duct insulation

[EdT]

My son and I a redoing an old house he bought from FMAC. The HVAC ductwork is all metal, and it is insulated on the outside with foil-faced fiberglass that was, when new, probably about 1" thick. It is all fastened to the ducts with miles of baling wire wrapped over the outside of the insulation. Surprisingly, in some of the calmer parts of the house, the insulation is in pretty good shape, but in other areas where it got wet it is rather nappy and falling apart. My question is, is there any reason NOT to use foil faced rigid insulation to re- insulate the portions of the ducts and plenums that are rectangular in cross section. It just seems tidier and easier than the foil faced batts and more readily available than the rigid duct board which is hard for the DIY dilettante to buy in reasonable quantities. I did buy a small roll of foil faced batt at HD, but it was really ****. The foil was not bonded to the glass and it was pretty pricey to boot. Thoughts?

 

[mrobins297aaa]

If your talking about foil faced rigid fiberglass insulation, I can't think of any, make sure its fastened good with something more than tape or it'll fall off. You can use drill screws with fender washers in a few thought out places.
Duro dyne makes a peel and stick pin that sticks real well to clean sheetmetal
it has a push on washer to hold the insulation.
also get some of that silver tape for the corners, they sell it at home depot.
see the attached picks

 

[EdT]

Actually I was thinking more along the lines of foil faced isocyanurate foam (the yellowish stuff) that is often used for wall insulation. The suggestion of the screws/pins to hold it on is a good one in either case. I've not been successful in finding reasonable sized sheets of the rigid fiberglass board in my area. About the biggest that I have found is 2'x4' and that won't go very far. Shipping is a big issue with anything like a 4'x8' sheet.

 

[wolftrucking]

Check out A comercial building supply house like U S Gypsum distributors that services contractors. They know thier products and depending on how much and how often you buy you might be able to get a contractor rate especialy if you are doing a rehab. I try to stay away from home centers most are clueless. Living in western N.Y. any insulation on your duct work is a good thing as your HVAC system wont have to work quite as hard, will be more efficient, and may last longer. Also, consider a vapor barrier like Tyvek it breathes to let out moisture but will protect from drafts especialy in a crawl space, mobile home, or if for some reason you have air flowing where your ducting is located.

 

[trbomax]

If your talking about foil faced rigid fiberglass insulation, I can't think of any, make sure its fastened good with something more than tape or it'll fall off. You can use drill screws with fender washers in a few thought out places.
Duro dyne makes a peel and stick pin that sticks real well to clean sheetmetal
it has a push on washer to hold the insulation.
also get some of that silver tape for the corners, they sell it at home depot.
see the attached picks

This is how i insulated my plenums.I used urethane adhesive as well as the fender washers.

 

[mrobins297aaa]

Actually I was thinking more along the lines of foil faced isocyanurate foam (the yellowish stuff) that is often used for wall insulation. The suggestion of the screws/pins to hold it on is a good one in either case. I've not been successful in finding reasonable sized sheets of the rigid fiberglass board in my area. About the biggest that I have found is 2'x4' and that won't go very far. Shipping is a big issue with anything like a 4'x8' sheet.

I would think it would be ok, I would check with the manufacturer just to see what he may have to say.
the last time I bought some of that rigid insulation from the supply house it was $38 per 4'x10'sheet, so almost $1 sq/ft, it does make a nice job.
actually what I used was duct board, its a little more dense.