Insulating furnace supply plenum?

[blueman]

Both the body of our high efficiency gas furnace and the ductwork seem to be quite well-insulated since they are at best slightly warm to the touch.

However, the sheet metal supply plenum coming out of the top of the furnace appears to be uninsulated and is relatively hot.

- Should this be insulated?

- If so what type of insulation? (I assume some type of rigid board but I imagine there could be code or safety issues given heat and proximity to furnace)

[hrhofmann]

Do you want heat in the basement, assuming that is where it is? If so, leave well enough alone, or have a building or home inspector check it out.