What happens if a plumbing system is "over-vented"?

When a plumbing system is described as "over-vented," it means that there are more vent pipes or larger vent pipes than necessary for the system. Proper venting is crucial because it allows air to enter the plumbing system, which balances the pressure and facilitates the smooth flow of wastewater. However, excessive venting can lead to problems.

With too much venting, the air entering the system can disrupt the siphonic action that occurs in trap seals. Traps are designed to hold a small amount of water to prevent sewer gases from entering the living space. Over-venting may cause these traps to siphon out too much water or completely empty, leading to situations where sewer gases can escape and inadequate drainage occurs. As a result, fixtures could fail to drain properly, causing backups or other plumbing issues.

This phenomenon emphasizes the need for balanced and adequate venting in a plumbing system, where the venting works in harmony with the drainage to maintain proper function. The other options do not accurately reflect the consequences of over-venting, as they either imply a positive effect on water flow or suggest no impact at all, which overlooks the critical issues of drainage and siphoning that can arise.