In many homes, a dishwasher is a beloved appliance — some families value theirs so much that they give it a name. It saves time, keeps the kitchen free of clutter, and eliminates germs from dishes. Newer dishwashers are environmentally friendly and can use less water than washing dishes by hand.

All of this can be true as long as the dishwasher is installed properly and the water flows in the right direction. The last thing anyone wants to deal with is dirty, contaminated water entering the dishwasher. This is why building codes typically require some type of air gap in the system, and installing a dishwasher air gap is one way to meet this requirement.

What Is a Dishwasher Air Gap?

A dishwasher air gap is a small cylinder fitted with a single tube that splits into two small lines. The device connects the dishwasher to the sink in the kitchen, and its design keeps dirty water coming out of the dishwasher to flow back into the potable water supply. 

What Do Air Gaps Do in a Plumbing System?

Air gaps play an important role in the kitchen plumbing system — keeping wastewater away from the places it shouldn't go. Water enters the dishwasher from the main line, which also supplies water to the sink. It leaves the dishwasher through a waste line that attaches to the sink drain. Without a gap of air in the line, the dirty water leaving the dishwasher (or passing through the sink) could flow back into the dishwasher or worse, it could end up in the clean water pipes, potentially to be accidentally ingested by a person or a pet.

Air Gap vs. High Loop

An air gap is an alternative to a high loop, a term that refers to the shape of the elevated line connecting the dishwater's drain hose to the kitchen sink drain. At its highest point, the hose rises above the sink drain to create the air gap that stops the backflow, similar to the way a P-trap works.

Although a high loop is effective, it's usually not the best option. With this setup, it's still possible for dirty water to flow back into the water supply if a vacuum is created because nothing physically prevents the crossflow.

An air gap does the job better. The cylinder sits on the edge of the sink, usually on the side or corner closest to the dishwasher. The lines extend under the cabinet, where one line connects to the dishwasher and the other connects to the drain or garbage disposal. Between the two hoses is an air gap that physically separates the lines so water can cross over.

When Should You Consider Installing an Air Gap?

People who live in a state or municipality that requires air gaps have no choice and must install the device. If the plumbing is too close to the subfloor, an air gap may be a good idea, even if the building code does not say it's necessary. Homeowners who don't have either of these limitations can decide whether to include one in the kitchen design. However, air gaps tend to do a better job of keeping wastewater out of the dishwasher, which makes them a good choice for everyone.

How Hard Is It to Install an Air Gap?

Replacing an existing air gap is a simple task that handy homeowners can do for themselves. If the job requires cutting a hole in the sink, homeowners may feel more comfortable letting a professional do the work. For those willing to tackle this DIY project, here are the general steps:

1. Disassemble the air gap. Follow the manufacturer's instructions carefully to ensure the air gap works properly.
2. Insert the air gap into the hole in the sink that's closest to the dishwasher.
3. Connect the lines. One line attaches to the disposal, and the other goes to the dishwasher.
4. Secure the lines so they do not disconnect during use.
5. Install the air gap cover above the sink. The vent should face the sink.

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