ASTM D2157-94(2013)

5.1 This test method relates efficiency of operation of domestic heating equipment to clean burning. Reducing combustion air in a burner gives more efficient operation. The extent to which combustion air can be reduced is limited by the onset of unacceptable smoke production. By delineating the relation between smoke density and air supply, this test method (together with net stack temperature data) defines the maximum efficiency for a given installation at any acceptable smoke level.

5.2 For certain types of equipment, such as the rotary wall-flame burner, too much excess air will cause smoke as well as too little. For these cases, the point of minimum excess air at the acceptable smoke level indicates the optimum efficiency.

5.3 The operating temperatures of the equipment will affect these test results. The relation of excess air to smoke density is thus susceptible to some change at different points in an operating cycle. In practice, an adequate compromise is possible by operating the burner for 15 min before any readings are recorded and then obtaining the test data within a succeeding 25-min period.

5.4 Under laboratory conditions, CO_{1.1 This test method covers the evaluation of the performance of distillate fuels from the standpoint of clean, efficient burning. It is intended primarily for use with home heating equipment burning No. 1 or No. 2 fuel oils. It can be used either in the laboratory or in the field to compare fuels using a given heating unit or to compare the performance of heating units using a given fuel.}