Originally posted by lit'l cat
Originally posted by teddy bear
With +90^F outside, air tight ducts, and a cold coil, you should be able to maintain 50%RH without a dehumidifier. Do you have a crawlspace with exposed earth or open outside vents? They are a big humidity load.
Teddy Bear,

I live in Richmond & have a crawl space (over a brick house) w/vents that I open in the summer time. It also has some plastic down but some spaces of earth are showing.

Should I close vents? I was always told open vents in summer & close in winter.
The old idea was that with exposed earth, open vents during the summer get rid of excess moisture evaporating from the expose earth. With vents open outside moisture entered the crawl but helped move out the earth moisture. Until the earth is well covered with plastic, closing vents will not help reduce the moisture level. After the earth is well covered with plastic, closing the vents stops the outside moisture from entering. Plastic covered, closed vents, and eliminating surface water makes humidity control easy. Maintaining <50%RH requires a reasonable amount of dehumdification. During cool rainy weather, 2,500 sq.ft. of home with a 2,500 sq.ft. crawlspace needs 100 pints of dehumidification to maintain <50%RH throughout. During hot weather the a/c may maintain <50%RH with little or no dehumidification.