Fiat Inc. has acquired Burt-Burnett Inc., a 25-year-old commercial heating and air conditioning company based in Tempe. John Hooper, founder of Mesa-based Fiat, said Burt-Burnett was struggling financially. “We saved 20-some people’s jobs,” Hooper said. “They weren’t in the strongest position and so we stepped in and helped them gain a foothold.” He said Fiat paid $400,000 to buy the controlling stake of Burt-Burnett. Fiat will serve as the holding company and will market the company…