How To Install A Replacement Dishwasher

by Michael Chotiner

When I started remodeling kitchens many years ago, one of the more uncertain parts of any project was installing the dishwasher. It's often a hassle to fit the machine and all of its associated hoses and wiring into the space left for it under the counter. But the hardest part of replacing a dishwasher can be getting the old dishwasher out.

The truth is that both phases can present challenges. Dishwasher manufacturers' spec sheets are supposed to give the exact width, depth and height, but I like to measure the actual machine itself and compare it to the available space under the counter before committing to installing it.

It's not only the overall width, depth and height that matter. You also need to consider the configuration of the existing plumbing and electrical system features that you'll hook up to. Look for protrusions from the floor and wall inside the dishwasher bay, such as pipes, conduits and junction boxes that may prevent you from sliding the new machine all the way back and flush with the counter edge. And if you go to the trouble of trying to slide the old machine out of its spot to make the recommended inspection, you just might find that a layer or two of flooring has been added since the dishwasher was installed. This can reduce the overall height from floor to the underside of the counter, trapping the old machine in place and restricting clearance for the new dishwasher.

If the old dishwasher is trapped, you've got a few options:

• Try raising the leveling legs to reduce the overall height so you can slide the machine out.
• Remove some of the flooring (neatly, so you can restore it) to gain the necessary clearance.
• In the worst case, cut away the leg bracket housings with a reciprocating saw.

Disconnecting the Old Dishwasher

Before trying to pull out the old dishwasher:

• Turn off the power to the circuit at the breaker.
• Shut off the water supply.

If you don't already know how to do these two things, call a professional installer to handle the removal of your old appliance.

The next step is to remove the front panel at the base of the old machine (above).

There you should find access to the dishwasher's own electrical box, the water supply and discharge hose connections (above).

At this point a pro would remove the cover from the electrical box and use a circuit tester or volt-ohm meter to verify that the power is off before disconnecting the wires and capping them with wire nuts.

If the dishwasher you're replacing is really old, your installer might not find all the connection points at the base front. For example, some old dishwashers had power cords and wall plugs rather than an electrical junction box. In such cases, your plumber may have to pull the old dishwasher out to disconnect the water, drain and power lines.

Next, an installer will find the water supply connection to the inlet valve and disconnect the water line, ready with a rag and container to catch any water that drips out, followed by the removal of the discharge hose connection (below).

Now that your professional has taken care of the plumbing and electrical connections, you can resume the manual removal. Don't forget to remove the screws that fasten the old machine in place. Open the door and look for them at the top of the dishwasher housing. Some machines also have fasteners along the sides of the door opening (below).

Slide the old dishwasher out of its bay and see what you have to work with.

Setting Up for the New Dishwasher

With the old dishwasher out of the bay, verify that the new machine will fit in the space. Slide it back far enough that the door (when closed) will be flush with the counter edge. If you determine that the available space is too short for the new machine, consider cutting off the leveling leg brackets and shimming the machine to a level position once it's in place. If the opening is too narrow, you may have to operate on the cabinets to widen it. Also, make sure that the extant water supply and electrical lines are sufficiently long to hook up to the new dishwasher when it's in place.

You can't put your new dishwasher just anywhere -- you need the right basic power and plumbing infrastructure where it will be placed:

• A copper-wire cable with ground wire connected to a dedicated 15- or 20 (recommended)-amp circuit. (Have a professional electrician install a dedicated circuit for your dishwasher if there's not one in place already).
• A 3/8-in. copper tube connection to a hot water line that delivers water at 120°F to the dishwasher at 20 to 125 psi (a professional handling the disconnect can check on this for you).
• A place to hook up the dishwasher drain line to the sink drain. If you're hooking up the dishwasher waste line to the sink drain line, there should be a waste tee with a branch for the dishwasher hose above the P-trap, just below the sink. Most disposals have a dishwasher drain inlet port, and if that's where you're going to make the hookup, be sure that the knockout on the port has been removed.
• Many local codes require dishwasher drain lines to be connected to an air gap (graphic below), which will prevent dirty water from a disposal or sink from backing up into the dishwasher, should the drain lines become clogged.

If you're not sure that all of the basic requirements are in place, consult with a licensed electrician and/or plumber before hooking up your new dishwasher. If you need to run new electrical cable and/or water supply tubing for the new dishwasher, it's a good idea to connect them to the house systems, route the lines as needed through the cabinets and pull them into the dishwasher opening with enough extra length to reach past the front of the cabinets.

Since most new dishwashers have all the necessary connection points at the front of the base and channels at the bottom of the frame to accommodate the lines, you'll do well to tape the lines to the floor in position so that you can slide the new dishwasher into place before making the connections. Remove the base panel below the door.

The Water Supply Connection

Because a simple mistake can result in a flooding disaster, you should hire a professional installer to hook up your water and drain, but it's smart to understand what they're doing. Here's the process they will follow:

• Wrap a 3/8 in. 90° NPT elbow with Teflon plumber's tape and thread it into the water inlet valve.
• One end of the water supply line should be connected to the hot water line at the shutoff valve. Connect the other end to the elbow with a compression fitting.

The Drain Connection

A new drain line is usually supplied with the dishwasher. Use it instead of reusing the old drain hose.

If an air gap is present, connect one end of the drain hose to one leg of the Y of the air gap with a clamp; the other end gets clamped onto the fitting at the discharge pump.

AIR GAP PICTURE

If an air gap isn't required, connect one end of the hose to the drainpipe and route it to the discharge pump through a hole bored high on the base cabinet side. This is called forming a "high loop," and it prevents dirty water from backing up into the dishwasher if the drain becomes clogged. Connect the other end of the hose to the discharge pump with a clamp.

The Electrical Connection

The power supply can be 2-wire with ground Romex or BX armored cable. Some dishwasher manufacturers offer a kit for installing a power cord with a wall plug. If you require direct wiring, hire a professional electrician.

Finishing Up

Once all of the connections have been made, set a level vertically against the closed dishwasher door. Adjust the leveling legs as needed to center the bubble. The dishwasher should be perfectly plumb (if not tilted ever so slightly backward) so it won't leak when the door seals begin to wear.

Fasten the dishwasher under the countertop using the brackets provided, making sure that whatever screws you use don't go through the top's wooden supports.

Turn the water supply and power to the dishwasher back on and run it through a cycle. Check all of the water supply and drain connections for leaks, and if all is well, re-attach the base panel.

Enjoy your new dishwasher.

About the author: Michael Chotiner writes about appliances and appliance care, including kitchen appliances such as dishwashers, for Home Depot. Michael's appliance installation tips for dishwashers are based on his years of experience in the home construction field, as well as being a homeowner. Home Depot's selection of dishwashers can be viewed on its website.