Gas-fired definition
Gas-fired means the combustion of natural gas, or a coal-derived gaseous fuel with a sulfur con- tent no greater than natural gas, for at least 90 percent of the average annual heat input during the pre- vious three calendar years and for at least 85 percent of the annual heat input in each of those calendar years; and any fuel other than coal or any other coal-derived fuel for the remaining heat input, if any.