[Christ]

I have a 90% efficient home forced air heater, and I wanted to do a few things to it not only to get more of the heat into the house, but to use also some of the waste heat (from clearing combustion gases) for something else.

An idea I had for the duct work was taping all the seams, then using some cardboard corner/edge spacers and wrapping the duct with shrink wrap, leaving an air gap between the plastic and the metal of the piping.

The air coming upstairs isn't terrible hot, I think as long as I don't get too close to the actual heating unit, this will be OK. Anyone has any other suggestions? Keep in mind, its not my
house (yet), so I cant modify the heater in any extreme way.