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How to Install a Dishwasher
Harry Sawyers, This Old House magazine 30-Dec-2008 10:28:33 AM
1 to 2 hours
dollar sign
$450 to $2,000
Skill Level: Moderate
involves basic plumbing and electrical work

Boy, the retired couple you bought your house from left behind one incredibly energy-efficient dishwasher! Okay, maybe just efficient to them, because they didn't need to run it more than once a week and only had a full load when the grandkids came for Thanksgiving. But you—you pack that thing with pots, plates, and glasses every night, sometimes again in the morning. Its age is starting to show, especially in your electric and water bills.

Time to switch it out for a new Energy Star–qualified dishwasher, which can save you more than $30 a year on power and almost 500 gallons of water. These units have sensors that self-adjust to wash with just the right amount of water. And today's models are so good at scrubbing, you don't have to prerinse in the sink—which translates to even less of your hard-earned money and time down the drain. But the biggest cost-saver of all is that you can install one yourself in an afternoon, as This Old House technical editor Mark Powers demonstrates on the following pages. No plumber, no electrician—and no worries that you're squandering your retirement money on a load of clean dishes.

Tools for This Project

flathead screwdriver



fitted with 1 1/4-inch and 2-inch hole saws

spade bit

1-inch spade bit

needlenose pliers


adjustable wrench

Adjustable wrench

Tube Bending Springs

Tube Bending Springs

close quarter tubing cutter

Close-quarter tubing cutter

torpedo level

Torpedo level

wire strippers

Wire Strippers

Supplies You Will Need

The majority of built-in dishwashers come in only two sizes: 24 inches wide and 18 inches wide, both sized to fit under a standard 25-inch-deep and 36-inch-high counter. (Be sure to get a built-in dishwasher, not a portable one, which uses temporary connections at a sink tap and outlet.) Look for the Energy Star label on any model you buy—the criteria for dishwashers became more stringent in January 2007.

to make the turn from the dishwasher's inlet to the copper supply line. This is a standard part for dishwashers and may be included in a dishwasher installation kit.


to bring water to the dishwasher. (The measurement refers to the pipe's outside diameter.) A 10-foot coil should be plenty.

The number also refers to outside diameter. Each includes a brass ferrule (or compression sleeve) and a compression nut.

6. ELECTRICAL WIRE NUTS to connect wire ends.
Get ones that will fit two 12-gauge wires—either yellow or red.

to secure the electrical cable to the junction box on the dishwasher.

to attach the dishwasher's 5⁄8-inch drain hose to the sink's drain tailpiece.

to hang the drain hose on the cabinet wall.
diagram explaining dishwasher installation


Energy-efficient and water-saving dishwashers may have the most up-to-date technology, but thankfully they have the same three basic connections dishwashers have been using for decades: a water supply, a drain line, and an electrical hookup. That means if you're replacing a dishwasher, you only need to break these connections from the old appliance and reattach them to the new one. (Shut off power at the breaker panel and close the hot-water valve under the sink first, and be sure to unscrew the old unit from the underside of the counter before pulling it out.)

The existing electrical wiring is still good, but both plumbing lines should be replaced. Dishwashers come with drain hoses, but you'll need to buy a supply pipe—preferably copper tubing, which TOH plumbing and heating expert Richard Trethewey uses instead of braided steel. "Copper is time-proven," says Richard. "Inside a braided line is rubber, which can eventually fail. Copper lasts 60 to 80 years—longer than any dishwasher."

Though traditionally dishwashers get hooked up to the hot-water supply, you can save even more energy by connecting to the cold water because the heating element in the dishwasher uses less power than a water heater. However, check manufacturers' literature—some companies' models must be supplied with hot water.

The most difficult part of the installation may be snaking the copper tubing through the cabinet without kinking it. An invaluable tool for this is a tube-bending spring, which fits either inside the pipe or around it and bends it with even pressure. But Richard points out that it's the easiest of the connections—the drain line—that actually causes the most trouble. It must be installed strapped up high in an upside-down U to prevent sink backflow from going into the dishwasher. Also, if you're installing a model that sits flush with the front of the cabinets, you may have to drill new, lower holes from the dishwasher bay to the supply valve so the plumbing lines snake along a narrow inset at the back of the unit, allowing you to push it all the way to the wall.

Luckily, the electrical connection is fairly straightforward; just make sure to clamp the wires—be they metal-sheathed BX cable or vinyl-wrapped Romex—to the unit's junction box. This protects against electrocution should there be any leaks.

man inserting tube spring in water supply

Step by Step

1. Set up the water supply

For flush-front (fully integrated) dishwashers: Using a drill/driver fitted with a 2-inch hole saw, make a hole through the side of the sink cabinet facing the dishwasher bay, 3 inches up from the floor and 2 inches in from the back wall. If this hole falls below the cabinet floor, make two 11⁄4-inch holes at the back of the cabinet floor. (For semi-integrated models, reuse the existing holes.)

