Are air gaps necessary on a dishwasher? How do you avoid it?

brianadarnellApril 18, 2011

My dishwasher's installation guide references the possibility of an air gap. How do you know if you will need one or not?

I dread the thought of an air gap that would change the look of my siligranit super single.

How do you avoid needing an air gap?

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Secure a loop of the drain line up under the counter, as close to the underside as possible. This will help prevent a clogged sink drain from causing dirty water to gravity-flow back into the DW through its drain line.
An air gap is preferable as activating a disposal while there is a clog in the sink drain can still cause back-flow into the DW.

    Bookmark   April 18, 2011 at 2:27PM
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Randy- if an air gap is still preferable, are there ways to do it other than mounting it next to your faucet? In other words, can you disguise an air gap?

    Bookmark   April 18, 2011 at 2:33PM
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breezygirl can install the air gap and then after inspection have it replaced with a soap dispenser. I don't want the air gap hole and visual mess. My DW would have been fine if it was installed in the old kitchen without an air gap. It bugs me that just because I installed new cabs and tops I have to have the air gap. Don't tell anyone, but that's what I'm planning on doing.

I've also heard of something I think was called a Johnson T. Maybe that's what precious poster was talking about, but I thought it had something to do with a hole on the exterior of the house.

Have you tried the Appliance forum?

    Bookmark   April 18, 2011 at 2:39PM
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Breezy! I won't tell if you don't mind me stealing your idea. I'll check with our plumber to see if we can do that so I can avoid having an extra hole for our soap dispenser (I had planned on one anyway).

I'll cross post on the appliance forum and research this Johnson T...

IN searching for this mysterious Johnson T, I stumbled across this (pretty funny) thread which my earlier search did not show. I wouldn't have known to search for Johnson T and thus wouldn't have found this...

Here is a link that might be useful: pretty helpful/funny

    Bookmark   April 18, 2011 at 2:51PM
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It all depends on your make and model. We have two Bosch 800 dishwashers which did not need air gaps. But we needed an air gap in to pass inspection here in Los Angeles. We had the inspection and then took the air gap out and put in a soap pump. Our plumber made the loop under the sink.

    Bookmark   April 18, 2011 at 3:00PM
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Thanks for that thread. Half of it made my tired eyes glaze over and the other half made me chuckle. I love it when the experts argue.

Steal away! I read someone here doing that more than a year ago when I didn't even know what an air gap was. I knew I did NOT want an extra hole by my sink so I mentally filed that idea away.

    Bookmark   April 18, 2011 at 3:25PM
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Our dishwasher is on an outside wall, so the air gap is just a pipe that goes to the outside of the house with a cap on it. Don't know if that would work for your configuration....

    Bookmark   April 18, 2011 at 3:58PM
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Thanks for the help! Vicki- that would definitely work for my configuration. I'll see what the plumber says. I wanted to check here first so I would know my real options without his opinion swaying his recommendations! :)

    Bookmark   April 18, 2011 at 5:19PM
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you have a few options.

first, you are the one who decides whether to go ahead with an air gap or not. The DW company will not give you their blessing. It's not a model-dependent feature, and there are no DW user manuals that say you don't need it. Strictly speaking, there is wrong information in one of the posts above. ︵

The concept in an air gap, or equivalent, is a fall through open space. The DW drain water gets pumped UP (in the hose) and it has to fall down after that, by gravity. Air is necessary for the fall to occur.

This pumped water falls into your drain prior to a P trap, not downstream of a P trap.

Each option has a few things to know about it.
1. you could loop the hose high under the counter. Then it connects under your sink or into a GD. It gets air from the sink pipe or the GD.
2. you could put the DW hose into a standpipe like your washing machine's standpipe. Before OKing this one, there are things to know about your DWV (drain plumbing) first.
3. ditto above, but reworked to get the needed air from a different place, higher up, like say from somewhere higher than the level of the counter.
4. air gap "nub" on the countertop (it gets needed air from above the counter)

The first one of the four above would not work according to some codes that want you to have any spillage occur at a level higher than the countertop (sink rim). The reason why some codes are written that way is to protect you and public health, because there ARE cases of cross contamination happening when drains get blocked and/or the power is out. Then, someone dies. Or, people get sick. But don't think about this for now while you are learning about plumbing.


