Madison Park

1. More insulation may make sense, but flex ducts are difficult to reinsulate.  I would first ensure that your ducts are not leaking at the connections.  Leaking air could be cooling the outside of the ducts and creating the cold surface for condensation.  

2.  Your condensation issues could also be related to the fact that you have excessive crawlspace ventilation -- too much warm, moist air entering the crawlspace.  Try to close a few dampers and see what happens.  The box fan idea also works when you it is less humid outside than in the crawlspace.  The same for the crawlspace vents.  Ideally, in our climate, they would automatically open and close depending on the ambient humidity...

3. You may also have excessive moisture from runoff and "sheet-flow" under your house.  Depending on how your house sits on grade, a french drain or sump pit may dramatically improve the humidity level under the house.  Our clay soils tend to direct water horizontally rather than vertically, especially when the soil is already water-logged.  

I installed a french drain at my house on the uphill side and it has dramatically dried out the crawlspace and backyard.  

Feel free to write me at anytime, I'm a commercial construction consultant and live on Wedgewood (not looking for business, just happy to advise).

shep.reynolds@gmail.com

I had about 25 feet of  large rectangular metal ducts under the house.  They use to be coated in puddles of water.  I did not wrap the old individual duct lines that were wrapped in a paper (probably back in the 1960's).    The metal ducts I had wrapped in a padded metallic insulation.  They were then taped and sealed.    It took care of the wet paper wrapped duct lines when those ducts were wrapped.   So that was good.     

It took 2 guys like 2 full days to do the work.

I also tried the french drain to keep the water from flowing under the house prior to doing anything.  My goal was to keep it drier under the house.   That helped some.  I forgot about that one until reading the post above.   

It is a bad problem for sure and understand your concern. 

I know my crawl space use to be so cold when it was so wet, it probably did have leaks in the ducts. 

My work I had  done was about  2 years ago, and I have been pleased with the results.  

Good luck whatever you try.  Sounds like Mr. Reynolds has some good ideas and knowledge. 

I just had some fencing installed last week and the guys dug down a couple feet and it was like hitting a pond.   Water everywhere under the topsoil.    

I just crawled my entire crawlspace again -- first time I'd had a thorough look since the new ducts were installed.  Most of the condensation seems to be near where two sections were spliced,  near where it's bunched up in the straps holding it to the floor joists, or near a few small tears in the shiny surface material.  They've not done the pressure test yet.  I imagine when they do, they'll find some additional work to be done.  

When I started this adventure, I didn't have gutters on the roof.  Everyone who's been down there has commented on how dry it is by the foundation at the front of the house.  Not what you'd call dusty, but from what I've been told, it's dry enough.  It was damp along the back wall, I installed gutters.  It's making a big difference.   

Humidity in the crawlspace compared to outside?  relative humidity is higher, but that's because it's cooler down there.  I used a quick on-line calculator and found the dewpoint is two degrees lower in the crawlspace than outside right now.  I think that tells me the crawlspace humidity is lower than outside?  So it makes sense to close the vents?  That might help get the relative humidity down below from 98 degrees, which might also reduce the amount of moisture available to condense on the ducts.

I'll do that -- close the vents, and fix the leaks they find when they do the pressure test on the ducts.  Then mop up, give it a few days, then have another look.  

I honestly never thought I'd be this familiar with my crawlspace.  

Thanks, everyone, for your advice.  I'll post again when I've done the above & see how it works out.

I meant...  down below 98%.  Relative humidity has been 98% down there all summer.