Codes, Standards, Permits, and Jobsite Safety
The most restrictive requirement governs
Codes set minimums; manufacturer listings and instructions set specifics. When they conflict, follow the more restrictive requirement, and never install equipment in a way that violates its listing. Know which documents govern your work: the mechanical code and residential mechanical provisions for installation and ventilation, the fuel gas code for gas piping and combustion air, the electrical code for wiring methods and disconnects, the energy code for insulation, sealing, and controls, and referenced standards for ventilation rates, refrigerant safety, and duct construction.
Permits and inspections are part of the job. Pull the permit before work, schedule rough-in and final inspections, and expect the inspector to check clearances, venting, combustion air, condensate, electrical disconnects, and labeling. Refrigerant handling is regulated: technician certification, recovery, and - for A2L refrigerants - charge limits, leak detection, and ventilation per the safety standard.
Safety is not separate from the trade. Lockout/tagout before servicing, verified with a meter. Fall protection where required (commonly 6 ft in construction, 4 ft in general industry). Ladder and roof access rules, confined space entry procedures, and proper PPE for brazing, refrigerant (frostbite and asphyxiation risk), and electrical work. Test for CO and confirm combustion appliance zone pressure before leaving a tightened house.
Traps: installing to a code minimum when the listing demands more; skipping the permit; assuming an existing vent is adequate for a new appliance; treating A2L refrigerants like legacy A1 refrigerants.
Rule of thumb: if the instructions and the code disagree, satisfy both by meeting the stricter one, and document the decision.