The standard method for determining the required volume for combustion air from the indoors is ______ cubic feet per 1,000 Btu/h.

The standard method for determining the required volume for combustion air from the indoors is ______ cubic feet per 1,000 Btu/h.

• A. 45
• B. 50
• C. 35
• D. 25

Answer: (B)

The standard method for indoor combustion air uses 50 cubic feet per 1,000 Btu/h of the total input rating of all indoor combustion appliances in the space. This multiplier ensures there’s enough air for proper combustion and safe venting. To apply it, add up the input ratings of every appliance drawing air from indoors, then multiply that total by 50/1,000 to get the minimum room volume in cubic feet. For example, if the combined input is 40,000 Btu/h, the required space would be 40 × 50 / 1,000 = 2,000 ft³. The other values aren’t the standard multiplier for this method; using them would under- or over-size the space and could compromise combustion safety.

The standard method for indoor combustion air uses 50 cubic feet per 1,000 Btu/h of the total input rating of all indoor combustion appliances in the space. This multiplier ensures there’s enough air for proper combustion and safe venting.

To apply it, add up the input ratings of every appliance drawing air from indoors, then multiply that total by 50/1,000 to get the minimum room volume in cubic feet. For example, if the combined input is 40,000 Btu/h, the required space would be 40 × 50 / 1,000 = 2,000 ft³.

The other values aren’t the standard multiplier for this method; using them would under- or over-size the space and could compromise combustion safety.