The “air gap” and “high loop” are methods employed in plumbing to prevent backflow of contaminated water into the clean water supply. An air gap establishes a visible physical gap between the water outlet and potential contaminants, making it a highly effective solution.

What Is A Dishwasher High Loop
The air gap and high loop

When it comes to maintaining your dishwasher’s optimal performance, ensuring proper drainage is crucial. Two common methods used to prevent dirty water from flowing back into the dishwasher are the air gap and the high loop.

Understanding the Air Gap and High Loop

What is an Air Gap?

What is a Dishwasher Air Gap?
What is a Dishwasher Air Gap?

An air gap is a physical gap or space between the dishwasher drain hose and the sink drain pipe. It prevents backflow by allowing air to flow into the dishwasher’s drain line, breaking the siphoning effect that could lead to contaminated water entering the dishwasher.

What is a High Loop?

What is a dishwasher high loop and why do you need one?
What Is A Dishwasher High Loop?

A high loop is an alternative method to prevent backflow in your dishwasher. It involves creating a loop in the drain hose that is attached as high as possible under the kitchen sink. This loop raises the drain hose above the level of the sink, acting as a barrier against water flowing back into the dishwasher.

Pros and Cons of Air Gap and High Loop

Air Gap

  • Provides maximum protection against backflow by creating a physical barrier between the dishwasher and sink drain.
  • Meets plumbing code requirements in many regions.
  • Relatively easy to visually inspect for blockages or obstructions.
  • Requires additional installation space above the sink, which may not be ideal for some kitchen layouts.
  • May be more challenging to retrofit into existing plumbing setups.
  • Can be visually unappealing to some homeowners.

High Loop

  • Offers a simpler and cost-effective alternative to the air gap.
  • Does not require additional installation space above the sink.
  • Can be easily incorporated into most dishwasher installations, making it a popular choice for retrofitting.
  • Provides slightly less protection against backflow compared to an air gap.
  • Requires proper installation to ensure the loop is higher than the sink’s flood level rim.
  • May not meet plumbing code requirements in some regions.

Choosing the Right Option for Your Dishwasher

Factors to Consider

  1. Plumbing Code Requirements: Check your local plumbing codes to determine if an air gap or high loop is required in your area.
  2. Space Availability: Assess the space above your sink to determine if there is enough room for an air gap installation.
  3. Existing Setup: Consider the current configuration of your dishwasher and plumbing to determine if a high loop can be easily incorporated.

Installation Steps for a High Loop

Dishwasher Will Not Drain - High Drain Loop Installation
What Is A Dishwasher High Loop
  1. Locate the dishwasher drain hose that connects to the household plumbing.
  2. Fasten the drain hose to the underside of the countertop, creating a loop that reaches at least 32 inches above the floor.
  3. Use a bracket, plumber’s tape, zip ties, or wire to secure the drain hose in place, ensuring it maintains the high loop position.
  4. Avoid puncturing or damaging the drain hose during installation.

Frequently Asked Questions

Can I install an air gap if there is limited space above my sink?

What Are Dishwasher Air Gaps and Are They Necessary
What Is a Dishwasher Air Gap

If space is a constraint, consider opting for a high loop as a viable alternative to the air gap.

Is one option more effective than the other in preventing backflow?

While an air gap provides the highest level of protection, a properly installed high loop can effectively prevent backflow in most situations.

Should I hire a professional plumber for installation?

If you’re unsure about the installation process or need to ensure compliance with local plumbing codes, it’s advisable to seek the services of a professional plumber.


When it comes to preventing backflow in your dishwasher, both the air gap and high loop options offer viable solutions. The air gap provides maximum protection but requires additional space above the sink, while the high loop offers a simpler and more cost-effective alternative. Consider your specific requirements and consult local plumbing codes to determine which option is best for your dishwasher setup.

Key Takeaways

  • An air gap creates a physical barrier between the dishwasher and sink drain, while a high loop raises the drain hose above the sink’s level.
  • Air gaps offer greater protection but require additional space, while high loops are simpler to install and retrofit.
  • Consider plumbing code requirements, available space, and your existing setup to choose between an air gap and a high loop.
  • Install a high loop by securing the drain hose under the countertop, ensuring it reaches at least 32 inches above the floor.

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