How to Install a Dishwasher
By: Jared Libby
Whether you’re putting in all new appliances or simply replacing a worn-out machine, installing a dishwasher yourself is a DIY project that’s not that difficult and can save you a hefty installation fee.
Preparations for Dishwasher Installation
The first step is making sure the machine will fit in the opening. Most standard dishwashers require a 24” opening. If you’re installing new cabinets, it’s important to consider the width of the dishwasher ahead of time. The height of most machines is adjustable within certain limits, but check to be sure the dishwasher you plan on purchasing will fit your opening before buying.
Depending on your cabinet configuration, you may need to drill one or more holes to run supply lines, electrical wiring, and the drainpipe through. Hole saws make quick work of drilling larger diameter holes.
Remove the faceplate at the base of the machine to access the supply line inlet and electrical box. It’s a good idea to connect the wiring, drain, and supply lines before pushing the dishwasher into the cabinet, since it makes it easier to access the underside of the machine.
Connecting the Drainpipe
Start by connecting the drainpipe to the discharge pump. Many local building codes require dishwashers to be vented using an air gap to prevent the siphoning of water from the sink drain or disposal. Mount the air gap in one of the sink holes or drill a hole for it in the countertop. Connect the drainpipes to the air gap and secure them with hose or spring clamps.
If an air gap is not required, loop the drain hose up near the top of the base cabinet, and attach it to the wall with a strap to prevent backflow from the sink.
Run the drainpipe to the inlet of the garbage disposal and secure it with a clamp. Many garbage disposals have a plug in the inlet, so be sure to remove it first.
If there isn’t a garbage disposal or an existing drain for the dishwasher, replace the drainpipe under the sink with a dishwasher branch tailpiece and install it above the trap under the sink.
Connecting the Supply Lines
Most dishwasher supply lines are 3/8” diameter, but check to make sure you’ve got the right parts before starting the job. Begin by turning off the water and installing a dual outlet shut-off valve to connect the dishwasher supply line to the hot water pipe under the sink. One outlet on the valve provides hot water for the sink faucet while the other attaches to the dishwasher supply line. This will allow you to turn the water off to the dishwasher separately from the faucet.
Connect one end of the supply line to the shut-off valve and the other end to the water inlet on the underside of the dishwasher using a right angle elbow.
Where needed, apply Teflon tape to the male threads to prevent leaks. Supply lines should be hand tightened then given a solid quarter turn with a wrench.
Connecting the Electrical Supply
Always be sure to cut off the power to the dishwasher by flipping the circuit breaker before attempting to connect the electrical supply. Run the cable through the back of the electrical box on the dishwasher, and connect the hot (usually black) and neutral (white) wires to the corresponding wires in the box using wire nuts. Be sure to connect the ground wire to the green screw and replace the cover on the box.
Turn the water back on and check for leaks, then turn on the power and run the dishwasher through a full cycle. If everything works properly, slide the machine into the cabinet, being careful not to crimp or pinch the pipes. Plumb and level it by raising and lowering the adjustable feet on either side.
Screw the dishwasher to the underside of the countertop to hold it in place. When attaching the mounting screws to the plywood used to support a stone countertop, be sure the screws do not protrude into the stone.
Attach the faceplate to the base, and your new dishwasher is ready to go!
- Examine the dishwasher before bringing it home. Look for scratches or dents and make sure the necessary hardware is included.
- Check the size of all supply lines and connecters before installing a new machine.
- Make sure to close all shut-off valves and turn off the circuit breaker before disconnecting an old dishwasher.
- When disconnecting an existing machine, be prepared with towels and a shallow pan to drain any excess water remaining in the lines.