Ductwork wrap

ozone357

What wrap do you use and why. FSK Fiberglass or bubble wrap.

hvacfreak

itch

I just like the ..." warm , fuzzy feeling " I get from 1 1/2 and 2 inch fiberglass. I like mastic , staples , aluminum bands , thumb tacks , tape with knarley strings in it. When I start seeing " bubble wrap " with foil tape on 45 degree chilled water piping I'll sign on to that.

Brad White_185

Yo Yo Yo

Sorry, wrong rap

q:)

We specify 1.5-inch fiberglass with FSK for concealed areas and where in mechanical rooms, the same thickness in rigid board for supply ductwork.

For outside air ducts and plenums we use 2-inch, sometimes 3-inch thickness.

For the rigid board, we specify welded pins, not adhesive, taped joints with corner beads. Welded pins are also required on soft wrap where it spans over 24 inches below a duct, to prevent sag.

Bubble Rap? Lawrence Welk gettin' down with his own bad self? Not in my specs... what is the flame/smoke on that stuff?

mtfallsmikey

I thought

IMC required 2" insulation on trunk ducts.

Bob Bona_4

we use

or I should say "I" use 2" fiberglass (R6) for basement work, 3" (R8) for attic/truly unconditioned places. Energy code dictates.

The bubble wrap needs to be installed w/ spacers fastened to the duct (don't remember the thickness) to maintain air gap between the sheetmetal duct and the bubble to get the R value. The spacers are like bars or ribs spaced out 8" or so along the duct. Never done it, probably won't unless someone comes out with a less fussy material. Just think same principle as bubble under slab=no reflective=not so much R.

I just say no to ductboard in my resi arena.

Mark Hunt_4

We used

a two part spray foam. Seals the ductwork as you insulate and had a GREAT R-value.

Kinda' messy but much faster than wrapping and no itchy FG.

Mark H

Bob Bona_4

what did

the duct look like when you were done sprayin' Mark?

4 foot long white lumpy !@#$%?
Killing me here..thinking of the foam dripping on yer head, growing...:)

Mark Hunt_4

Surprisingly

it looked pretty uniform. Took a while to get the hang of spraying even layers, but once we did things looked decent.

One thing I found out quite by accident was that the foam actually protected the duct from damage. I was in a ceiling spraying some 24" x 8" duct and I slipped. I stepped on a section of duct that had been sprayed the day before and the foam did not flex a bit. I would not recommend jumping up and down on it, but if something was to fall on the coated duct, the chances of damage occurring are greatly reduced.

Never got it on my head Bob. But you are correct, you would look like the ugliest Chia pet in the world if you did.

Mark H

Brad White_185

It may well

and I will have to check.

For now, at least MA (where most of my work is), the real dictates are R value, not thickness.

(We have our own energy code and come to think of it our own bizarre way of looking at the world for that matter. But we will be an IBC state soon enough...)


We need at least R-5 where there is a 15 degree or greater delta-T between duct surface and ambient. If outside the building thermal envelope it goes to R-8. As a practical matter this corresponds to 1.5" and 2" although I would admit the 2" fiberglass can fall a bit short in that department.

Keeping in mind that these are minimums, we insulate anything with a 5 degree delta to ambient, where human contact is likely and where condensation is likely however remote. If ductwork is outside the building envelope for example, we specify (2) staggered layers of 1.5-inch board, the first fills the flanges, the second covers the gaps. Just one way anyway.

Josh_10

This stuff sounds interesting. Do you have a link possibly?

don_185

? Brad

Brad are you seeing any issue with sweaty duct inside the building envelope?

I know back in the day before houses became tighter and we did not have the dehumidifier feature/ colder coils that we have now.....that sweaty ducts inside the envelope was not
a problem.

What about that foam spray Mark speak of,does it not need a vapor barrier?

Brad White_186

No Sweat...

Hi Don-

You bring up a point not yet mentioned- Vapor Barriers!

All of the insulation in the world means bupkes when it comes to preventing condensation if you do not have a vapor barrier. And a poorly sealed vapor barrier is not a vapor barrier. (OK "retarder" for the persnickety...)

A good VB and you are in business.

As for Mark and Darin's foam system, that's the first I had heard of it. That it can be made smooth and presentable is to their credit- the stuff can be wild!

The key to that is the perm rating, the rate it can transmit moisture motivated by vapor pressure.

Closed cell foams have a higher perm rating than open cell. (Tiger Foam is an example of closed cell foams and this feature generally corresponds to the urethanes with R values in the range of 6.5 to 7.0 per inch. The open cell foams (Icynene being one, not that it comes in a DIY form) tend to have lower R values on the order of 3.4 per inch.

Key to perm rating is thickness and the literature for even the closed cell systems does not approach 1.0 (lower being better) until they get to 6 inches or so.

Point being, regardless of claims, I would wrap those ducts with foil/FSK and seal the rolled seams as well as possible.

My $0.02 anyway!

Brad