Carefully uncoil the copper tubing and loosely thread it from the dishwasher bay through the cabinet side and up into the cabinet via one of the floor holes. Uncoil enough copper to get past the front of the bay. Using a tubing cutter, cut the line. Insert a narrow tube-bending spring inside the end of the copper nearest the hot-water valve. Use the spring to shape the tubing toward the valve then down to the hole in the cabinet. Be careful not to kink it.

Slide a compression nut, then a ferrule over the end of the tubing at the valve. Hand-tighten the nut over the ferrule and onto the valve. Using an adjustable wrench, tighten it another quarter turn.

Tip: Tube-bending springs can fit either inside or outside a pipe. The inside springs can only be used on a pipe's ends, but they make tighter turns. Use outside springs to gently curve the middle of a pipe.

man positioning the water and electrical lines

2. Position the water and electrical lines

Find the two front-to-back clear paths on the underside of the dishwasher—these are meant to keep the copper tubing and electrical wiring away from the motor as they run from the back of the dishwasher bay to the front of the appliance. Measure the distance from these paths to the sides of the dishwasher. Transfer the measurements to the floor inside the bay. Note which side leads to the water hookup and which side is for the wiring.

Using an outside bending spring, shape the copper pipe so it wraps down the cabinet side and along the mark for the water-pipe channel. Twist the electrical wire so that it lies in the correct path as well. Use tape to secure both to the floor in position over their marked lines.

man hooking up the water supply

3. Hook up the water supply

Lay down a tarp to protect the floor and tip the dishwasher on its back. Remove the cover panel at the bottom of the unit. Wrap Teflon around the water inlet's threads. Screw a brass elbow onto the inlet. Tighten it with an adjustable wrench.

Stand the dishwasher up and push it up to the bay. Check that the water and electrical lines are properly aligned. Feed the end of the drain line from the dishwasher through the side of the cabinet and up via the unused floor hole. Then have a helper guide the drain line as you slowly slide the dishwasher in place

man sliding the nut and tightening it to the inlet

4. Tighten the nut onto the inlet

Using the inside bending spring, turn the copper supply to the elbow. Cut off any excess pipe but leave 2 inches of straight copper for the compression fitting. Slide a compression nut and ferrule over the end of the pipe and hand-tighten the nut onto the inlet. Using an adjustable wrench, tighten it another quarter turn.

Tip: Never hold a dishwasher by its door as you move or tilt it.

electrical wires being connected

5. Make the electrical connection

Slide a cable clamp over the end of the exposed wires until it's around the plastic or metal sheathing bundling the wires together. Using a screwdriver, tighten down the clamping bracket over the sheathing to hold the wires in place.

Unscrew the star-shaped nut on the clamp, then push the wires and threaded end of the clamp through the hole in the side of the unit's junction box. Hand-tighten the nut back on the clamp from the inside of the box. Tighten the nut with pliers or a screwdriver.

Line up like colors of wire together—white to white and black to black—and tighten them together with wire nuts. If you have Romex (plastic-sheathed) cable, connect the green ground wire to the dishwasher's green or bare-copper wire with a wire nut.

If you're using BX cable, the armored jacket works as a ground when it's clamped to the junction box. Wrap the exposed tip of the dishwasher's ground wire around a mounting screw on the junction box and clamp it down with the screw.

Stuff the wires into the box and cover it with the metal cover plate. Screw the plate to the box.

a hose clamp over the drain line

6. Attach the drain line

Slip a hose clamp over the end of the dishwasher's drain line, and push the hose over the sink drain inlet—either branching off the drain tailpiece or the side of the garbage disposer. Take care not to kink the line or wrap it around the spray hose line. Slide the hose clamp over the connection and turn the screw to tighten it down.

man inserting tube spring in water supply

7. Attach the strapping to cabinet wall

Wrap a loop of plumber's strapping around the drain line with enough excess to match up a pair of holes. Hold the hose and strapping against the back of the cabinet so it makes an arc that's higher than the drain inlet. Using a screwdriver, attach the strapping to the cabinet wall.

man fixing the dishwasher under the cabinet

8. Screw the dishwasher in place

Reach down and adjust the feet on the front of the dishwasher until the mounting brackets touch the underside of the counter.

Open the dishwasher door. Holding a torpedo level against the inside top of the dishwasher, adjust the feet until it's level side to side.

Screws are drawn in the mounting brackets to fasten dshwasher underside of the countertop

9. Fasten dishwasher underside of the countertop

With the dishwasher level, fasten it to the underside of the countertop by driving screws through the mounting brackets. Replace the cover panel at the base of the unit.

Turn on the power and water supply. Check for leaks at the water connections over the next few hours. If any appear, turn off the water and tighten the compression fittings slightly. If no leaks appear, test-run the dishwasher.

newly installed dishwasher

10. Check for leaks

Turn on the power and water supply. Check for leaks at the water connections over the next few hours. If any appear, turn off the water and tighten the compression fittings slightly. If no leaks appear, test-run the dishwasher.

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