Yes, get the temperature of the furnace exterior surface to 350F for 30 minutes and the XTC will be fully cured. Let the temperature come up to 350F slowly and hen back to room temperature slowly.
For an exterior application, please remember to apply 1-2 thin, covering coats of XTC Primer before the XTC. The XTC Primer provides the rust protection.
Please be sure to check out the XTC Primer Complete Directions and the XTC Complete Directions before you begin your project.