What a vent does and why it matters
Water moving down a pipe pushes air ahead of it and leaves a vacuum behind it. A vent lets air in so the water flows smoothly and the trap seals stay full. Without a vent, water can siphon the trap dry, and sewer gas then enters the room.
Plumbing codes such as the Uniform Plumbing Code and the International Plumbing Code require each fixture to be vented. How a house is vented varies, but most have one or more pipes that rise through the roof.
Symptoms that point to the vent
No single symptom proves a vent problem. A pattern does.
| Symptom | What it suggests | What to try |
|---|---|---|
| Gurgling from several drains | Air is being pulled through traps | Check the roof vent. |
| Slow drains in more than one fixture | Poor air supply or a main line clog | Camera or cable check. |
| Sewer smell indoors | Trap seal siphoned or vent leak | Run water in unused drains and call. |
| Toilet bubbles when another fixture drains | Air is trying to escape | Check vent and main line. |
| Drain empties noisily | Vacuum in the line | Look for a blocked vent. |
These signs overlap with a blocked main line. A sewer camera inspection sorts out which one you have.
What blocks a roof vent
Most vent blockages are above the roof, where debris can enter an open pipe.
- Leaves, seed pods and windblown trash that settle in the pipe opening.
- A bird or rodent nest built in the top of the pipe.
- A frozen or crushed section, which is rare in Arizona.
- Roof work that left a cap, flashing or debris over the opening.
- A crushed or disconnected pipe in the attic.
Drains gurgling in several fixtures?
Call us with which drains act up and when. We will tell you whether the vent or the main line is the likely cause.
Call (480) 741-9332Safe checks before you call
Do not climb onto a roof unless you are trained and equipped. The safest check starts on the ground.
- Run the fixtures.Note which drains gurgle or slow and which do not.
- Look from the ground.Use binoculars to see whether the vent pipes have caps or nests at the top.
- Flush and watch.Flush the toilet and see whether other fixtures bubble.
- Check the cleanout.If an outside cleanout fills with water, the problem is the main line and not the vent.
- Call for help.If symptoms remain, a plumber can run a camera and test the vent.
How a plumber clears and tests a vent
A plumber reaches the vent from the roof or the attic. A small cable or a stream of water clears debris. A camera or a smoke test confirms the pipe is open and sound.
If the vent is clear and the symptoms remain, the main line is the next suspect. Our drain cleaning service covers that case, and sewer line repair covers a line that has failed.
Vents and older Florence buildings
Buildings in the Florence Townsite Historic District, which the National Register of Historic Places listed on October 26, 1982, have been remodeled many times. Vents added during later remodels may be undersized or tied in unusually. A camera and a smoke test show the real layout before anyone cuts into a wall.
Vent problems that start inside the walls
Not every vent problem is on the roof. A vent can also fail inside the house, where it cannot be seen.
- A section of vent pipe crushed during a remodel.
- A joint that separated in the attic and now leaks gas or loses air.
- A vent tied into a drain that clogs, which turns the vent into a sump.
- A vent with a long horizontal run that traps moisture.
These faults show up as smells in the attic, damp insulation or gurgling with a clear roof vent. A plumber checks them with a camera and a smoke test, which pushes harmless smoke through the system and shows where it escapes.
Why sewer smells deserve attention
Sewer gas contains hydrogen sulfide and methane. Small amounts smell bad and can cause headaches. Methane is flammable. A persistent smell is a reason to find the source, not to mask it.
Start with the simple fix. Run water in every drain for a minute, including the guest bath and the floor drain, since a dry trap lets gas through. If the smell stays, the problem is a vent, a failed seal or a cracked pipe. If you ever smell gas that seems like natural gas, leave and call the gas utility.
Local note: who to ask about vent changes
If a fix means adding or moving a vent, ask the building department that covers your address. The Town of Florence Community Development Department is at 224 W. 20th Street, phone 520-868-7575. Pinal County Building Safety is at 85 N Florence Street, First Floor, Florence AZ 85132, phone 520-509-3555.
Roof work should also be done safely. Summer roof surfaces in central Arizona get very hot, so schedule work early in the day or hire a roofer for access. We can coordinate when a vent repair needs a roof visit.
We take vent and drain calls in Coolidge and San Tan Valley too.
Source type: Town of Florence and Pinal County Building Safety contact pages (local government). Office details are given according to each agency's own contact page.
Questions readers ask
Yes. A blocked vent can pull water out of traps, which lets sewer gas into the room.
It rarely damages pipes, but it makes drains work poorly and can let gas enter the house.
A clog usually affects one or a few fixtures with standing water. A vent problem causes gurgling and slow flow at several.
Remodels over many decades can leave odd layouts. A camera and smoke test show what is actually there.