moisture in a basement by sucking the moisture loaded air outside the home is impossible. While removing the moist air from the basement, additional damp outside air is sucked into the home (the home is put under a negative pressure). The entire home will end up loaded with moist air. So what started as a basement humidity problem has now turned into a whole house humidity problem.
Get a good high efficiency dehumidifier like the Santa Fe Compact. Make the basement as air tight as you can and operate the dehumidifier to maintain your relative humidity down to 50%RH.
Regarding ventilation, close any open vents to control the amount of outside damp air infiltrating the space. You will also have natural ventilation through any imperfections in the home (any leaks and cracks). In most cases, unless the home has spray foam insulation throughout, natural ventilation is sufficient for the correct amount of fresh air.