Goodman Natural Gas to LP Converstion Kit for Single Stage Furnaces. Goodman has become one of the largest manufacturers of residential and light commercial air conditioning, heating, and indoor air quality products and systems by focusing on just one thing - building the most reliable and refreshingly affordable indoor comfort products in the market. The complete line of Goodman brand products are built on the principles of founder Harold Goodman, a former air conditioning contractor. Building Goodman products to Harold's standards, and protecting those products with some of the best limited warranties in the industry, has helped to make the Goodman brand widely recognized as a leading brand in the residential and light commercial heating, ventilation and air conditioning industry today.