    Bookmark   April 18, 2011 at 5:37PM
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We chose our dishwasher (Miele Inspira) specifically because it did not need an air gap. I still haven't gotten around to scheduling our final inspection (augh...should be next week!) so fingers crossed that we will pass without it (since our state code requires it), but we showed the manual to the inspectors who came out at various stages of the rough inspection last winter. While the manual doesn't say the dishwasher "doesn't need it," it does say that there is an air gap built into the machine, and it does not include installation of another air gap in the instructions. This has been interpreted by a number of nearby municipalities as meaning that a second air gap is not needed. Whether ours will go that route too remains to be seen, but the inspectors who looked at the installation directions advised us to follow the instructions because "appliances advance far more quickly than California code" (and our code also says we must follow manufacturer's instructions for appliances). We'll see! YMMV, of course.

    Bookmark   April 18, 2011 at 8:33PM
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The argument that countertop air gaps are always necessary is usually heard from people who are unaware that the United States has an East Coast. I don't know how to cushion the shock of this news, though.

    Bookmark   April 18, 2011 at 8:49PM
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If all else fails, there are air gaps which are built within the soap dispenser. Westbrass makes some. Likely other companies as well.

Here is a link that might be useful: Westbrass

    Bookmark   April 18, 2011 at 9:24PM
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We had mile fax us a statement that an withal is not needed externally in addition to the one built into their machine. One inspector signed off and then in the final the other wouldn't so I ordered an air gap soap dispenser but the plumber didn't show to install so I just stuck it in the never mt hole. We passed inspection. Some inspectors know as much about what they are inspecting as they do about brain surgery.

    Bookmark   April 18, 2011 at 11:43PM
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igloochic that is a great story.

Personally, I think a high loop is OK.


I also like standpipes.

My posting information concerning public health is a help.

The question is, "where will the (contaminated) flow go?"
I think that drains with garbage disposals on them block more often than those without.

Whatever you all decide to do, please do it because of your own mind and understanding.
The more you know, the better it is.

The thread linked to above is a good thread to read.


    Bookmark   April 19, 2011 at 8:44AM
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"The argument that countertop air gaps are always necessary is usually heard from people who are unaware that the United States has an East Coast. I don't know how to cushion the shock of this news, though."

Thank you! This east coaster was mystified the first time she came to this board and heard all the discussion of air gaps.

I've seen plenty of dishwashers in plenty of houses in my 47 years but have yet to see an air gap - or hear of anyone putting one in.

    Bookmark   April 19, 2011 at 9:50AM
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I live on the East Coast and I see them all the time...I guess this is why I am so adamant about avoiding the countertop air gap. No GW-ers probably don't notice, but I think we are all TKO and totally observant.

Thank you everyone for your posts. Very helpful. After reading my kitchen aid brochure for installation, I see that there are two options

1. with air gap
2. without air gap

Theres no mention of a situation/why you could install without an air gap. Davidro- thanks for clarifying that it is not model specific and more personal preference.

I'll speak with the plumber and determine what our true options are. I have no idea what our code stipulates. If the plumber doesn't know, then I guess we have bigger issues than an air gap :)

    Bookmark   April 19, 2011 at 10:57AM
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Marcolo, you crack me up! I grew up in NY and had only been in CA 3 years when we ran into the airgap issue. Fortunately, we live in a city that recognizes manufacturer specs and does not require one as long as the DW says its fine.

Of course finding a plumber that didn't believe that the laws of physics operate differently in the state of CA than in the rest of the universe was more of a challenge.

    Bookmark   April 19, 2011 at 12:00PM
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I've meet with about 7 plumbers during my search for the right one. Only one of them believed that an air gap was essential. The others just said I could do the Johnson tee or the soap dispenser-swap-out-after-inspection trick. I don't live in a big city so maybe old ways of thinking are common around here. I live in Washington so while we're west coast, I've never seen an air gap IRL and never heard of them until I found GW.

    Bookmark   April 19, 2011 at 2:57PM
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