Is A High Loop the Same as An Air Gap?

Can You Permanently Plumb A Portable Dishwasher?

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Is A High Loop the Same as An Air Gap?

An air gap is a mechanical vent in plumbing fixtures such as sinks, baths, and concession stand water dispensers. It provides an air barrier between the drain pipe carrying sewage or wastewater and the water supply.

No, A high loop and an air gap are not the same, and they serve different purposes in plumbing systems.

Here are some differences between the two:

1. Function

The primary function of a high loop is to prevent the backflow of wastewater from an appliance, such as a sink or dishwasher, into the clean water supply. It achieves this by creating a loop in the drain hose to break the siphoning effect and block any potential contamination from flowing backward.

The air gap also creates a visible and unobstructed gap between the appliance’s water outlet and the plumbing system.

It allows air to enter the plumbing system, and if there is a drop in water pressure, the wastewater will be discharged through the gap rather than flowing back into the clean water supply.

2. Design and Installation

A high loop is implemented by raising an appliance’s drain hose above the sink’s flood-level rim or the dishwasher’s highest water level.

You can achieve this by attaching the drain hose to the countertop’s underside or sink before connecting it to the plumbing system. 

A high loop occurs by raising the drain hose above the sink’s or dishwasher’s flood-level rim.

An air gap is typically an add-on device that has to be installed between the appliance and the plumbing fixture. Depending on the design of your plumbing system, an air gap can be installed at different points and levels.

3. Maintenance

Maintenance of a high loop is simple, as you only have to check for leaks and replace hoses when needed.

You may not even need to do this; the appliance manufacturer will most likely provide a guide on how to check for leaks and perform maintenance.

Does A Backflow Preventer Reduce Water Pressure?

Air gaps are more complex to maintain as you must regularly inspect their condition and clear blockages. Air gaps are also made of materials that can deteriorate over time, so you must replace them periodically.

What is a Dishwasher Air-Gap or High Loop?

A dishwasher air gap and a high loop are two different methods to prevent wastewater backflow from a sink into a dishwasher.

They are designed to ensure a dishwasher’s sanitary operation and comply with plumbing codes and regulations.

This prevents the backflow of water into the kitchen faucet or outlet, depending on how it is installed. Dishwashers are vented on one side, but usually, they are vented on both sides.

A dishwasher might be connected to a sink, but there would not likely be a drain if it is a pressure-less model. Because the dishwasher must boast venting, the vent connection must always remain open.

Therefore, there must be no backflow of wastewater into the dishwasher or the drain line or tub.

A high loop is a piping section connecting the dishwasher and the sink drain line installed above the countertop. A dishwasher will have a high loop instead .

They are mostly used on older dishwashers and in buildings with existing plumbing. Because new washing machines are vented on both sides, modern dishwashers do not require air gaps or high loops.

How Do You Know If You Need An Air Gap?

1. Local Plumbing Codes

The local plumbing codes specify the minimum distance between a fixture drain and the building’s sewer or waste discharge pipe. Commonly, this distance would be at most 100 feet.

2. Type of Appliance or System

For direct discharge appliances or systems, such as a dishwasher or laundry, the building’s plumbing system is sized to handle the discharge. In such cases, you can add an air gap without affecting the building’s size or overall operation.

3. Designated Wastewater System

In some jurisdictions, buildings that discharge wastewater directly to a designated wastewater system (such as public sewers) may be exempt from the requirement for an air gap.

Such buildings are designed and constructed according to local codes and standards.

4. Building’s Use

In some cases, the type of use of the building (for example, commercial versus residential) can affect the requirement for an air gap.

5. Type of Waste

The nature and volume of waste a building produces can also affect whether an air gap is required.

For example, a small apartment building would likely not need an air gap if it only produces wastewater on a small scale (such as the water and wastewater from two kitchens).

Is High Loop Better Than Air Gap?

High LoopAir Gap
PurposePrevents wastewater from flowing back into the sink or dishwasher in case of a clog or backflow,
InstallationRequires raising the drain pipe to a specific height above the drain outlet, usually secured with a strap or bracket.
EfficiencyProvides a good level of backflow prevention.
CostRelatively affordable, as it involves adjusting the height of the existing plumbing.
Space RequirementRequires sufficient vertical space under the sink to accommodate the raised drain pipe.
Code ComplianceComplies with plumbing codes in many regions, as it is an accepted method of backflow prevention.

What Size Should The Air Gap Be?

Air Gap TypeTypical Size Range (Inches)
Thermal Insulation20 – 50
Acoustic Insulation50 – 100
Electrical Insulation0.5 – 2
Ventilation Gap5 – 10
Moisture Barrier1 – 3
Structural Air Gap100 – 200

Do I Need An Air Gap If I Don’t Have A Garbage Disposal?

Yes! An air gap serves as an added layer of protection against backflow. It behaves as a physical barrier between the drain line and the water supply, preventing any potential contamination from entering your plumbing system.

Therefore, it’s advisable to install an air gap, regardless of whether you have a garbage disposal or not, to comply with local building codes and ensure the safety of your plumbing system.

