Piping, Fittings, and Fuel Gas Systems
Clean, dry, and correctly sized
Refrigerant piping must be sized for pressure drop and oil return. Use ACR copper, braze with a nitrogen purge to prevent internal oxidation, and protect adjacent surfaces. Suction risers may require a double riser or an oil trap to keep velocity adequate at part load. Pressure-test with dry nitrogen - never oxygen, never refrigerant from a cylinder used to pressurize - and evacuate to a deep vacuum with a decay test before charging.
Hydronic piping adds its own rules: circulators sized to head and flow, air separation at the hottest, lowest-pressure point, expansion tanks sized for system volume and temperature swing, relief valves piped to a safe discharge, and backflow protection on makeup water. Glycol requires derating of capacity and pump curves.
Fuel gas work follows the fuel gas code. Size pipe by the longest-length method with an allowable pressure drop, count the equivalent length of fittings, install a sediment trap and a listed shutoff valve at the appliance, support the piping, and bond CSST per the manufacturer's instructions. Orifices and regulator springs must be changed for a fuel conversion, and combustion air must be provided to the appliance space.
Traps: skipping the nitrogen purge; using a soap test only at the manifold; forgetting that a new appliance with higher input may require larger pipe; omitting combustion air in a tightened building.
Worked example (combustion air): the classic rule allows 50 ft³ of volume per 1,000 Btu/h of input for conventional infiltration. A 100,000 Btu/h appliance needs about 5,000 ft³, roughly a 25 × 20 × 10 ft space.