correct way to seal leaky heating ducts?

The heating ducts come out of the furnace and into crawlspace. There, the joints are not sealed and leaks hot air.
The longest lasting way to seal these joints is to use hvac sealant, aluminum tape, or butyl tape?
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I've had good luck with aluminum tape................still holding since 1980.
Conditions SoCal crawlspace, galv duct...dusted & solvent wipe before tape.
Aluminum tape ithe the "peel off" backing paper.
Don't know about the other two products but 27 years seems pretty good.
YMMV
cheers Bob
I also used it on the water heater vent ........again still holding since 1980
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I've only used the metal tape. Love the stuff, just not when I cut myself on it. ;) As for mastic, I've seen professional hvac guys use it, messy stuff, and seems to have to cure before you can start the system.
tom @ www.FreeCreditCheckGuide.com
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