Information on Exterior Plumbing Stack Vents

Stack vents are vertical plumbing lines inside your walls.

Plumbing stack vents are designed to divert the noxious fumes from your sewage line out of your home. These vents also regulate pressure on the sewage line and prevent sewage gas from backing up through plumbing fixtures. The number of plumbing stack vents that your home requires depends on the quantity and positioning of your home's plumbing fixtures.

Vent Types

There are several basic types of vent used in plumbing lines. Two of the more commonly used types are known as the vent stack and the stack vent. The vent stack is a separate line in your plumbing system that only carries gases. Its only function is to vent gas from plumbing fixtures to the vent on the roof. The stack vent is an extension of the drainage stack, which carries liquid waste from plumbing fixtures.

Design

Plumbing vents are vertical pipes that are connected to the rest of a plumbing system to vent gases and control the amount of pressure in plumbing lines. Vent stacks are typically built above the main horizontal drain line in the basement parallel to the drainage stack. Horizontal pipes with a trap designed to prevent liquid waste from entering the vent stack connect the vent and drainage stacks on each floor of the building. Stack vents are attached at the top of the drainage stack above the horizontal plumbing for the top floor of the building. Vent stacks are more effective in large plumbing systems since they provide multiple avenues for gases to escape from the drainage stack. The pipes used in your home's stack vent should equal at least half the diameter of the drain line to which they are connected.

Purpose

External plumbing vents provide a safe path for the gases in a plumbing system to escape. These vents regulate the pressure in plumbing lines to limit the amount of force exerted on plumbing traps. These traps contain a column of water that is maintained under pressure. This column of water prevents the noxious, flammable gases in the drainage line from entering your home.

Safety

Exterior plumbing vents should extend well above the shingles of your roof. This will ensure that waste gases from your sewage system do not waft back into your home through gaps around the plumbing pipe. If your stack vent becomes obstructed, it can force sewage gas into your home. Covering exterior stack vents with a fine mesh netting or other protective device will prevent debris or nesting animals from plugging your vents.

Energy Efficiency

Stack vents are a common cause of loss of energy efficiency in a home. Old or insufficient weatherstripping around the area where the vent enters and exits your roof will allow air to flow freely into your home. You can seal these gaps cheaply and effectively, using spray foam insulation to fill the gaps around the stack vent.

References

• Georgia Plumbers Trade Association: Venting of Plumbing Systems
• North Dakota State University: Check Your Sewer Vents

Resources

• Iowa Energy: Home Tightening, Insulation and Ventilation