Larry, that was a great write-up -- the beam clamps alone were worth the price of admission! I particularly like your trick of cutting a slot in the base of each clamp to accommodate the end of the cross-bar. I'm not sure, but these clamps may mean that I do not have to do any drilling into the frame members, which would be great.
And Old Biscuit, my furnace looks like it is made by Suburban, even though it says it is AirXcel. It is a model NT 16 SE. And peering into the guts of the furnace, it looks like there is a big round pre-cut hole in the side, covered by a round piece of metal. I bet that is a knock-out for ducting. Good call, and thanks!!
Now the dilemma -- it would take a lot of surgery to access that hole -- I would have to pull the furnace out and cut into a cabinet wall that currently supports my cooktop. I could probably put a "header" on the interior wall to redistribute the weight of the counter and the stove.
Then I would have to cut down into the subfloor to install the ducting to heat the underbelly. Not impossible, but not a minor project, either.
I guess it comes down to whether I want the furnace to heat the underside, or heat tape. My guess is that heat tape is easier to install (and would be more focused on the problem areas), and that would mean that I could run the heat tape off of electricity without the noise of the furnace. On the other hand, that means that I would have to have hookups to power the heat tape.
Life is a series of compromises.
