Question Duct Board

[CrealBilly]

Forced air system - can you use the space in between floor joists for duct, if you line the space with duct board?

http://www.certainteed.com/products/insulation/index/317382

 

[junquecol]

Yes. you can, but remember that duct board is about 1" thick, so you loose 2 inches of both height and width. To form duct board, you need special cutters. I have a set of such, both for the folds and for the laps that you are welcome to use if you would like. For return air, you can just use the space between the joist providing there isn't a piece of Romex running down it's length. Cats love to "sharpen" their claws on duct board, so any exposed has to be "cat proof."

 

[Glennbear]

Just MTCW here, invest in quality tape for your joints especially where you make your register drops. My first cooling season in this house I discovered that the builder was rather sloppy in sealing. :BangHead: The good tape will be UL rated for HVAC use as opposed to the universal grey junk. :wsmile:

 

[junquecol]

Just MTCW here, invest in quality tape for your joints especially where you make your register drops. My first cooling season in this house I discovered that the builder was rather sloppy in sealing. :BangHead: The good tape will be UL rated for HVAC use as opposed to the universal grey junk. :wsmile:

Tape for duct board will be metal foil, with a peel off backing, and fiber threads impregnated in it. It sticks great to ITSELF:wmad:!

 

[Gotcha6]

While others use duct board extensively, I've personally never been sold on the fact that the inner fiberglass strands don't flex and work their way loose and into the air stream over time. With the respiratory issues you've had with some wood dust, Jeff, I'd reconsider hard duct.

Nevertheless, it ain't my name on the mail box. :icon_thum

 

[JonT]

Tape for duct board will be metal foil, with a peel off backing, and fiber threads impregnated in it. It sticks great to ITSELF:wmad:!

Not to mention hair. Ask me how I know.

The right way to use ductboard is with mastic and fiber-strand tape. Adhesive "Duct Tape" (regardless of rating) will fall off, eventually. Same goes for the aluminum tape. Mastic is slow, messy and annoying but it's code and it lasts. Tape on ductwork is a guaranteed service call.

As for working with ductboard, the jobbers sell all sort of special angle-cutting knives for cutting bending angles, but I just use a razor knife with the blade set to cut about 80% of the way through. Plan your folds, use a marking crayon (I like yellow) and scribe a line down the middle of the fold line. Cut @ 45 degrees to each side of the line. fold. Done. If you do it right, the foil on the outside won't even be scored. Practice on some scrap, you'll get the hang of it quick.

Wear a fiberglass-rated mask or respirator while cutting. And gloves unless you like being itchy.