Fixtures, Faucets, and Appliances
What this domain tests
This domain tests installation and connection details for water closets, lavatories, sinks, showers, dishwashers, washing machines, and water heaters. Expect questions on flow rates, trap sizes, rough-in dimensions, accessible installation, and safe appliance connections.
Core fixture rules
- Water closets typically have a 12-in. rough-in, with 10-in. and 14-in. versions available. The closet flange must be secure and the wax ring properly seated. Federal maximum flush volume is 1.6 gpf, though many jurisdictions require 1.28 gpf or less.
- Lavatory and kitchen faucets are commonly limited to 2.2 gpm, and showerheads to 2.5 gpm; local rules may be lower. Check the aerator and supply stops when flow is poor.
- Trap sizes: 1¼ in. for lavatories, 1½ in. for kitchen sinks, and an integral trap for water closets. A fixture trap seal is normally 2–4 in. deep.
- Accessible design: lavatory rim no higher than 34 in., knee clearance about 27 in. high, and water-closet seat height about 17–19 in.
- Dishwashers need an air gap or high loop to prevent backflow. Washing-machine standpipes are commonly 18–30 in. above the trap.
- Water heaters need a temperature-and-pressure relief valve, a discharge pipe to a safe location, and an expansion tank on a closed system.
Worked example
You are replacing a lavatory faucet. Confirm the supply stops shut off, install the new faucet with a new supply connection, and connect the 1¼-in. trap. Check the flow rate and aerator, then run hot and cold water and inspect under the cabinet for leaks. Do not seal the cabinet until the trap and stops are dry.
Traps that cost marks
Installing an undersized trap, omitting the dishwasher air gap, using flexible connectors inside a wall, and forgetting the water-heater drain pan or expansion tank.
Key points
- Match trap size to the fixture: 1¼ in. lavatory, 1½ in. kitchen sink.
- Know common flow limits: 2.2 gpm faucets, 2.5 gpm showerheads.
- Accessible lavatory rim: 34 in. maximum; seat height 17–19 in.
- Dishwashers need an air gap or high loop.
- Water heaters need T&P relief, safe discharge, and expansion control.