On Jun 24, 10:20 pm, "peter" wrote:
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?

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