Does anyone have a recommendation for sealing galvanized ductwork? I've read that mastic is the best, but looks like it might be a bit of a mess. Tape seems easier, but I've read that most don't perform very well. Any thoughts? What about a specific brand of tape that is approved by most building codes (UL-181) for use on metal ductwork? All I seem to find at most stores is UL-181 approved for ductboard or flex duct, not metal.

Thanks for any help,
Brian

hvac1000

If you want the tightest seal go with the mastic.

Covalence Adhesives - covalenceadhesives.com

For the best tape in the world. Once you put it on it will not come off.LOL No kidding. Look under hvac on there site.

bkspero

I've sealed mine with UL-181 aluminum tape about 18 months ago. No sign of loosening or leaks so far. One bit of advice. It's easy to puncture the tape with sharp edges of sheetmetal. Like where the ends of the "C" connectors bend over. Be prepared to put a few layers of tape over those areas. I dry wiped dust from the areas where the tape would be applied, but did not clean it with any fluid (the ducts are 18 yrs old).

LinfieldPA

Thanks for the replies. I picked up some Nashua 324A (Covalence Adhesives product). I had looked at it before, but it says "recommended for use on fiberglass air duct" and nowhere even in their literature do they even mention sheet metal duct. I figured they'd have one that was made for (or at least marketed towards) sheet metal ducts, but apparently not. I assume 324A (foil-backed acrylic adhesive) would be fine for sheet metal? What brand do/did you guys use?

hvac1000

Actually if you go to there wab site and look thru all the stuff they do have a tape specific for sheet metal. What you have may work.

I use POLYKEN 558CA tape for my metal work Nashua and Polyken are sister products so to speak. They are probably the best.

bkspero

I used two different products sold by Lowes. One sounds like the Nashua product you mention (for use on foil faced rigid fiberglass duct) and the other was heavier weight and slightly wider made for sheetmetal. I had to take greater care with the lighter weight tape for fiberglass ducts to avoid or patch pinholes from sharp edges on the ducts, and also to make sure that the slightly narrower tape bridged all the gaps with reasonable area for adhesion. But as far as function is concerned, I have seen no difference between the 2 after 1.5 heating and 1 cooling season. Both are sticking tightly to the ductwork.