Replacing gas furnace easily

[daveshoe]

I have an old furnace that is rather large--about 5 feet deep and 2 feet wide. These old furnaces typically have the hot and cold plenums on top of the furnace. The furnace is divided in two sections The "rear ' section contains the blower motor and filters, and the front contains the firebox, heat exchanger,and supply plenum.
A more modern furnace contains a blower beneath the firebox,and the return air system is built up from ductwork,and the installer makes up an external plenum which is cut in to the blower housing at the base of the furnace[on an upflow furnace]
My idea is so simple,it is one of those ideas that makes you think--why did I not think of this sooner? At first,I was just going to cut the old furnace in two,and use the rear air chamber as a filter box,but then it hit me. The new furnace was the same depth and four inches slimmer than the front half of the old one. It actually will fit INSIDE the old furnace cabinet!
All I had to do was gut completely the old cabinet. Leave the part of the cabinet intact that separates the supply and return air.A Mikata impact driver and 1/4, 5/16, and 3/8 hex drivers and about an hour and the deed is done. The hardest part was finding all the fastners that held in the old heat exchanger.Cut a hole in the new case at the rear [where the old blower entered the firebox area] and it is ready to install. cut a small access area for the gas pipe and wires and we are getting close. To fill in the gaps in the top plenum, metal stud channel was cut to fit one side,and slightly narrowed for the other side by cutting along its length and overlapping the pieces to the desired width--then riveting the split channel to a smaller profile.
I did all this without having to bend or fabricate any new sheet metal from scratch.
When you think of how much work it would take to make up new supply and return plenums and the cost involved,this is a system that you may want to try. My total cost was a good used furnace for $85 and stud channel for a few bucks,screws and rivets