Sealing Central Cooling & Heating Cabinets & Ducts

In, (John Bunting)wrote:

Is it just me, or is most duct tape sold inferior? Mine doesn't last on warm air duct joints on my forced-air gas furnace. These ducts are not that hot. I can hold my hand on the duct without discomfort. I end up using pure silicone caulk(rated to handle 400 degrees F.) because that is the only material that holds up. replied:

Our local electric utility does not permit duct tape on ducts in installations they finance. They require "mastic". This is a material that hardens like a cast used on a broken arm. Can be used with a fabric tape to bridge gaps.

Local building supply stores (Home Depot, etc.) don't carry it or know what it is. Have to get it from industrial supply distributors.

They say "mastic" is required because duct tape is not permanent.

They do not recommend silicone caulk.


+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++  replied:

Gray duct tape simply won't stay stuck to heating-A/C ducts or cabinetry. The mastic stuff somebody talked about is considered the best method, but it's a mess to use.

I've had good results with the metal foil tape A/C people use. Had to get it at an A/C or thermal supply. There are some brands that meet local code and some that don't. The ones that don't are a lot cheaper. The A/C supply house near me claims most servicemen who buy there use the cheaper non-code type, so that's what I use. So far, the cheap one's worked well for me.


Note: I have now read posts on saying some home centers sell a foil tape for less than $3 a roll. I doubt it's much good for this. When I say cheap above I mean $6-$8. The tape that met code ran $12 -$14 at an A/C supply place.


Your Minimum Daily Allowance of Trivia

Duct tape got its start during World War II. It was produced in 1942 for the U.S. Army as a water-proofer for ammunition cases by Johnson and Johnson Permacel Division. The soldiers found it to be extremely versatile and used it for everything from the intended purpose to repairing things like guns, jeeps and aircraft. Due to its waterproof nature, it was quickly dubbed "duck tape."

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