Duct boot installation

Users who are viewing this thread

Lemmy

Member
Messages
56
Reaction score
0
Points
6
Location
knoxville, tn
I renovated a bathroom and the existing 2" x 10" HVAC register had to be moved to a different location. Previously it was just linoleum over the plywood subfloor and now it is tile on the ditra on the subfloor. The old hole in the subfloor was patched and a new one cut. However the duct boot was nailed to the subfloor in the old location using what appears to be 1-1/4 roofing nails. I have a few questions concerning installing to the new location.

How do I get nails in such a small opening (see attached picture)? Do I only nail on the short side which gives me much more room for a hammer? The old installation had nails on the long side but I am not sure how to do that.

The old installation wasn't sealed in any way, should I seal between the duct boot and subfloor using mastic tape, silicon, or something else?

Should the top of the duct boot be flush with the top of the subfloor (as shown in the picture), or should I bring it up to be flush with the tile? The tile doesn't come all the way out to the edge of the subfloor hole.

Thanks for any help.

ductboot.jpg
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
You absolutely should seal the duct boot to the subfloor (doesn't need to seal to the finish floor.) Duct mastic has better adhesion to different wood/metal/ceramic surfaces than most other sealing materials. Gaps bigger than ~1/4" may need mesh tape for support/reinforcement.

The seams of the duct boot need to be sealed with mastic too, even if they appear to be tight. Long straight seams in hard piped ducts & boots can be sealed with purpose made aluminum tape if it's all new-shiny stuff, but curved seams and dirtier or oxidized surfaces are easier to reliably seal with mastic.

Nail or screw the longer sides at an angle if need be, but be sure to air seal over the nails/screws, since vibration & time have a tendency to widen holes. Polyurethane caulk between the boot and wood can sometimes be used as an always-somewhat-flexible adhesive in lieu of or in addition to nails if the bite of the nail seems less than secure.
 

Lemmy

Member
Messages
56
Reaction score
0
Points
6
Location
knoxville, tn
Thanks! if I used the polyurethane caulk, would I still need the mastic to seal between the duct and the floor?
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
Yes, the duct mastic would usually be necessary. General purpose polyurethane caulk is an imperfect adhesive, but is better than construction adhesive in this application. If it's a really snug fit polyurethane alone might be enough- use your judgment. But it doesn't take much time to hit that seam with mastic for redundancy when air sealing the ductwork.
 
Last edited:

Lemmy

Member
Messages
56
Reaction score
0
Points
6
Location
knoxville, tn
Is there a preferred mastic and fiber tape brand/type? I was looking at the RCD brand but I'm a bit confused about which one to use. Design Polymerics 1030 is available locally so I might give that a try.

I've often wanted to seal all of my duct work, but during the fall/spring when the attic isn't miserable and I can go a day or two without needing to the run the system I often can't find the time. So I have no experience using mastic. If the gap is small (1/8 - 3/16 ) but is a flexible gap, will mastic still seal this well once it has hardened? I didn't know if the flexing could break the seal.
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
Most duct mastic is at least somewhat flexible and can accommodated the expansions/contractions of heating & cooling metal ducts. Some duct mastic (including DP 1030) uses fiberous reinforcement materials in the mix to ensure that it won't crack or separate even in high vibration locations. They're all pretty good at bonding well to different surface types- this as a mature type of product. I've seen ducts sealed with mastic 60 years ago still as tight as the day after it was applied.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks