Three uniquely different water heaters and three uniquely different boilers were tested at nominal elevations of "sea level", 5,400' (1646 m) and 10,000' (3048 m) in accordance with the safety test protocols laid out in the appropriate ANSI Z21 standards for domestic tank type water heaters (Z21.10.1 and Z21.10.3) and boilers (Z21.13).

The objective of the test program was to either devise a method by which testing at "sea level" could predict the results at high altitude, and if that was not possible, identify test procedures that might be utilized to ascertain proper/safe performance at elevation. One subset of the program was to ascertain the appropriateness of the CAN1-2.17 test procedures for "predicting" and listing proper operation to 4,500' (1372 m). A second subset of the program was to determine if the reduction in input by natural derate or by the 4% derate rule would alter the classification of the venting Category of the product (Cat I, II, III or IV). A third subset of the program was to quickly review the possibility that vent piping (intake and exhaust) simulators could be used to eliminate the tedious task of setting up hundreds of feet of vent and air intake pipe in order to run testing at elevation on horizontally vented, fan assisted combustion products. This report should be beneficial to gas appliance and control manufacturers, gas utilities, appliance testing/listing agencies and code officials responsible for the proper operation and installation of gas appliances in high elevation areas of North America.

An attempt has been made in the writing of this paper to accommodate all levels of gas appliance expertise, from the experienced gas appliance engineer to persons new to the gas appliance business and with or without benefit of an engineering background.