How to Seal Existing Ducts In Crawl Space

[EddieWalker]

Is the water coming from inside the ducts? Condensation will form on the outside, not the inside.

If water is coming from inside the ducts, you need to figure out why and address that problem. They should be dry on the inside.

I like foil tape. It's kind of pricey, but it works great at sealing metal ducts. It's especialy nice to use in tight spaces and where you can't see what you are doing. Like the backs and bottoms of the ducts.

Once you get them sealed, then insulating them is a very good idea.

You might also price what it costs to buy flexible, insulated ducts and just replace what you have. If it's not a huge run, you might be better off with something new. I've done both, and replacing can be be much faster and more efficient then trying to get the insulation around those ducts in tight places.

Good luck,
Eddie

 

[dieselscout80]

Is the water coming from inside the ducts? Condensation will form on the outside, not the inside.

If water is coming from inside the ducts, you need to figure out why and address that problem. They should be dry on the inside.

I like foil tape. It's kind of pricey, but it works great at sealing metal ducts. It's especialy nice to use in tight spaces and where you can't see what you are doing. Like the backs and bottoms of the ducts.

Once you get them sealed, then insulating them is a very good idea.

You might also price what it costs to buy flexible, insulated ducts and just replace what you have. If it's not a huge run, you might be better off with something new. I've done both, and replacing can be be much faster and more efficient then trying to get the insulation around those ducts in tight places.

Good luck,
Eddie

Outside of the ducts only.

Most of the insulation is intact.

 

[dieselscout80]

You might also price what it costs to buy flexible, insulated ducts and just replace what you have.
Eddie

I was told not to use flex duct unless it was the only way due to the loss/resriction of air flow it this true.

 

[AHNC]

There are assorted types of duct seal and foil tape. If you have a nice tight seam, you can use a product like Polymer Adhesive's Airseal 11 or 22. Its like smooth peanut butter. If you have slight gaps you want something with a bit more body like the Airseal 33. It has a bit of fiber material in it to bridge gaps and hold together. You can get like products from other manuf like Hardcast. There are also materials with mastic and scrim tape. Kinda like sheetrock tape. Put some mastic down on the seam, overlay the scrim tape to tie it together and another layer of the goop. That system is very good, but time consuming. If you use tape you also want some scrim in the tape to hold it together. It is very awkward doing all this in a tight space. Once that is done you should probably use duct wrap to insulate. Depending upon the condition of the current duct it may be easiest to eliminate the existing insulation all together, evaluate/seal the system and do the duct wrap (vinyl covering over the fiberglass insulation) over the newly sealed ductwork. It makes a good looking package. And...check for mold and mildew in the duct. Your conditions are ideal for its growth. Good luck.

 

[PA hayseed]

There are assorted types of duct seal and foil tape. If you have a nice tight seam, you can use a product like Polymer Adhesive's Airseal 11 or 22. Its like smooth peanut butter. If you have slight gaps you want something with a bit more body like the Airseal 33. It has a bit of fiber material in it to bridge gaps and hold together. You can get like products from other manuf like Hardcast. There are also materials with mastic and scrim tape. Kinda like sheetrock tape. Put some mastic down on the seam, overlay the scrim tape to tie it together and another layer of the goop. That system is very good, but time consuming. If you use tape you also want some scrim in the tape to hold it together. It is very awkward doing all this in a tight space. Once that is done you should probably use duct wrap to insulate. Depending upon the condition of the current duct it may be easiest to eliminate the existing insulation all together, evaluate/seal the system and do the duct wrap (vinyl covering over the fiberglass insulation) over the newly sealed ductwork. It makes a good looking package. And...check for mold and mildew in the duct. Your conditions are ideal for its growth. Good luck.

Nice post.

I did mine, with some minor help from my brother who does HVAC work (guy comes over with some crimping tools and thinks he is running the show). We used foil on all the seams, wrapped it in bubble wrap (taping closed all spaces with foil tape again). We then made bands of bubble wrap and wrapped around the ductwork (to make an air space). Then we added a second layer of bubble wrap and taped all the seams with foil tape. We used double sided bubble wrap, and bought it in very large rolls (much cheaper).

In your case being in a crawl space, I don't know if it would work. Guess it depends on clearances you are working with. Mine was a basement, so plenty of work area, pluse we did it while installing.

Good luck with your project. I bet it will be a large PITA for you, or a contractor.

 

[PA hayseed]

AHNC, what about removing and using ductboard? I'm not an HVAC guy, but it comes at about r6.6, then he would just have to tape seams.

 

[Tig]

Condensation issues aside, I would suggest that duct tape is what you need.

 

[EddieWalker]

Do they still use Duct Tape on anything? I've never see it last more then a couple of years on anything. It drys out and the falls apart.

Foil Tape is more money, but ten times better!!!!

Eddie

 

[Tig]

I guess I'm just a Red Green fan.
There is lots of crappy tape out there that looks like duct tape. I know I don't have a decent roll on hand these days. I'm trying to think of an example of where real duct tape has stood the test of time for me........

 

[EddieWalker]

Don't think Gorrila tape is gonna be of any help. I have one roll of it and can't give it away. The last client that I left it with gave it back to me.

Eddie