I've been diligently sealing up air leaks in the A/C duct work in our unfinished basement, using high quality heavy duty foil tape. I've sealed up everything I can get to. What I've now noticed is that most of the remaining leaking air is coming from the damper controls (I guess that's what they're called) on the sides of the duct work, especially those near the blower unit. (I've included a picture of a similar control to the ones I have, below, from the alibaba.com web site.) A significant amount of air leaks from the controls, and from the opposite side from the controls where the rod pokes through. I certainly don't want to plaster these things with foil tape, not only because it probably would be hard to make effective (since it's not a flat surface), but also of course because I want to leave easy access to the controls. I was wondering about using some sort of magnetic sheets or covers that could be applied over the controls (and easy to remove when needed), but am not sure what product would actually work well. Any suggestions? Thanks.
I would not worry about it. It is better to have the basement space conditioned along with the rest of the house, vs. not having it conditioned. Keeps the basement dry, air fresh, no bugs or mold.
I would be worrying more about going around the foundation and sealing any leaks from outside air, heat & cold from outside getting inside, along with insulating the Rim & sill's at the top of the foundation, where the top meets the floor for the first floor, than worrying about sealing a few minor leaks on your duct work.