Dishwasher directly to drain stack

greenkiwiSeptember 6, 2012

We are remodeling our kitchen and were wondering whether or not it was possible to have the dishwasher drain directly into the drain stack, with a drain entrance above the sink drain, vented up to the roof?

The reason I'm asking is we need to have an effective "air gap" and while I believe that I should have an air gap, I'd rather not have that come through my counter.

We are reworking our current drain stack anyway and I figured that if I could have the DW drain out directly to a vented stack, above the sink drain, that it might obviate the need for an air gap.

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If you forgo the air gap, the solution is to give the drain hose a "high loop" under the counter and connect the normal way.

    Bookmark   September 6, 2012 at 8:21AM
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Quote: "If you forgo the air gap, the solution is to give the drain hose a "high loop" under the counter and connect the normal way."


All dishwashers are required to have a high loop & terminate into an approved indirect waste receptor.

If you are under the UPC you are required to have an air gap at the top of the high loop. The IRC does not require the air gap, but many local codes under the IRC require the air gap.

The line from the air gap or the top of the high loop is then required to fall below the trap and rise up again to the point of final connection, whether that is to a disposal inlet or a vertical extension tailpiece with a dishwasher inlet port.

If the dishwashers is adjacent to an outside wall they make an airgap that is installed in the wall and it has a drip port through the wall so any excess water will drip outside the structure. The built in airgaps must have a removable service access panel on the inside wall to permit servicing the air gap.

Another option, if approved by your local AHJ is to install an 18" standpipe under the cabinets and discharge the line from the high loop would drop below the trap than back up and discharge into the standpipe in the same manner as a washing machine drain line.

    Bookmark   September 6, 2012 at 10:03AM
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Was I really that wrong? Aside from the code references I thought I was saying a similar thing. High loop under cabinet + connect normally (eg. to garbage disposer port or dishwasher port on tailpiece).

As for the code, what happens when code requires the air gap, but folks don't want it? Right or wrong, they seem to get the high loop.

    Bookmark   September 6, 2012 at 10:40AM
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As a side note, isn't a high loop incorporated into most, if not all dishwashers? Looking at the hose on the side of the unit, that seems to be what they're doing. Just wondering.

    Bookmark   September 6, 2012 at 10:45AM
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I believe he was saying that even with a 'high-loop' an air gap is required by the UPC.

    Bookmark   September 6, 2012 at 5:15PM
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For what it's worth, here's an inspectors' discussion on the topic:

Here is a link that might be useful: Inspection News

    Bookmark   September 6, 2012 at 5:28PM
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Regardless of what features may be built into the dishwasher, the codes require that ALL residential dishwashers MUST HAVE a high loop on the drain line.

Where required, an air gap is at the apex of a high loop in the drain line.

The line is then requiired to drop down below the level of the trap and rise up to the final connection point above the trap, either on a disposal inlet port or a dishwasher inlet port on a vertical tailpiece.

There is one variation to the high loop that is commonly done on commercial dishwashers although I have only seen it done twice in residential service.

If the dishwasher is installed on a concrete floor that is covered with ceramic tile they can install a 10"x10" sump that is 4" deep, with a floor drain in the bottom of the sump. The dishwasher drain line can then discharge into the sump providing the lowest point of the discharge line remains a minimum of 2" above the flood level rim of the sump.

    Bookmark   September 6, 2012 at 10:07PM
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