About two years ago we moved into a 35 year old house. The furnace
was replace by the previous owners and is about 10 years old (92+
Rheem). The ductwork appears to be original (except for a few pieces
around the furnace)
A problem we've had last year (and this year too), is that when the
weather cools down, the upstairs is about 5-7 degrees cooler than the
downstairs. Partially closing the downstairs registers helps some,
but I don't want to close too much and reduce the airflow through the
furnace to a level that will cause problems. I'm looking for a
solution to help the heat make it to the upstairs, without causing
problems with the furnace.
In the basement, above the furnace is the sheet metal plenum. There's
a couple of short 6" ducts that run out of this to the rooms directly
above. Off one side of the plenum, extending most of the basement, is
a long (15 feet), rectangular duct, about 20" wide by 14" high;
basically an extension of the plenum. The round ducts for the rest of
the house feed out of this at various points along it's length.
When the furnace is running, you can feel the heat radiating off of
the sheet metal of the plenum "extension". To me this is heat that is
being lost from going to the rest of the house. I was wondering if it
would help to cover this with insulation, and if so, what type? Rigid
foam sheets seem like they would be the easiest, but is that the best
solution? Also, should I just insulate the long extension, or the
plenum on top of the furnace itself?
Any suggestions would be appreciated.