[acsnowrider]

Would like to replace 20 year old furnace listed above, model # 867.766131/NDGG100DF02, to the newer 92% efficient CLOSE system furnaces. Does anyone know of a furnace/manufacture who builds one that will sit on my current base/plentum? Thanks John

[NorthernHeat]

I'd need to know the demensions. Any furnace will work, you may need to pan of the plenum or coil box it sits on. Widths of furnaces change based on BTU and manufacturer. Is your Hiel furnace an 80+ or natural draft. If its 70% you will go to a 75,000 90+. If it's a 80+ you will put in a 90,000 BTU 90+. Hope this helps.

[acsnowrider]

It's a old "flue" stle stack, rated at 100000 BTU (in 1985) and the base diamentions are 29" long x 20.5" wide. Furnace measurements are 27.75" long x 18.5" wide x 48" tall. The downdraft hole is 11.75" from the front, and measures 14.50" long, and 16.50" wide. I'm figuring that a 90,000 BTU rating would probably be enough, based on the newer ratings and efficient burn box designs And thank-you for the assistance John

[NorthernHeat]

A 100,000 BTU natural draft furnace has aproximatly 72,000 BTU output. A new 90% efficient 75,000 BTU furnace will have an out put of 69,000 BTU. The difference of 3000 BTU will never be noticed. The furnace will run longer each cycle at most. But this is good. A furnace is least efficient when it short cycles, due to the way they warm up. Also the more it turns on and off will cause more wear than if it ran continuous. This is all providing the old furnace ran normal cycles and not all the time when it was very cold.