What Is the Maximum Distance a Plumbing Vent Can Be From a Fixture?

The plumbing vent extends through the roof of the house and allows air and sewer gas to exit the waste water system.

Size of Pipe

This vent allows the air pressure in the system to equalize as water is introduced by draining sinks, tubs or flushing toilets. The proper placement of the vent within the home plumbing system provides for a smooth flow of waste water without gurgling sounds and prevents possible sewer gas infiltration into the living quarters of the home.

The size of the waste water pipe determines the maximum distance the vent can be located from the plumbing fixture. Small pipes, pipes 1 1/4 inches in diameter, require the vent pipe be within 30 inches of the plumbing fixture. A pipe of this size supports a single fixture such as a sink or tub. On the other end of the spectrum, a 4-inch waste water pipe can be placed up to 10 feet from the fixture. This size of pipe is used in multiple dwelling or commercial buildings and can support up to 216 fixtures.

Measure From the Trap

The horizontal distance is measured from the vertical vent pipe to the closest portion of the P-trap. The trap commonly sits directly under the plumbing fixture or drain and may be further from the vent pipe than the edge of the plumbing fixture.

Vent Specifications

The small, 1 1/4 inch, waste water pipes require the same diameter of vent pipe. The larger waste water pipes can use slightly smaller vent pipes. A 4-inch waste water pipe can be vented with a 3-inch pipe. The vent pipe must extend at least 6 inches, but no more than 12 inches, above the roof deck.

Vent Safety

Drain vents do occasionally become plugged. This can cause gurgling sounds from the plumbing fixtures and slow drainage of water. The most common cause of plugged vents is ice accumulation during cold winter weather. The air rising through the vent is warm and moist. If it begins to freeze before it exits the vent stack the ice crystals within the vent pipe can close the opening.

About the Author

Keith Allen, a 1979 graduate of Valley City State College, has worked at a variety of jobs including computer operator, medical clinic manager, radio talk show host and potato sorter. For over five years he has worked as a newspaper reporter and historic researcher. His works have appeared in regional newspapers in North Dakota and in "North Dakota Horizons" and "Cowboys and Indians" magazines.