Gas Fitter Practice Test

What size opening is required in a furnace room door for combustion air if the enclosure is 10ft x 20ft x 7ft?

1. 0 square inches

2. 9 square inches

3. 18 square inches

4. 125 square inches

The correct answer is: 125 square inches

To determine the appropriate size opening for combustion air in a furnace room, it is essential to consider the volume of the enclosure and the requirements set forth by applicable codes and standards for combustion air supply. In this case, the furnace room measures 10 feet by 20 feet with a height of 7 feet, which calculates to a volume of 1400 cubic feet. Typically, the rules governing combustion air states that an opening should provide sufficient air for proper combustion, which can vary depending on the type of appliance (direct vent, natural draft, etc.) and the presence of other appliances or environmental conditions. For non-direct vent appliances in large enclosed spaces, the required combustion air may range based on the BTU (British Thermal Unit) input of the equipment. For general guidelines, the common formula is to provide a minimum of 1 square inch of opening per 1,000 BTU of input for appliances located in a confined space. For larger spaces or where multiple appliances are present, additional considerations apply to ensure adequate airflow, which is where the larger opening of 125 square inches would come into play. The option of 125 square inches is thus a suitable choice, prioritizing safety and efficient combustion within the furnace room. This opening size helps