This is a condensed field guide to the most commonly cited code violations and installation issues with residential mechanical systems. It is not a formal interpretation; the ones who decide what is "to code" are the authorities administering the building department in your area. Consult with them before beginning any construction project. This code check references the 2003 IRC, 2003 UMC, 2003 UPC, 2005 NEC, 2002 NFPA 54, 2004 NFPA 58, 2000 NFPA 31, and the 2000 NFPA 211.