Do You Need An Air Gap For A Garbage Disposal?

When it comes to plumbing the handy little appliance hidden beneath your sink, there are a few things to consider. Plumbing codes outline specific rules for various scenarios, including installing a garbage disposal. 

So, when you install the appliance, do you need an air gap? Better yet, what is an air gap, and what does it do? This article answers each of these questions, so continue reading to learn more!

What Is An Air Gap?

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An air gap, which is required in various plumbing installations, is a simple way to prevent contamination of your potable (drinkable) water supply. Once this water leaves the outlet of a fixture (faucet), the contents of the drain line shouldn’t be able to make contact with the water supply. 

The two plumbing systems, one for potable water and the other for waste, should always remain separate. The potable water may become seriously contaminated if they come into contact, also known as a cross-connection. 

Occurrences like these can occur in backflow events, where the difference in pressure in the supply line can pull the contents of the drain line into the clean water supply. 

Air gaps help prevent these cross-connections and contamination by ensuring water and waste are discharged across an unobstructed space, in this case, a gap of air. This gap is located between the fixture outlet and the “flood level rim” of the receptacle (like a sink, floor drain, etc.). 

For example, consider a faucet (outlet) and a sink basin (receptacle). The water leaves the tap and flows across empty air into the basin. If the basin were to stop draining normally and back up to its flood level rim (the top edge of the sink), the dirty water would never reach the faucet, thanks to the space between the two. 

The same concept applies to air gaps in plumbing. The air gap provides a space between the two pipes that guarantees there won’t be any cross-contamination between the two. It offers a vacuum with pressure necessary to ensure water cannot mix with the opposite, like waste water with freshwater or vice versa. 

Do I Need An Air Gap If I Have A Garbage Disposal?

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Garbage disposals require an air gap to prevent cross-connections and contamination that may occur via waste or discharged water. 

The rules may change based on your location, particularly if you have a dishwasher. For example, some areas may allow a direct connection between your dishwasher and garbage disposal. In this case, you would need to use the ‘high loop method’ instead of the air gap.

What Happens If I Don’t Put An Air Gap With My Garbage Disposal?

If you don’t use an air gap with your garbage disposal, you may deal with a contaminated water supply. Depending on where the cross-connection occurs, the dirty water may contain things that can make you and your loved ones sick. 

So, it’s essential to follow the guidelines regarding air gaps with your garbage disposal or dishwasher.

Where Is The Air Gap On A Garbage Disposal?

The proper placement of an air gap for a garbage disposal depends on your plumbing setup. It should be situated where it can intervene between any interconnecting clean or dirty water lines. If you’re not sure where the correct placement should be, contact a professional for assistance. 

For the most part, plumbing codes require a minimum two-inch air gap. However, regulations may vary based on the particular scenario. For example, discharge or supply lines that exceed one inch in diameter will need a minimum gap distance of twice the pipe’s diameter. 

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So, if the pipe is two inches in diameter, it would need a four-inch air gap. Make sure you check with local regulations and restrictions to determine the best course of action in your area. 

Air Gap Rules With A Dishwasher And Garbage Disposal

If you have a dishwasher, the regulations change slightly. Since most homes have dishwashers, many people need to take an alternative route with the plumbing when they install a garbage disposal. It’s imperative to correctly install and connect the dishwasher and garbage disposal to avoid issues with cross-connections and contamination.

You shouldn’t bypass the garbage disposal if it’s present when you’re plumbing the dishwasher. In this particular scenario, the dishwasher drain line should run down from the air gap (or high loop) and connect to the side nipple on the garbage disposal, where it is connected with a hose clamp. 

After you finish installing the air gap and connecting the necessary plumbing, run a cycle on the dishwasher to make sure everything is working correctly. You’ll know pretty quickly if you messed up with the plumbing, as you might end up with a mess on your hands. 

Of course, rules may vary from one location to the next, so make sure you double-check. Or, if you’re not an avid DIYer who regularly tackles plumbing projects, consider having a trained professional handle the plumbing and installation. 

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