Do I Need An Air Gap For My Dishwasher?

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You have treated yourself to a nice new dishwasher for your kitchen, but you are unsure how to best install it. Do you need an air gap or not? The simple answer is no. You do not need an air gap for your dishwasher, but it is preferable. 

Although you technically do not need an air gap for your dishwasher to work correctly, it is commonly required by law in many places in the world, particularly within the United States.

As such, it is written into plumbing codes to make sure that houses are as safe as possible and that you will never run the risk of cleaning with contaminated water when purchasing a property.

If you are selling your home any time soon, then it is best to check that your dishwasher has an air gap as you may not be able to sell your house without one!

An air gap is not the only method of preventing the recycling of dirty water, and we will explain the alternatives below. The advantage, however, of having an air gap is that they are foolproof. They contain no moving parts and so will always work. There is no part of the fixture that can break or stop working. 

Dishwasher air gaps are also required by plumbing codes in many locations. While air gaps are not the only method of preventing your dishwasher from backflow, they are the only method proven to work under every circumstance. 

Air gaps have no moving parts, so they cannot fail. Water cannot siphon back through an unpressurized gap of air. 

If the drain tube becomes clogged, the dishwasher’s discharge water will spill out of the holes on the air gap’s heading. This means that your clean water supply will always be safe from contamination, even if you have a serious blockage affecting the plumbing in your kitchen.

What is a Dishwasher Air Gap?

A dishwasher air gap is a fixture installed about two inches above your sink that stops used water from reentering into your clean water system. It, therefore, stops contamination, ensuring that your clean water system remains clean. This means that you never run the risk of washing your dishes with wastewater.

This problem can often be diagnosed if, after you have run the dishwasher, there are still streaks on your plates! Unlike other methods of stopping contamination between the water pipes, air gaps are known to be one of the most effective fixtures that you can install in your kitchen. 

Often an air gap will be fitted to a hole that already exists, either in your sink or your countertops. They are an easy solution to the reuse of dirty water as they require little maintenance. Just as you would regularly and routinely clean your dishwasher to keep it in good working order, so too should you clean your air gap. 

How Does Backflow Work?

Backflow is precisely as it sounds. It is the “flowing back” of water from where it came. This means an alternation in the pressure, and the water goes the wrong way through your pipes.

This can mean that instead of the used, dirty water from your dishwasher being pumped out and being discarded, it is mixed into the clean water supply, and then it used to “clean” your dishes! Not ideal! 

One easy way to think of how this works is to think of a clogged sink. If backflow occurs, then the dirty water will go back into the appliance (here dishwasher) because it has no room to go anywhere else. Since there is room in the dishwasher and the water cannot flow forward through the pipe, it goes backward. Hence the term “backflow” was coined.

How does a Dishwasher Air Gap Work?

An air gap is a simple yet effective fixture. It separates two hoses: the one with dirty water and the one leading to the drain. This means that there is no “cross-connection” in plumbing terms. The dirty water cannot contaminate the clean water.

One part of the air gap is fitted to the dishwasher, whereas the other is fitted to the garbage disposal. A pipe carries the used water that goes from the dishwasher up toward the air gap and then down into the second pipe. This second pipe then leads to the disposal of the unwanted, used water.  

Air gaps are so important because they contain holes that cause excess water to flow out into your sink if the drain becomes clogged. This means no backflow as the dirty water will run out into the sink rather than back into the dishwasher, leaving your plates squeaky clean.

If this happens and you notice the overflow of dirty water into your sink, then this is a sign that there is a blockage in your drain pipes and that they need maintenance and probably cleaning.

One simple way to remember how an air gap works is to think of the literal air gap between your tap and your sink. If your sink has a blockage and the water starts to bubble back up the pipe into the sink, then the air gap between the sink and tap means that the dirty water will spill out onto your countertops.

The dirty water will never touch the tap. There is no possible way that your clean water supply (the tap) can be contaminated with the dirty water coming back up into the sink.

What is a Dual Inlet Air Gap?

A dual inlet air gap is two birds one stone solution. It is used when there is more than one appliance that needs an air gap.

