This standard includes a. a test method for cyclic and part-load performance@ b. methods for interpolating and extrapolating test data@ and c. calculation procedures for establishing seasonal performance. This standard applies to central furnaces with inputs less than 225@000 Btu/h (65.92 kW) and boilers with inputs less than 300@000 Btu/h (87.90 kW)@ having gas@ oil@ or electric input@ and intended for use in residential applications. This standard also applies to furnaces with inputs less than 225@000 Btu/h (65.92 kW) contained within the same cabinet with central air conditioners that have rated cooling capacities of 65@000 Btu/h (19.04 kW) or less. This standard applies to equipment that utilizes single-phase electric current or lowvoltage DC current. The procedures are intended to be used to compare energy consumption measures of various furnace and boiler models. They are not intended to provide an absolute measure of performance in any specific installation configuration@ as the effects of heating system installation variables are not fully taken into account. PURPOSE The purpose of this standard is to provide procedures for determining the annual fuel utilization efficiency of residential central furnaces and boilers.