Why is natural ventilation not always sufficient for combustion appliances?

Natural ventilation systems rely on the movement of air caused by natural forces, such as wind and temperature differences. However, these systems can be significantly affected by changes in outdoor air pressure, which can disrupt the flow of air needed for combustion. When outdoor air pressure fluctuates, it may lead to insufficient air being drawn into the combustion appliance. This lack of adequate air can hinder the proper functioning of gas appliances, potentially leading to incomplete combustion, safety hazards, and the buildup of dangerous gases like carbon monoxide.

In scenarios where outdoor air pressure is significantly lower than the pressure inside a building, the natural ventilation may fail to deliver enough air needed for efficient fuel combustion. Maintaining a consistent and safe operation of combustion appliances thus often requires mechanical ventilation systems to ensure that adequate air is supplied, regardless of external weather conditions.