My question is Are HVAC systems and hot water heaters located in garaged required to be protected from impact by a bollard or wheel barrier?  IRC 2012 Section M1307.3.1 - Protection From Impact says yes.  What if the MEP appliances are located in a agrage but in a mechanical closet?  What if the closet has a large double door for access and maintenance?  Does the door provide a vehcle barrier? 

You are correct. According to section M1307.3.1 of the 2012 IRC, “appliances shall not be installed in a location subject to vehicle damage except where protected by approved barriers.” The local jurisdiction’s building official will need to define what is an approved barrier – whether it will be a bollard, wheel barrier, or other type of barrier. If the appliance is located in a closet in the garage, then it would not be subject to vehicle damage and therefore would not need any type of additional barrier.