A little light reading... http://airgap.com/plumbing_codes.html

Air-gap or anti siphon devices have been part of the code, in some areas, for over 35yrs. and while you may think they are not required in your area, that assumption may be conditional.

Verify with your local building dept.

There are alternative installation methods for DW where the sink and other plumbing are to remain.

Miele was the first to offer DW with a built-in back-flow preventer, which allowed homeowners to petition the building dept. for relief from the requirement.

There are now several appliance mfg. who offer one or both, back-flow preventers on the supply as well as the discharge side of the DW.

Thanks for the reading, justalurker, but it made no sense to me. Will get DH to read through it. If I understood it right, it seems that it's important for those with water softeners which we don't have or need here. Maybe not so much if you don't have one?

snoonyb, it's possible it's code in my area so I should check that out. However, since I've never seen such a gadget in anybody's kitchen in my lifetime, I doubt it or there are a bunch of us not up to code. And nobody has ever brought it up at the plumbing shops when we've redone kitchens in our rentals and have been buying supplies. Seems it would have come up in conversation?

I've had built-in DW's for 30 years without any of the back-up problems mentioned. Maybe we've just been lucky? If the built in back-flow preventers are relatively new, our DW is almost 20 years old so I doubt we have one.

Will continue to try to learn more about this and consider it. I don't want my luck to run out and have a problem in the future.

It is my understanding that an air gap is required by code on any appliance that is connected to potable water and runs to drain. Softener, reverse osmosis, and dishwasher are just a few.

The length of time that one does anything without problems does not reflect on the safety of doing it. The fact that air gaps are code required indicates that there were a sufficient number of incidents to require a code change at some point. Driving for 50 years without having an accident doesn't mean you won't get into one tomorrow.

There are million of people in homes with closed plumbing systems who never had a problem... until the T&P valve on their WH failed and the WH exploded or they were beset with multiple plumbing leaks at faucets and fixtures. Since the 90's code has required thermal expansion devices in all homes that have a closed plumbing system.

Yes, it does sound important. I'm not arguing that. I'm just surprised nobody I know has one and that I'm unaware of any problems caused by not having one. And that plumbing shops have never mentioned it. I will definitely be checking codes and ensuring we do this right. I don't want an expensive disaster.

If it's required on any appliance that runs to drain, like a DW, why isn't it required on washing machines? Don't they run to drain, too? Just curious and trying to understand.

I'm not sure that an air gap is not required on a washing machine. There are air gaps for washing machines.

What I can say is that if I had a dollar for every water softener and RO I have seen that was installed by a licensed plumber that was in blatant violation of code I'd be sitting on a beach somewhere.

When i moved into my house in 95 I experienced all kinds of odd leaks from faucets and burping from the T&P valve on the WH. Called four of the most highly respected plumbers in the area and all four told me I needed a new WH.

After getting fed up replacing seals and cartridges chasing the problem I replaced the T&P valve on the WH. No help. I decided that it had to be a pressure problem and hooked up a pressure gauge to the service line. Showed a reasonable 55 psi. Problem continued. Then I bought a pressure gauge with a tattletale needle and it showed pressure spikes up to 145psi. Far in excess of allowable pressure. Googled thermal expansion and learned a lot. Installed a thermal expansion tank, as code requires, and problem was solved. Haven't replaced a faucet seal or cartridge in 19 years.

Went back to all four plumbers and demanded my money back. Three refunded and I reported the fourth to CID and ultimately got my money back.

Too many tradespeople learned what they learned back when they learned it and then shut off their brains.

Wow, I'm impressed with your ingenuity. I would have taken what the plumbers all said as gospel.

Well, you've certainly given me a lot of things to consider and I'll definitely make sure DH researches this. If we're going to upgrade, we might as well do it right. Thanks!

While building codes, and the adoption thereof can be revenue source for the municipality, the building codes are designed to protect you, from you.

So, I'll pose some conditions, which actually can happen.

The top of a sink is termed as the flood rim, because products rising above the level will flood the adjacent spaces.

Wether the sink rests on top of, even with or below the counter top, the highest point in the installation is the flood rim.

There are essentially 2 acceptable methods of installing a DW.

1. Is with an air gap.
2. Is using the high loop method.

The high loop method involves elevating the DW drain line and supporting it to the highest point possible, prior to attaching it to either a garbage disposal or the waste fitting in the sink tail-piece, just above the trap.

So, with the high loop method, the drain hose is always lower than the flood rim.

Then, in the event of a plumbing back-up, which fills the sink, the potential for waste water back-flowing into the DW exists, if you are unaware of the waste water in the appliance, and you open the door..............

However, if there is also a loss of water pressure, the waste water can then be siphoned from the DW, back into the potable water system.

An air gap would have prevented this.

"What I can say is that if I had a dollar for every water softener and RO I have seen that was installed by a licensed plumber that was in blatant violation of code I'd be sitting on a beach somewhere". Same goes for DW installations.

With respect to snoonyb the HIGH LOOP id NOT an acceptable method of installing a DW although it is commonly done by plumbers and overlooked by inspectors. A competent plumber who understands siphoning back and cross-contamination would look at a high loop and KNOW it will not work cause the hose is lower than the rim of the sink. The question the plumber ponders is, and only if he/she is competent and ethical,... do you want to do it right or get the job done and get paid? We all know the answer.

