FIX, AAON, Inc. AAON as well as Tecogen Inc. TGEN. AAON, Inc.: Based in Tulsa, OK, AAON engineers, manufactures, and markets air conditioning as well as heating equipment. Overall, higher revenues, improved productivity, lower SG&A expenses (as a percentage of sales) along with a lower tax rate bode well for AAON despite inflationary cost pressures.