Fixtures, Appliances, and Water Heaters
Heaters: pressure, temperature, and relief
Water heater questions are really about expansion and relief. A closed system with a backflow preventer or check valve creates a thermal expansion problem, so add a listed expansion tank on the cold inlet side. The temperature and pressure relief valve must be listed, matched to the tank rating, and piped full size with a discharge that terminates by gravity within 6 in. of the floor (or outdoors) - no threads, no cap, no valve, and material rated for hot water such as copper or CPVC, never PVC.
Gas appliances need a sediment trap (drip leg) ahead of the controls, a listed connector, and combustion air per code.
On the fixture side, know clearances and traps. A water closet needs about 15 in. from centerline to side wall and 30 in. of clear width, with a 12 in. standard rough-in from finished wall to closet bolts. Each fixture gets its own trap, one trap per trap arm, and a dishwasher needs an air gap or a listed high-loop.
Traps: capping, reducing, or threading a T&P discharge; running it into a floor-drain trap; double-trapping or sharing one trap between two fixtures; and assuming an expansion tank is needed on an open system with no backflow device.
Rule of thumb: a 150 psi relief setting is not a working pressure. Normal operation should stay well below the rating - near 80 psi downstream of a pressure-reducing valve.