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Maintaining A Healthy Pulse by William A. Lotz, P.E. The pulse furnace was developed by the Institute of Gas Technology in Chicago back in the 70s. It has been the greatest advance for residential gas furnaces since the invention of the return fan. Lennox was the first to market the product for warm-air furnaces and Hydrotherm sells a pulse hot-water boiler. Several companies have jumped on the bandwagon with condensing furnaces. Unfortunately some of these companies have had terrible corrosion problems with their product. The pulse furnace is only made by Lennox. It is a condensing furnace, meaning that water condenses in the process of extracting Btus from the exhaust gas. This results in a thermal efficiency of over 90 percent. Many other companies