Which of the following is essential for ventilation in space with combustion appliances?

Natural air intake is essential for ventilation in spaces with combustion appliances because it ensures that there is a continuous supply of fresh air for the combustion process. Combustion appliances require adequate oxygen to burn fuel efficiently and safely. Without natural air intake, the availability of oxygen may diminish, leading to incomplete combustion, which can produce harmful gases such as carbon monoxide. Additionally, proper ventilation helps to remove exhaust gases safely from the space, maintaining air quality and safety.

While air circulation fans can aid in improving air distribution, they do not directly provide the fresh air needed for combustion. Sealed duct systems and closed-loop ventilation systems may restrict the supply of fresh air necessary for appliances that rely on combustion, which contradicts the need for adequate ventilation to support safe operation. Therefore, relying on natural air intake is critical in ensuring that combustion appliances operate effectively and safely in enclosed spaces.