Thermal efficiency of a space heater

means a measure of the percentage of heat from the combustion of gas or oil that is transferred to the space being heated, or in the case of a boiler, to the hot water or steam, as determined using the applicable test methods in Section 1604(e). Thermal efficiency of a commercial warm air furnace equals 100 percent minus percent flue loss, as determined using test procedures prescribed under 10 C.F.R. section 431.76.