CSLB Class B General Contractor's License Practice Exam

What must be provided from a source outside the structure when installing a heating furnace in a closet?

1. Venting inside

2. Combustion air outside

3. Combustion air inside

4. All of the above

The correct answer is: Combustion air outside

When installing a heating furnace in a closet, it is essential to provide combustion air from an outside source. This is because furnaces require air to support the combustion process, and sourcing that air from outside ensures that the furnace can operate efficiently and safely. Using outside combustion air helps to prevent the furnace from depleting the available oxygen in the room where it is installed, which could lead to poor combustion and the production of harmful gases, such as carbon monoxide. Furthermore, outside air is generally cooler and drier, which is beneficial for the combustion efficiency compared to potentially warmer, more humid air from inside the building. Venting inside, while necessary for exhaust, does not address the need for adequate combustion air. Additionally, relying solely on combustion air from within the structure can lead to issues like backdrafting or insufficient airflow for combustion, causing safety concerns and decreased efficiency. Therefore, ensuring that the furnace has combustion air supplied from outside not only meets building safety codes but also promotes optimal operation of the heating system.