What issue can arise in a vent pipe with too small of a vertical vent when using an induced draft motor?

When using an induced draft motor, a vertical vent that is too small can lead to pressurization issues within the vent system. The induced draft motor is designed to create a negative pressure, which helps to pull exhaust gases out of the combustion chamber and through the venting system. If the vertical vent is not adequately sized, it can cause resistance to the airflow, inhibiting the motor's ability to effectively expel these gases.

As the motor works harder to overcome this resistance, it can lead to an increase in pressure within the vent. This pressurization can result in improper venting of combustion gases, which may eventually cause backflow or other ventilation problems, creating a hazardous environment. Ensuring that the vertical vent is appropriately sized is crucial to maintaining safe and efficient operation of systems utilizing induced draft motors, as it helps mitigate the risk of pressurization and ensures proper exhaust flow.