"Does mastic produce any kind of odor that the air would blow out into the rooms?"

Yes. It uses hydrocarbons as a solvent.
It will stink till it dries, then smell again when the heat comes on and dries it out more.
It will eventually stop.
Why can't you put the mastic on the outside and slide the flex over?
Use some nitrile gloves if you want to stay clean.

Thanks for the answer. I kinda figured this was true, but wanted the confirmation before I began using the outside-method.

It's ok for me to put it on the outside. What I was thinking of doing is applying the mastic to all supply boots first (as opposed to one at a time as you're attaching the boot).

That way I could set them all up and have my assistant [fancy word for my wife ;) ] do all of the flex duct connections while I worked on something else.

It's just more of a pain for me 'cause I can't really multi-task during duct installation.

Thanks again,
Shade

I used small amounts of it on the inside of my fiberglass plenum whan I connected other ducts to it and never smelled anything - Initially or during the first heating system. The plenum itself (a fairly complicated piece because I had moved the furnace to one side by about 18 inches) was professionally assembled at a local HVAC shop and they used some on the inside as well. The owner of the shop told me what to buy and where to get it

I'm no expert at ductwork and I wanted to make sure I had a solid, leakproof system so I glued everything everywhere I could ;-)

It all came out very well and I saved a ton of money

Don

I apply the mastic to the exterior, use Hardcast Irongrip
brand. You can apply it with a paint brush, but I rarely do this..gloves- hands in tub of mastic so I can apply a heavy coat & feel it seal all seams.
But then I also seal corners of supply plenum, return plenum, junction of plenums to heatingsystem/coil/air handler..depends on install. I also seal corners of supply boxes, & take off collars @ plenum. Then I seal the supply boxes to the attic floor.

My work achieves the 5% duct leakage requirement for Energy Star. It has taken a lot of testing to find out just where these leakage areas are...well a lot of work to
get the hvac co to do this...I usually either do it myself
or oversee work being done.

Worth the extra effort (imho)...and I never use ductboard anywhere except to seal return air chase..but that is just me! When I do use ductboard in the chase/return I use a mastic tape...again Hardcast Mastic tape.

Best of luck to you!

Ductboard shines in unconditioned spaces.
The lower mass reduces the amount of heat that can be absorbed by the material and this reduces the load on the system when it cycles on.