As with any highly skilled trade, heating, ventilation and air-conditioning (HVAC) contractors and technicians have their own industry language. They use a variety of concepts and terms that most of us do not deal with on a day-to-day basis. A good HVAC contractor will take the time to explain everything to you when installing a new system or performing maintenance, but it doesn't hurt to have some basic knowledge so that you can ask intelligent questions and ensure the efficiency of your equipment. Here's a list of some of the terms you may confront.