"... just surprised I'm not seeing them in all of these kitchens, even the high-end ones". The same plumbers install cheap sinks and dishwashers and expensive high end sinks and dishwashers. Air gaps above the sink are often removed and discarded to accommodate sprayers and soap dispensers and RO faucets cause that's easier to do than drill another hole in the sink.

"I don't see an air gap in any of them and they all have DWs."

Here are some this site:
http://ths.gardenweb.com/forums/load/kitchbath/msg121408416585.html?14
http://ths.gardenweb.com/forums/load/kitchbath/msg1214215417634.html?15
http://photos.gardenweb.com/home/galleries/2012/06/backsplash_and_counters.html?cat=kitchens

As I had previously noted, There are now several appliance mfg. who offer one or both, back-flow preventers on the supply as well as the discharge side of the DW.There are also, alternative installation methods for DW where the sink and other plumbing are to remain.

Miele was the first to offer DW with a built-in back-flow preventer, which allowed homeowners to petition the building dept. for relief from the requirement.

justalurker

"the HIGH LOOP id NOT an acceptable method of installing a DW although it is commonly done by plumbers and overlooked by inspectors."

Here is a PDF from bosch;

http://c.shld.net/assets/docs/spin_prod_940234412.pdf

It's a display of what I mentioned.

It also contains a disclaimer for an air gap, where required.

Few inspectors would demand that you be required to change or drill a sink or change or eliminate a sink dispenser, just to facilitate an air gap, over an inconvenience.

You are not required to obtain a permit for an aftermarket DW installation because it does not require either a waste or supply modification, before a trap or shut-off valve.

The original air gaps were constructed from copper, installed through the exterior wall and drained to the ground.

When I install an after market appliance, I always inform the homeowner of the code requirement as well as the potential downside in a sale.

It then becomes incumbent upon the homeowner to do their own risk management.

A clothes washer drains either into a stand pipe or a laundry sink. Both of those constitute an air gap.

Air gap devices for a DW can be hidden in a wall.

A stand pipe is not an air gap. If the washer hose is affixed above the lip of the stand pipe THEN it is an air gap.

Same with a laundry sink. The washer hose must be affixed above the maximum possible level of the water.

The air space between the drain hose and the maximum water level is the AIR in air gap.

"The air space between the drain hose and the maximum water level is the AIR in air gap."

ERGO, an 1-1/4" drain hose inserted into a 2" stand pipe acts as an air gap.

Because water will take the path of least resistance, which is flooding out of the stand pipe, rather than overcoming the air pressure in the washer drain hose created by the remaining water level in the drain hose, below the goose neck.

A drain hose draped or attached into a slop sink acts as an air gap because the hose is higher at the point of entry, than the sink flood rim.

No sir... All the documentation and examples I've seen define an air gap (in plumbing) as a free air space from the end of a vertical drain hose down to above the highest maximum possible level of the water in the receptacle (stand pipe or sink or or floor drain or whatever.

When the end of the drain hose is at or below the maximum possible water level of the receptacle siphoning is possible and that is EXACTLY what an air gap is designed to prevent.

"A drain hose draped or attached into a slop sink..." is NOT higher than the sink flood rim. INTO a slop sink infers the hose is below the sink flood rim. Now if you say ABOVE a slop sink then that IS an acceptable air gap just as a drain hose to a floor drain must be affixed with the hose end ABOVE the rim of the floor drain to be an air gap and not simply stuck into the drain or resting on it..

This post was edited by justalurker on Tue, Dec 16, 14 at 16:25

Amazing.

"When the end of the drain hose is at or below the maximum possible water level of the receptacle siphoning is possible and that is EXACTLY what an air gap is designed to prevent."

Please explain the physics of "siphoning" in a clothes washer, unless two valves and the potable water, all fail simultaneously.

"A drain hose draped or attached into a slop sink..." is NOT higher than the sink flood rim."

Please describe the route that the hose takes to end up in the sink, without being draped over the flood rim.

"INTO a slop sink infers the hose is below the sink flood rim."

Please describe the amount of pressure, the water needs to be under, to both flood over the flood rim, and, overcome the pressure in the hose created by the remaining water in the hose.

Set siphoning aside cause it is a rare occurrence.

The potential problem, and the reason air gaps are required, is not necessarily the WATER but of more concern is the BACTERIA IN THE WATER. If the drain/sink backs up and contacts the appliance's drain hose.

Bacteria can transfer by CONTACT with the appliance's drain hose and migrate into the appliance and colonize there. That will contaminate the potable water. With an AIR gap there can be no contact and therefore no cross-contamination.

"Set siphoning aside cause it is a rare occurrence."

Your logic, not withstanding, the water inlet to a clothes washer is higher than the tub, so that is in and of itself, an air gap.

So, for bacteria to migrate into potable water system, the appliance would have to be submerged, and a total loss of potable water supply pressure and the power loss to the washer with the valves open, in the fill cycle.

I defend your right to endanger your own health and safety but don't endanger the health or safety of innocent bystanders.

Learn about cross-contamination and bacterial colonization.

This post was edited by justalurker on Thu, Dec 18, 14 at 1:45