Ductwork sealing

Paul B_5

What is the best Mastic /Tape /or whatever for sealing duckwork in an attic unheated space ... short of Foaming the whole works in.??? Paul

Brad White

Funny thing

Here in Massachusetts, according to our energy code, duct tape as we know it is specifically prohibited for use in sealing ducts...

I guess we are going to have to refer to it by it's second most useful function- Day Care/Babysitter Tape.

For duct sealing, I find the products by Hardcast company to be outstanding. Both their tape and activator system (FTA-20 I believe) and their 1402 Foil Grip tape is hard to beat. They also have a line of brush on sealants such as Iron Grip.

Not the only game in town but a very good product line.

Jack

There are several manufacturers

Polymer Adhesives is good. I like the Airseal 33 and 11. Kingco makes a good product and as all ready mentioned, Hardcast. I would recommend that you use a water based product regardless of brand. You don't want to get up in the attic and uncork some of the solvent based product because it will uncork you.

This is largely like putting spackling compound on sheetrock. Put a bit on, wrap the tape around the joint and mud it in. If you have fairly large gaps in the joint the Airseal 33/Kingco Glenkote (I don't know the Hardcast equiv)is probably the better way to go as it has a fiber component that bridges gaps a bit better.

Duct tape is useless after 30 days. In a hot attic, two weeks. Duct sealing is a good practice. It is required on commercial where they do pressure tests on duct systems. It should be SOP on residential also. I have a DOE circular that says you can loose up to 42% of your conditioned air in duct systems.

Paul B_5

thanks for the replies guys ...42% ouch!!!

hvacfreak

foil / butyl

http://www.hardcast.com/products/pdfs/TGM3300PDS.pdf

This stuff is just awesome. I've sealed small joints in medium pressure ( approx. 2.5" wc )duct while it was under pressure with this tape. The brand I used was Atco " Foilmastic " , I'm sure the Hardcast product is at least as good or better. The Hardcast description is right on target when it says " aggressive grip ".

Nick S

Actually, duct leakage can be, and often is much more than that.

Brad White

When you consider

that horsepower increases by the cube of volume, if you have even only 10 percent leakage it will cost you in rough terms a 30% increase in horsepower to recover that lost air volume by speeding up the fan.

Sealing ductwork is the work of the saints.

Mike T., Swampeast MO

While I don't recall the brand, the "best" mastic I've used is water-based, grey in color about the consistency of thinset mortar. Apply with a short, stiff bristle brush generously but not liberally to avoid too much of a mess.

With rectangular ductwork reapply into the corner between the drives and the esses BEFORE you carefully turn down the "just long enough" drives.

Remove the excess immediately (requires lots of rags and damp rags for the final cleanup) and cover ALL joints with a good quality aluminum "duct" tape. Cover ALL longitudinal joints in the straights and ALL joints in gored round fittings with tape as well.

If in unconditioned space carefully wrap with foil faced fiberglass insulation taking special care not to significantly compress the fiberglass and overlapping by precisely 50% in the straights and as close to such as possible at tees. Obviously you want such insulation to have 1/2 the value of the total value you desire. With the straight portion of round ducts you can perfectly wrap with 0% overlap but you really should seal the joints with aluminum "duct" tape taking especial care not to compress the fiberglass--now you want such insulation to have the full desired insulation value. The "double wrap" method somewhat less costly if somewhat more difficult to avoid compression...

For conditioned space wrap with bubble foil. While rather expensive on an R-value basis, it's relatively easy to install and providing you've sealed the underlying ductwork joints well, you'll wind up with very nicely sealed and very nicely insulated ductwork.

If "time is not money" and space is a premium you can get reasonable insulation of ductwork in unconditioned space by PERFECTLY cutting bubble foil to the ductwork, installing with contact cement on BOTH the bubble foil and the duct and sealing every joint in the bubble foil with aluminum duct tape. Just make sure that the ductwork contacts nothing EXCEPT other insulation.