Originally Posted by Priusron
The furnace blows hot air into the belly through several holes in the duct. I can always open it up and remove the insulation. I hope with the flow of air through there it will carry off the moisture. I have read several forums and there was no good remedy that did not have negative consequences. 3/4 inch foam board with foil backing only has r-5 value. It would be difficult to get sheets into the middle area due to the ladder cross member. If I experience negative results, I will post them here.
I have never heard of wholes in your duct for heat in the underbelly, what TT do you have. Most units come with a 2" duct in the underbelly off the furnace. heated tanks and heated elbows take care of the other problem. There is some silver insulation on top of the underbelly which is about 1/4" thick with an
R value of 3.75. But can go up to R24. It is sold at HD and lowes in rolls mostly used to wrap water heaters but it is the same comes in widths up to 48".
It is sealed foiled front and back. Even if you have to double it you would never have a problem as Les brought up. Not cheap by any means. I will say this, if the factory cut wholes in my duct runs they would be replacing them.