You can easily calculate the output BTU by multiplying the input BTU by the efficiency percentage. For example a 100,000 BTU furnace at 80% efficiency will produce 80,000 BTU of heat while a 100,000 BTU furnace at 95% efficiency will produce 95,000 BTU of heat output.
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Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety. Ben Franklin
You left out a hole bunch of information needed to size an industrial furnace. Go back to the start and fill in the blanks. Then return and we might be able to point you in the right direction. Or call one of the many suppliers of industrial furnaces in the area, they would be glad to assist you.