The minimum required volume for indoor combustion air is how many ft³/1000 BTU/hr?

The minimum required volume for indoor combustion air is how many ft³/1000 BTU/hr?

• A. 25 ft³/1000 BTU/hr
• B. 75 ft³/1000 BTU/hr
• C. 50 ft³/1000 BTU/hr
• D. 100 ft³/1000 BTU/hr

Answer: (C)

Providing enough combustion air for an appliance in an indoor, enclosed space is essential for safe operation. The standard rule is to allocate 50 cubic feet of air for every 1,000 BTU per hour of the appliance’s input. This minimum helps ensure there’s enough oxygen for complete combustion and reduces the risk of dangerous buildup of carbon monoxide from backdrafting or incomplete burning. For example, a furnace rated at 100,000 BTU/hr would require at least 100 × 50 = 5,000 ft³ of indoor air. If you have multiple appliances, you sum their inputs and multiply by 50 to find the total required indoor air volume. The other numbers are not the minimum: 25 ft³/1000 BTU/hr would be too low, while 75 or 100 ft³/1000 BTU/hr exceed the minimum needed.

Providing enough combustion air for an appliance in an indoor, enclosed space is essential for safe operation. The standard rule is to allocate 50 cubic feet of air for every 1,000 BTU per hour of the appliance’s input. This minimum helps ensure there’s enough oxygen for complete combustion and reduces the risk of dangerous buildup of carbon monoxide from backdrafting or incomplete burning.

For example, a furnace rated at 100,000 BTU/hr would require at least 100 × 50 = 5,000 ft³ of indoor air. If you have multiple appliances, you sum their inputs and multiply by 50 to find the total required indoor air volume. The other numbers are not the minimum: 25 ft³/1000 BTU/hr would be too low, while 75 or 100 ft³/1000 BTU/hr exceed the minimum needed.