What condition can lead to condensation forming in a venting system?

Condensation in a venting system can occur when the temperature of the gases being vented is too low. This situation arises because cooler gases can have water vapor that condenses into liquid droplets when they cool below their dew point. If the temperature rise is insufficient, the vent gases may not be hot enough to remain in a gaseous state, leading to moisture accumulation and potential issues such as corrosion or blockages in the venting system.

In contrast, a higher temperature rise keeps the gases well above their dew point, minimizing the risk of condensation. Smaller vent diameters or excessive distances from the appliance can contribute to inefficiencies in venting but primarily affect the pressure and flow of the gases rather than directly causing condensation through temperature issues. Therefore, low-temperature rise is the primary condition leading to condensation in a venting system.