How To Install a Dishwasher in an Island

It is common today to install a dishwasher in an island located within the confines of a kitchen. Traditionally, dishwashers occupied a space in a set of cabinets that backed up against a wall, either exterior, or interior and adjacent to a kitchen sink. This allowed the builder or plumbing contractor to plumb the dishwasher drain into the kitchen sink waste and pick up the water supply for the dishwasher from a hot water stub-out in the kitchen sink cabinet. In an island configuration, the dishwasher must have its own waste and water supply unless it sits adjacent to a utility or vegetable sink. Planning is the key to installing a dishwasher in an island.

Preparation

There are a couple different ways to plumb in a dishwasher in an island

1. Refer to your building design.
2. Cut in a specific wye fitting into a building drain or kitchen sink drain line in the crawlspace or basement. This wye fitting will serve as a vent for the appliance.
3. Route the wye branch to the nearest wall and up through it into the attic space. Either connect the dishwasher vent to the nearest fixture vent, if size allows, or extend it alone through the roof.
4. Install a second wye branch fitting just ahead of the first one on the horizontal drain line. Make sure the branch lays flat with both fittings.
5. Extend the drain line up through the floor at the back of the dishwasher location or in an unused cabinet space adjacent to the dishwasher cabinet space.
6. At the proper height, install a 2” x 1 ½” x 1 ½” sanitary tee with the branch pointed toward the dishwasher.
7. Continue the drain line up to just below the countertop and plumb in the following fittings in their respective order: one 2” 45 elbow; one 2” 90 elbow; one 45 elbow. Take the drain line back down under the floor and connect it to the run of the last wye fitting.

Install the dishwasher

1. Remove the dishwasher racks, shipping blocks, and bottom front panel of the unit.
2. Install an air gap fitting in the countertop or the rim of an adjacent sink.
3. Plumb in a p-trap into the sanitary tee branch.
4. Adapt the top of the p-trap to the size of the dishwasher drain or install a Johnson tee on top of the trap.
5. Route the dishwasher drain hose to the large side (inlet) of the air gap. Route the small side (discharge) of the air gap to the trap. Connect with hose clamps. In the absence of an air gap, route the dishwasher drain hose as far up under the countertop as possible and fasten it in place, then back down to the trap.
6. Plumb in a hot water supply to the dishwasher location. Terminate the stub-out with a shut off valve or angle stop.
7. Connect a flexible water supply line from the angle stop to the inlet of the dishwasher.
8. Route a dedicated electrical circuit from the electrical panel to the dishwasher location.
9. Adjust the dishwasher legs for optimal height (in relation to the bottom of the countertop) and push the dishwasher into position.
10. Anchor the top mount flanges of the dishwasher to the bottom of the countertop with screws.
11. Make sure the dishwasher is level, plumb, and solid.
12. Turn on the water and check the unit for proper operation.
13. Reinstall the racks and the front lower panel.

Tips

Seal all holes in the floor with a good firestop sealant product.

Check your local building and codes department for appropriate regulations.

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