For example, if your kitchen contains two dishwashers, then you can use one air gap instead of two. Similarly, if you have a dishwasher and a water filter system, they can also use the same air gap. This means that there is a little plumbing as possible and that your kitchen plumbing can be kept nice and simple. 

Dual inlet air gaps can be easily identified by their shape. Since a normal air gap will only require a connection between two things, the connection will have two leads, making it look like the letter “Y”. However, the dual inlet air gap will require the connection of two appliances to the drain to have three leads.

The inlet plug of a dual inlet air gap can be adapted depending on what you need to use it for. The plug can be used to block one of the internal slots if you only need to use one inlet, either only for a short while or permanently. 

How do I Install a Dishwasher Air Gap?

Luckily, air gaps are a simple fixture to install yourself at home. There is no need to call an expensive plumber! To install a dishwasher air gap, complete the following steps:

  1. Find the air gap hole in your countertop. Typically, most homes will have a hole already cut to install an air gap. Sometimes it is hidden by a cap or cover, which is typically flat. However, if there is no existing hole for the air gap, you will have to cut yourself. If this is the case, then make sure that you create the air gap hole close to the top of the sink so that any water overflow will have as much space as possible. A shallow overflow allowance is pointless. If you are uncomfortable with this process, then you may want to consider hiring an expert.
  2. Connect the drain hose from the dishwasher to the air gap. Make sure that you attach the hose to the small part of the air gap. To connect the two, you can use hose clamps made from stainless steel.
  3. Connect the other drain hose (or disposal hose) to the air gap. Again, make sure to seal the connection using hose clamps. If you need to connect the air gap here to a disposal hose, then you can find the pipe you need sticking out from the side of your disposal unit. However, if there is no hole, then again, this is not a problem. You will need to locate inside the metal plug that is in the tube. This will then allow you to connect the disposal to the air gap.
  4. Push the fixture up through the hole in the countertop. To secure the air gap to your countertop, thread the nut against the air gap threads. You may need an extra pair of hands here as the air gap can rotate as you try to secure it. Tighten with a wrench to make sure that it is entirely secure.
  5. Place the cover back on.
  6. Turn your dishwasher on and check for any issues. These can include leaks.

Can I Install an Air Gap Under the Counter?

Unfortunately, under-the-counter air gaps are not approved. This is because if there were an overflow, then the problem would happen under your sink. In areas where an air gap is required, any air gaps installed under the counter will violate the plumbing code.

If you are installing one to comply with the regulations, make sure you do not use one under the counter as this will not count, and you will have to redo the entire process. 

Make sure that your air gap is above the counter, as this means that any backflow will flow out into your sink and, if need be, onto your countertops. Any overflow under the sink level can cause further problems, which may not be easy to fix!

Dishwasher Air Gap Alternatives

If your area does not require an air gap specifically for your dishwasher, then there are a few alternatives. The first is the “high loop”. This, too, is self-explanatory. A high loop is when the pipe is shaped into an upward arch before reaching the sink drain.

There is no particular fixture for this method; it could even be as simple as securing the pipe with a zip tie or threading it over a hook. For this alternative to be effective, the loop should be placed as close as possible to the cabinet’s bottom. 

Just like an air gap, the high loop’s job is the stop the backflow of dirty water into your system. 

However, it is not as effective as an air gap because it can only deal with mild cases of backflow. This is because if the water reaches the rim of the sink, the water will be able to flow back down the pipe, defeating the high loop’s purpose. 

This is where the air gap is superior and is often standard regulation rather than the high loop.

However, you can only install a high loop if you have at least 32 inches between your floor and the top of the high loop. If you do not have sufficient space, then, unfortunately, you will have no choice but to install an air gap to prevent backflow. 

Another alternative is a dishwasher standpipe. You can find a standpipe above the P-trap, and it is a verticle piece of piping. The P-trap is something that prevents water and odors from going from the drain to your house. 

Standpipes require ventilation. The most common example of a standpipe is a washing machine, which needs to fill and drain water quickly. Unfortunately, standpipes are complicated fixtures. They are significantly more challenging to install than high loops or air gaps and are not nearly as effective.

Therefore, they are not your best option to prevent backflow. Instead, you will be better off installing either an air gap or a high loop.