How can I calculate energy loss from a leak in a large furnace??? I currently am working on a large furnace about 1200 square feet. To heat the furnace we use a combination of air and methane at a ratio of 9.54:1. There is currently a hole in the furnace and I would like a formula to calculate the energy loss. We have the temperatures and the pressures to use in the formula. If you can please give me some tips of an equation to determine the energy loss I would greatly appreciate it. Thank you.