The standard calculation for indoor combustion air volume yields how many cubic feet per 1,000 Btu/h?

The standard calculation for indoor combustion air volume yields how many cubic feet per 1,000 Btu/h?

• A. 25
• B. 50
• C. 75
• D. 100

Answer: (B)

The calculation uses a standard indoor combustion air sizing rule: for every 1,000 Btu per hour of appliance input, you need 50 cubic feet of air in the space. So you take the appliance’s input rating in Btu/h, divide by 1,000, and multiply by 50 to get the required room volume in cubic feet. For example, a furnace rated at 40,000 Btu/h would require 40 × 50 = 2,000 ft³ of indoor air. If multiple appliances share the space, sum their Btu/h inputs and apply the same calculation. This rule provides the required air in a typical confined-space scenario unless outdoor openings or mechanical ventilation change the method.

The calculation uses a standard indoor combustion air sizing rule: for every 1,000 Btu per hour of appliance input, you need 50 cubic feet of air in the space. So you take the appliance’s input rating in Btu/h, divide by 1,000, and multiply by 50 to get the required room volume in cubic feet. For example, a furnace rated at 40,000 Btu/h would require 40 × 50 = 2,000 ft³ of indoor air. If multiple appliances share the space, sum their Btu/h inputs and apply the same calculation. This rule provides the required air in a typical confined-space scenario unless outdoor openings or mechanical ventilation change the method.