Although they are called air gaps, water flows through them (remember, the pipe carries waste water away from the drain). Even a few ML of water can contaminate a ton of drinking water.

A typical air gap always has 0.5 to 1-1/2 inches of water flowing through it. The air gap is usually sealed using a rubber gasket attached to the drain and water supply pipes.

If the drain line loses pressure, it will not allow water to flow into the air gap. The air gap has no moving parts, and it’s unnecessary to backflush them as they are often called.

Most air gaps are installed under the sink. Install yours in a different location if your plumbing is not directly below your sink.

Can You Permanently Plumb A Portable Dishwasher?

Inspect the drain regularly for obstructions, debris, or deterioration. A clogged air gap may cause a pressure drop, and there is little you can do about it once it has occurred.

It’s common for water to collect on the bottom of an air gap and in cracks around fittings and other places where they make contact with each other.

Why Do You Need A Loop Vent?

1. Airflow

A loop vent is installed to provide airflow during a drawdown. When you turn on the tap, the air is drawn down the pipe and into your house’s pipes, which makes room for water.

The loop vent will act as a backup system if this drawdown process continues for an extended time.

2. Air Admittance Valve (AAV)

A loop vent is installed to avoid needing an Air Admittance Valve in each fixture.

As of today, the code does not require an AAV to be installed unless there is a vent separating the fixture from its branch drain (typically a branch from the horizontal drain that runs through a wall).

This happens most often in new construction in exterior utility buildings, as they rarely connect directly to the main building’s plumbing.

3. Low Water Pressure

A loop vent will help if a fixture has low pressure (a potential sign of a problem).

4. New Construction

When fixtures are installed after the plumbing rough-in, you can use a loop vent to ensure adequate airflow in each pipe back to the Vent Stack. You may need to move or add vents, so ensure you work with an experienced plumber.

5. Indirect Fixtures

With new construction, fixtures and light fixtures may be installed in a manner that does not provide adequate ventilation to the Vent Stack. A loop vent will help prevent water from being drawn into the pipes.

A loop vent is the answer if you have any of these conditions. The code requires that plumbing vents be installed so the Vent Stack has room to operate properly with the bathroom’s plumbing.

What Is The Difference Between Air Gap And Non-Air Gap?

FeatureAir GapNon-Air Gap
PresenceContains empty spaceDoes not contain empty space
FunctionProvides insulation, ventilation, or separation.It provides a continuous barrier.
Material PropertiesNo direct contact between two surfaces.Direct contact between two surfaces.
ApplicationsThermal insulation, acoustic insulation.Solid walls, barriers, or structures.

What Is the Easiest Way to Prevent Backflow?

The easiest way to prevent backflow is by using a backflow preventer, also known as a backflow preventer valve or backflow preventer device.

The preventer is a mechanical device that allows the flow of water on one direction while preventing them from flowing backward, thereby preventing backflow.

A backflow preventer valve consists of two chambers, one for water entering from the upstream source, such as a municipal water supply, and the other for water flowing in reverse to the municipal supply.

A check/gate valve separates the two chambers, allowing only flow in one direction.

If a pressure difference develops between the two chambers, the check/gate valve opens, allowing flow from higher to lower pressure until equalization.

Once equalization has occurred, the check/gate valve closes and prevents flow in the reverse direction.

Your plumber can design the check/gate valve to close when a predetermined pressure difference is reached, or it can be designed to close at a certain time interval.

Backflow preventers also have an overflow chamber connected to the downstream piping so that if there is ever a rupture in the line leading to the backflow preventer, any water normally flowing backward would go into this overflow chamber instead.

Does Every Drain Need A Vent?

Yes! The venting system helps maintain the proper functioning of the plumbing system by preventing trap siphonage, equalizing pressure, and removing sewer gases.

Without a vent, several issues can arise:

1. Trap Siphonage: Water flowing down a drain can create a siphoning effect that pulls water out of the trap. The trap holds water to prevent sewer gases from entering the building.

If the trap loses its water seal, odorous gases can enter the living space. Vents provide the necessary air pressure to prevent siphonage and maintain the water seal.

2. Slow Drainage and Gurgling Sounds: Draining water can create negative pressure without proper venting, leading to slow drainage and gurgling sounds.

Vents allow air to enter the system, equalizing the pressure and ensuring smooth drainage.

3. Sewer Gas Buildup: Vents serve as an escape route for sewer gases, allowing them safely vent out of the building through the plumbing system’s vent stack.

This helps maintain a healthy and odor-free environment within the living space.

4. Odor Complaints: Poor venting can cause sewer odors to build up in the living space. Once the system has been ventilated, odors of sewer gases will dissipate.

5. Structural Damage: If not handled professionally, improper venting can cause structural damage to plumbing systems and piping. This can result in leaks, blockages, and other costly repairs.


Air gaps in plumbing systems are crucial in maintaining the correct pressure, particularly when you have an air gap loop.

In all cases, the air gap or non-air gap loop will help keep your plumbing system safe regarding water pressure and sewage gas buildup.


Hi! I I faced many questions from customers about different products, and there was hardly any help on the internet. After learning all the things about these products as a manager the hard way, I decided to start a blog and help other people.

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