Why is it important that the ventilation matches the appliance's flue outlet size?

It is crucial that the ventilation matches the appliance's flue outlet size primarily to avoid operational hazards. When the flue outlet size is incorrect, improper venting can lead to issues such as back-drafting, which occurs when combustion gases are drawn back into the living space instead of being expelled outside. This situation can create dangerous conditions including the potential buildup of carbon monoxide, a colorless and odorless gas that poses serious health risks.

Additionally, if the vent size is too small, it may restrict the flow of exhaust gases, leading to increased pressure within the appliance and potentially causing catastrophic failure. Conversely, an oversized vent can allow heat to dissipate too quickly, resulting in inadequate draft and poor appliance performance. Properly matching the flue outlet size ensures that the appliance operates safely and efficiently, safeguarding against these operational hazards.