Fuel savings on a re-heat furnace.

John Martin

I am trying to justify the expense of repairing air headers on re-heat furnaces. Currently I have approx 175 square feet of missing insulation inside a 48" (od) pipe. After taking thermal imaging pictures the difference in temp of the non insulated pipe is 250 degrees. i.e 100 where the pipe is insulated and 350 where it is not. How do I calculate the MMBTU savings per year by insulating the pipe.