Gas Fitting Fundamentals for the ARD Exam
Core concepts
The gas fitting portion tests your command of fuel gas codes, combustion theory, and safe installation practice. You must know the properties of natural gas and propane (relative density, heating value, ignition temperature), how manifold pressure and appliance input ratings relate, and how to size pipe so pressure drop stays within limits. Understand the difference between the gas control valve, regulator, and orifice, and how altitude or gas type changes orifice sizing. Venting categories (Category I through IV) and combustion air requirements for confined versus unconfined spaces are frequent topics, as are clearance-to-combustible rules and bonding/grounding of gas piping.
Traps candidates fall into
Questions often swap nominal pipe size with actual inside diameter, or ask for the demand load in cubic feet per hour when the input is given in BTUh. Remember the conversion: divide BTUh by the heating value (about 1,000 BTUh per cubic foot for natural gas, 2,500 for propane). Another trap is confusing a drip leg (sediment trap) requirement with a union location, or assuming a regulator is needed on every appliance when line pressure already meets the manifold rating. Watch for wording about "minimum" versus "maximum" clearance and about who may perform leak tests.
Worked example
An appliance rated 120,000 BTUh on natural gas needs a demand of 120,000 / 1,000 = 120 cubic feet per hour. Use that figure with the longest-run length and the appropriate pressure-drop table to select pipe size. Rule of thumb: always size to the longest equivalent length, not the straight-line distance, because fittings add equivalent length.