My house was built on a hill, and under the house on the lowest part of the hill, there is a 13'*28' unfinished basement. No HVAC, accessible only via an outside door, and we use it only for storage. Since we're in north Florida, the basement has a really nasty humidity problem, and anything down there winds up rusty or soggy. Life expectancy of a screwdriver bit down there: 1 year.

The house's HVAC ductwork is in the attic, so tapping that directly to run it into the basement is more or less out of the question.

I had the following thought, and I'd like to hear if it's a good--or stupid--idea:

- Cut hole in floor of HVAC closet and put floor air register in floor.
- Use a rectangular-to-round adapter, and run 4" semi-rigid metal duct through the crawlspace to the basement--about a 10' run.
- At basement, install directional damper, duct booster fan, and ceiling diffuser.

Thus, the booster fan would draw in conditioned/non-humid air from the interior of the HVAC closet [vicariously from the house via the grille in the closet door] and use that air to control the humidity in the basement.

The only issue I could see is that, when the air handler runs and is sucking air up, that it would be competing against the duct booster fan. The workaround I had in mind was to put an airstat in the air handler's intake, so that when the air handler runs, the basement duct booster fan stops--and the directional damper would close the duct.