Air Conditioning, Heating & Refrigeration News, Feb. 10, 2014, by Dan Vastyan.
http://www.achrnews.com/articles/125759-rtus-cool-more-space-using-less-energy

"Some industry experts in the HVAC industry consider gas-fired condensing combustion heating systems to be the final frontier in rooftop heating technology.  As seen during the formative years, throughout the development of high-efficiency residential furnaces, several manufacturers boast condensing rooftop equipment on the market. Most product lines available today are in the 90-92 percent efficiency range, but a few approach 95 percent."