My crawl space is averaging 72% humidity right now (Raleigh, NC). I don't see any mold or mildew on the joists, the floor insulation is dry, and there is no condensation anywhere - EXCEPT the supply plenum (covered in condensation, soaked on bottom) and to lesser extent the return plenum. This isa recently installed system - performing well, indoor humidity steady at 45%). My tech says it's normal in a vented crawl. I am aware of dew points, etc , so I'm tend to agree with him. I plan to eventually close the vents, get a dehumidifier, upgrade the vapor barrier (doesn't current extend to the walls), etc., but until then:
- Will insulating the outside of the plenums help? (Tech says they are insulated inside already)
- Will it do any harm? (trap moisture between plenum and insulation, etc)?
- What type of insulation should I use? Where can get it?