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Plumbing 101: Figuring Out if Your Plumbing is Vented

November 24, 2020

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Before making plumbing repairs or installing new pipes, it’s vital for a homeowner to ask, “How do I know if my plumbing is vented?” Vents help remove solid waste from pipes while also regulating air pressure, which controls water flow. Every drain in your home’s plumbing, including kitchen sinks, toilets, and showers, all need venting!

To ensure plumbing repairs or new plumbing installation perform as expected, note some vital tips about plumbing vents including how to know if the plumbing is vented, what vents do, what happens when your home isn’t vented properly, and how to clear clogged vents. Be sure to discuss any questions you have with a plumber near you, and always leave plumbing work outside your area of expertise to the pros as well!

How Do I Know If My Plumbing Is Vented?

There are a few ways to check if your home’s toilets are vented properly. First, start with the pipes under the bathroom sink and pull the protective wall ring away from the wall itself; shine a light into that hole in the drywall. If you cannot see the pipes behind the wall through that hole, shave or trim a slight bit of drywall around the pipe for a better opening.

If you see a vertical pipe running upwards from the sink pipe, where that pipe meets the drainpipe, this is probably the vent pipe. That single vent is typically sufficient for a standard bathroom with a toilet, sink, and tub.

If you cannot access the pipes under the sink or see behind the drywall clearly, your next choice is to head to the attic. Check for a two-inch pipe running vertically, above the home’s bathroom, which would be the bathroom’s vent pipe. That vertical pipe should connect to a three-inch or four-inch main vent pipe, also running vertically to the home’s roof.

In homes where the main vent pipe is located on the opposite side of the home than the bathroom, that two-inch pipe might run directly to the roof. There might also be other vent pipes connected to it, as plumbers try to connect as many vent pipes as possible, to avoid excessive roof penetrations or openings needed for those vents.

Your last option for checking if your home is vented properly is inspecting the home’s roof vent, and you’ll need an assistant for this task! First, ensure everyone in the home refrains from using any water or plumbing fixtures, including sinks and washing machines, while you try this simple trick.

Next, while your assistant stays inside the home’s bathroom, head to the roof and find a three-inch or four-inch pipe stack, typically uncovered. Have your assistant flush the toilet and note if you can hear the sound of water running inside that pipe. If so, your home’s plumbing is probably vented properly.

What Happens When Plumbing Is Not Vented?

To better understand what happens when plumbing is not vented, it’s helpful to know a vent pipe’s function in the first place! Waste and water pipes are angled downward slightly, so water moves through those pipes by the use of gravity, but that water still needs a bit of added help to move through the plumbing properly. Vent pipes help regulate air pressure; an increase in air pressure helps push water and waste material through plumbing pipes more easily.

To illustrate how this works, imagine turning a bottle of liquid upside down. That liquid will run out the open end of the bottle, but usually somewhat slowly. If you poke a hole in the bottle, that air pressure in the bottle pushes the liquid so it then drains more quickly. In the same way, without vent pipes, your home’s sinks, tubs, and toilets would slow down and not drain properly, or even need some type of siphoning system to literally pull water and waste through pipes!

Poorly-vented drain lines don’t allow water to run freely, leading to clogs and, in turn, backed-up toilets and overflowing drains. Clogs also put pressure on pipes and connectors, leading to leaks, burst pipes, water damage and wood rot, and an increased risk of mold growth in the home!

How Do You Tell If You Have a Clogged Plumbing Vent?

As with all your home’s plumbing fixtures, simply having a vent pipe is not sufficient for ensuring your home’s plumbing is working properly! Clogged vent pipes reduce air pressure in the pipes, which then reduce water flow, increasing the risk of solid waste clogs.

Slow-moving drains are one common sign of clogged vent pipes; as water moves slowly through the home’s plumbing, it will drain out of a sink or tub just as slowly! Gurgling sounds from sink drains and toilets as well as bubbling toilet water when it’s flushed also indicate a lack of proper airflow and air pressure in the pipes, typically the result of clogged vent pipes.

Along with regulating air pressure, vent pipes pull unpleasant odors from the home’s plumbing system. If you notice sewer odors in the home and especially if you can tell that they’re originating from an empty toilet or sink, this might indicate a clogged vent pipe.

Clearing Out Your Clogged Plumbing Vent Pipe

If you suspect a clogged vent pipe in your home, one quick fix is to have someone stay in the home’s bathroom while you head back onto the roof; put your palm over the vent pipe, blocking its airflow, while your assistant flushes the toilet. This lack of air pressure might form a vacuum in the pipes that pulls the clogged materials through, clearing the clog.

If this doesn’t fix the clog, try electrician’s fish tape. This tape resembles a plumbing snake but is far smaller and easier to manage; electricians use this tape to install wiring behind a home’s walls. Feed the fish tape into the vent pipe and reel it in; repeat this process a few times, as needed, to remove that clog.

For persistent clogs, try a garden hose to flush out debris. If this doesn’t work, avoid high-pressure equipment, a plumber’s snake, drain cleaner, and other harsh fixes that often cause more damage! Call a plumbing company near you to address a clogged vent pipe as needed.

Does Every Toilet Need a Vent Pipe?

Since plumbers try to avoid creating unnecessary holes in a home’s roof and will connect as many vent pipes together when possible, you might wonder if every toilet then needs a vent pipe itself. The short answer is that every toilet needs its own connection to a vent pipe or stack, but not necessarily its own individual vent pipe that goes directly to the home’s roof.

If two toilets are on the same side of the house, they can be connected to the same vent stack. That stack might be connected to the home’s main vent stack or it might vent out the home’s roof directly. For toilets located on opposite sides of the home, they will usually require their own vent or connection to a nearby vent stack.

Does a Plumbing Vent Have to Go Through the Roof?

A vent pipe can connect through an exterior wall but it must still extend over the top of the roof. This is to regulate air pressure in those pipes and keep sewer gases and odors from wafting back into a structure as well. To do both, the vent pipe must then stand a good foot above the roof and be located away from windows or doors of both your home and adjacent buildings.

If you’re performing your own plumbing repairs or installation, you can use long-sweep elbow pipes to direct the pipe away from the wall and then upward, higher than the home’s roof. Ensure you choose an exterior wall away from attic windows, and free of obstructions such as tree branches and overhead wires.

Does a Vent Pipe Have to Go Straight Up?

Inside the home, behind its walls, does a vent pipe have to go straight up? This is a vital question if you’re trying to relocate the home’s plumbing and want to work the vent pipe or other fixtures around certain obstructions.

Remember that vent pipes are connected to water pipes; in turn, if a vent pipe doesn’t go straight up, it must be connected at an angle that keeps water from backing up into the pipe. For new vent pipes or if you’re relocating a vent pipe, ensure it sits at no less than a 45-degree angle from horizontal, to keep water from flowing into that pipe.

bathroom plumbing in Watertown

How Far Can a Toilet Be From a Vent?

Regulations for toilets, vents, and all other plumbing fixtures and features and their locations are set by state governments. There are two main plumbing codes in the United States followed by the states; the International Plumbing Code (IPC) and the Uniform Plumbing Code (UPC).

IPC regulations state that there is no set distance for a toilet from a vent, while the UPC sets a distance limit at six feet. To find out which codes your state follows and ensure you’re up-to-date on any changes, call your state or county licensing office that issues building permits, as they can advise you.

Watertown Plumbing & Heating is proud to present this information to our readers and especially proud of the work offered by our plumbing service contractors. If you’re still wondering, how do I know if my plumbing is vented, or have any other plumbing-related questions, call us today! 

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