An air gap is a physical, vertical separation between a water supply outlet and the flood-level rim of a receiving vessel. It acts as a safety barrier to prevent contaminated wastewater from siphoning back into the potable water supply.
The distance of an air gap serving indirect waste piping one inch or less in diameter and a receptor shall be at least twice the diameter of the indirect waste piping. The distance of an air gap between indirect waste piping larger than one inch in diameter and a receptor shall not be less than 2 inches.
The minimum separation for an air gap in plumbing is 1 inch (2.54 cm) or twice the diameter of the supply pipe—whichever distance is greater.
You can technically install a dishwasher without a countertop air gap, provided you use a high loop in the drain hose. However, an air gap may be legally required by your local plumbing code.
Consequently, the air gap is usually installed on the countertop, either near or as part of the kitchen sink. It should be placed close enough to the sink that any water draining through the air gap vents goes into the sink rather than the counter.
The "135-degree rule" in plumbing states that the total (aggregate) horizontal change in direction for a drainage pipe—specifically trap arms—cannot exceed 135 degrees between the P-trap and the vent. Exceeding 135 degrees (such as using three 45-degree bends or a 90 and two 45s) requires a cleanout because sharp turns hinder flow and cause clogs.
Dishwasher air gaps are required by plumbing code in California, Washington, Hawaii, and Minnesota. While these specific states mandate an air gap to prevent contaminated water from siphoning back into the dishwasher, the vast majority of other states permit alternative, un-obtrusive setups like the high loop.
Because it's impossible for water to flow back through an unpressurized gap of air, the air gap can prevent water from being siphoned out while the dishwasher is in use, and helps keep dirty, used water from re-entering the unit.
6 Dishwasher Air Gap Alternatives
Installing a dishwasher air gap prevents contaminated sink water from backing up into your dishwasher. It is typically mounted on the sink deck or countertop to the far left of your main faucet.
If your sink does not have an air gap for your dishwasher, you must create a "high loop" in the dishwasher drain hose. Without an air gap or a high loop, contaminated wastewater from a clogged sink can flow backward and siphon into your dishwasher.
The standard hole size required for a dishwasher air gap is 𝟏𝟑𝟖 inches (1.375"). This diameter allows the threaded body to pass through the sink deck or countertop while leaving enough room to securely tighten the mounting nut from underneath.
A dishwasher air gap prevents this from happening by ensuring that the water flows in one direction: out of the dishwasher and into the garbage disposal. If you don't have an air gap, have one installed for enhanced hygiene and plumbing safety.
An “approved air gap” shall be at least twice the diameter of the supply pipe measured vertically above the overflow rim of the receiving vessel; in no case less than 1 inch (2.54 cm).
To airgap a computer, disconnect it from all networks (Wi-Fi, Ethernet, Bluetooth) and restrict physical access to prevent unauthorized connections. Avoid using external devices like USBs unless they're screened to prevent malware transfer.
Whether you need an air gap depends entirely on your local plumbing codes and how your drain hose is set up.
> Federal efficiency standards transformed dishwashers into marathon cleaners. Modern machines take 2.5 to 4 hours per cycle—a far cry from the quick turnarounds families actually need.
No. A high loop involves routing the dishwasher drain hose higher under the sink to reduce the chance of backflow. While it can help in some situations, it does not provide the same level of protection as an air gap and may not meet plumbing code requirements in all areas.
Modern dishwashers do not strictly require an air gap to function, but whether you can legally remove one depends entirely on your local plumbing code.
An air gap prevents contamination and protects health.
If negative pressure occurs in the water system, contaminated water can be pulled back into the drinking water supply line, which is known as “backflow.” Proper design, like an air gap, can prevent backflow.
You can technically install a dishwasher without a countertop air gap, provided you use a high loop in the drain hose. However, an air gap may be legally required by your local plumbing code.
The most common and effective alternative to a countertop dishwasher air gap is the high loop drain hose. By routing the dishwasher drain hose as high as possible under the sink cabinet (securing it just beneath the countertop) before it connects to the garbage disposal, gravity naturally prevents dirty sink water from flowing backward into the dishwasher.
You can by-pass the air-gap on any of the Premier Air-Gap Faucets. Before beginning the air-gap bypass, you will need to check the air pressure in your tank and ensure the ASOV is functioning properly.
No, a dishwasher air gap cannot be installed completely under the sink. For an air gap to function properly and prevent wastewater from backing up into your dishwasher, it must be mounted above the flood rim of your sink. This typically means installing it on your countertop or sink deck.