Direct line from water tank to dishwasher?

graywings123February 16, 2012

I live in a 91 year old house that has seen a lot of renovations. The natural gas water tank is located in a utility closet in the kitchen. There is a crawl space below.

Next to the closet is a space where I would like to install a dishwasher. Is this possible? I have never seen dishwashers installed anywhere except next to a sink.

Could a plumber run a short line from the water tank to the dishwasher and then tap into a waste water line that is somewhere under the kitchen floor?

I realize the short answer is "call a plumber," but I want to get a feel for whether this is theoretically feasible.

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Sophie Wheeler

Logistically, in addition to the new electrical circuit that the DW will need, as a health and safety measure a DW will need to have an "indirect drain" such as into the sink's trap or laundry stand pipe. It cannot drain directly into the home's drain system. That's one of the reasons that a DW is located next to the sink.

The main reason that a DW is located next to the sink is that it is incredibly awkward and messy and drippy to have it located anywhere else. You take your wet dishes that you just scraped and ran under the tap and they take a drip trip around the kitchen to go to the DW rather than just to the DW right next to the sink. Functionally, it's easier to just handwash if the DW has to be located more than about 18" from the sink.

    Bookmark   February 16, 2012 at 11:31AM
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"It cannot drain directly into the home's drain system. "

That depends on what code and any local changes to the model codes.

Air gaps are sometimes required in drain lines, but high loops are allowed in many places.

The drain can then go into a garbage disposal or a T on the sink drain before the trap.

You need to know what your AHJ expects and requires.

Ask what the base plumbing code is in your area, and how to obtain a copy of local changes.

    Bookmark   February 16, 2012 at 11:44AM
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AHJ - what does that stand for? Agency having jurisdiction?

The electrical is already there because there is an old (1970's maybe) working wall oven there that would come out.

Hollysprings, the dishwasher is next to the sink now and is terribly inconvenient. It is turned 180 degress on a very short peninsula. I have to walk around the peninsula - walking out of the main kitchen area - to access the dishwasher.

Moving the dishwasher next to the water tank would move it into the kitchen and decrease the walking distance to load and unload. It would still be near the sink, though I don't pre-rinse my dishes.

But, waste water aside, can anyone answer whether it is possible for the dishwasher to have its own tap coming off the water tank?

    Bookmark   February 16, 2012 at 1:57PM
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Sophie Wheeler

The supply isn't the problem. You can T off of any hot water line, add a shut off and you've got the hot water you'd need. However, the drain will be a problem--potentially unsurmountably so. And a 220 line will not provide the 110 voltage that a DW uses. That will have to be replaced as well.

Do you have a diagram of your current situation? If I'm picturing it correctly the DW is on the peninsula facing the breakfast area? If that's the case, it should be a relatively simple matter of tweaking to just turn it around to face your sink.

    Bookmark   February 16, 2012 at 4:26PM
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She can probably use the cables that were used for the oven.

    Bookmark   February 16, 2012 at 8:13PM
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AHJ = Authority Having Jurisdiction. There's some finer points in the industrial/commercial world but for most homeowners it means the local building code enforcement folks.

It's relatively easy to convert a 220v circuit to a 120v circuit, although you should consult with licensed electrician. You can't, for example, just swap receptacles.

    Bookmark   February 17, 2012 at 12:37AM
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Hollysprings, I wish it were as easy as turning the dishwasher around, but it backs into another cabinet run at an L intersection with the peninsula.

It is a small kitchen, and any other options for having the dishwasher in the kitchen involve moving the sink.

There is an existing 110 plug in the area where I a trying to place the dishwasher.

Isn't a sink trap just a squiggle of pipe? Couldn't a plumber install a dedicated trap for the dishwasher and then tap into the waste water line? Or is that easier said than done?

    Bookmark   February 17, 2012 at 10:52AM
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Traps require vents.

You may be able to extend the drain line using smooth walled tubing to a sink if the distance is not to far.

    Bookmark   February 17, 2012 at 2:32PM
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If you'd post a diagram of your kitchen area, showing your cabinetry layout as well as the location of your current and proposed DW, you could receive more useful suggestions. Show any vent locations as well.

    Bookmark   February 17, 2012 at 3:20PM
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Everybody seems to be trying to make a simple job complicated....

If I am understanding her information correctly she is only anticipating moving an existing dishwasher about 5 to 8ft.

She oviously already has a 120v power source so it would be no real problem for an electrician to tie in at the current location then drop and romax down into the crawl space and pop it up to an new outlet at the new location.

She most assuredly may have a tee put on the water heater line as she suggests, then have an angle stop attached on that line to transition from pipe to the 3/8 tubing for the dishwasher. The only caveate here is that in some jurisdictions they would require attaching a tag to that valve clearly marking it as the dishwasher supply cutoff valve.

Now for the drain....

ALL CODES require a high loop.

Under the UPC and in some jurisdictions under the IRC you are also required to have an air gap.

The simple solution would be to lengthen the existing line from the DW and connect it to the drain where it is currently connected. If that is not practical they can then install a standpipe, which not only passes as an indirect waste, it is also an air gap.

If this location is under the UPC the standpipe could pass through the floor to a trap below, and if the fixture arm from that trap to a vented branch is equal to or less than the maximum allowable length for a fixture arm, no additional vent is required.

If she is under the UPC the trap must be on the same floor as the DW and she would need a vent on the riser, however if she has no other AAV's in the house, they could attach an AAV on the top of that riser.

    Bookmark   February 17, 2012 at 6:40PM
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Thank you all so much. I will have to digest all this advice and get a better understanding on the plumbing lines and where the air vent is. I'll come back with more questions later.

I'll work on photos and sketches.

    Bookmark   February 18, 2012 at 8:48AM
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"ALL CODES require a high loop. "

Some locations sill require air gaps.

A simple high loop may not be allowed.

    Bookmark   February 18, 2012 at 3:12PM
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