In cooperation with GRI (Gas Research Institute) and AGAL-R&D (American Gas Association Laboratories), ten pulse-combustion, condensing warm air furnaces were designed, built, and field tested during the 1979-80 heating season. The purpose of the test was to evaluate the real-time operation of a pulse furnace in regard to efficiency, sound and comfort levels, operational reliability, and durability. The test results, in addition to a great deal of laboratory-generated data, were the basis for the decision to commercialize the pulse-combustion concept into a line of gas-fired furnaces.