Posted By PastTense on 27 Sep 2010 10:14 AM
Any experience with high capacity dehumidifiers? I have a 50 pint Walmart Energy Star dehumifier which runs continuously in my basement but still doesn't keep the humidity low enough (old house, lots of cracks...). So I am interested both in using less energy and keeping the humidity under better control--but these are expensive.
If your walls are not sealed and you have high outdoor dew points, you're basically trying to dehumidify the great outdoors. Air sealing the foundation, foundation sill, and rim joist, along with better backdraft controls on any clothes dryers, etc. as well as minimum sizing on any flue openings, etc can make a signficant difference in the infiltration rate.
In addition to air sealing, using silane-based masonry sealers on all foundation walls & slabs, can cementing all cracks big enough to get a knifepoint into can limit the ground moisture transport into the semi-conditioned basement. If you have a dirt floor, 10 mil poly vapor retarders are called for, mastic-sealed at the edges to the foundation (overlap 12" and mastic seal seams between multiple sheets where necessary.)
Unless you have regular bulk water intrusions, air transported moisture is by far the biggest factor raising humidity in a basement. If your eave overhangs are short and the foundation stays wet, providing for better drainage & splash-rejection on the above grade exterior counts too. (Masonry sealer above-grade, and foundation waterproofing below grade as well as a French drain along the drip line may all be necessary, if not sufficient.)
If the coolest part of the basement is kept below 60% relative humidity (monitor it!), you won't get much of that musty basement smell going as long as you keep all paper & wood off the cool basement floor.