What condition is NOT allowable for single wall vents in a residence?

Single wall vents in a residence are governed by specific installation rules to ensure safety and efficiency. An important factor is that they cannot pass horizontally through walls. The reason for this is primarily related to maintaining the proper venting and preventing the risk of heat buildup or the accumulation of combustion gases within an enclosed space. Horizontal runs can hinder the venting process and could lead to backpressure or potential leaks, which can be hazardous.

On the other hand, conditions like running directly from the appliance to the outside are acceptable as they promote efficient venting without causing any obstruction. Installing in open spaces is also allowable since it helps dissipate heat and allows for the easy passage of combustion byproducts outside. Furthermore, using multiple bends may be permissible as long as the total length and configuration of the vent still comply with local codes and do not significantly restrict airflow.

Overall, ensuring that installation adheres to safety standards is crucial, and passing through walls horizontally is not permitted for single wall vents to mitigate safety risks.