Your furnace breaks down in the middle of the winter, and you have already done every check that you know of in an effort to get the unit back up and running. Once you have given up, you give in and decide to call an HVAC contractor to lend you a hand. Flipping through the phone book, you see many large ads that make various promises, but how are you going to pick one? No one has the time or money to spend on a technician who doesn’t know what they are doing. So, you should look for a company that promotes NATE certified technicians.