On a horizontal branch, what is the maximum distance from the fixture opening that a vent can be connected?

The maximum distance from the fixture opening that a vent can be connected on a horizontal branch is 2 feet. This regulation is put in place to ensure that the vent is effective enough to allow for the proper escape of sewer gases and to maintain atmospheric pressure within the drainage system. Connecting the vent too far from the fixture can lead to pressure fluctuations and potential siphoning of the trap, which may result in foul odors escaping into the living space or possible blockages in the drainage system.

The specified distance of 2 feet strikes a balance between practical installation and the need for effective venting. It allows enough room for installation while ensuring that the vent remains functional. Distances greater than 2 feet could impede the vent's ability to function correctly, thus compromising the integrity of the plumbing system.