Backflow Protection by Air Gaps

Air Gap Required Locations
1. Use clothes washing and dish-washing machines that contain an air gap device in the machine.
2. Provide an air gap at the discharge point of any relief valve and any relief valve piping (such as a water heater temperature and pressure relief valve discharge pipe).

Air Gap Distance Measurement
1. Measure the air gap distance between the plumbing fixture outlet opening and the flood rim of the fixture or receptor. Measure the fixture outlet opening diameter without the aerator attached. Measure the vertical air gap distance with the aerator attached.

Air Gap Minimum Distances
1. Provide an air gap according to the following table when using an air gap as backflow prevention. Use the away from wall column when the closest edge of the fixture opening is more than (>) three times the effective opening diameter from a single wall and is more than (>) four times the effective opening diameter from two intersecting walls. Use the close to wall column when the closest edge of the fixture outlet effective opening is not more than (≤) three times the effective opening diameter from a single wall and is not more than (≤) four times the effective opening diameter from two intersecting walls.

Example: If the fixture effective opening is ½ inch and the distance to a single sidewall is 1⅝ inches, then the minimum air gap is 1 inch because the distance is more than 3 times the opening size.
Example: If the fixture effective opening is 1 inch and the distance to a single sidewall is 3 inches, then the minimum air gap is 3 inches because the distance is not more than 3 times opening size.
Example: If the fixture effective opening is ½ inch and the distance to either intersecting sidewall is 1⅝ inches, then the minimum air gap is 1½ inches because the distance is not more than 4 times the opening size.
Example: if the fixture effective opening is 1½ inches and the distance to both intersecting sidewalls is 6 inches, then the minimum air gap is 4 ½ inches because the distance is not more than 4 times the opening size.