For a furnace with a 120,000 BTU/h input rating, what is the required volume for sufficient combustion air in an ordinarily tight construction building?

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To determine the required volume for sufficient combustion air in a building with ordinarily tight construction, it's essential to apply appropriate standards for combustion air calculations. For gas-fired furnaces, a general guideline is to provide 1 cubic foot of air for every 1,000 BTU of input rating.

In this case, the furnace has an input rating of 120,000 BTU/h. By dividing this number by 1,000, we find that we need 120 cubic feet of air for combustion. However, when applied specifically to a typically tight construction building, there are additional considerations which require a volumetric calculation over a larger air volume to ensure adequate air supply for proper combustion without drawing in air from other spaces excessively.

The formula that is commonly used for this calculation in tightly constructed buildings is to consider a minimum of 50 cubic feet of air per 1,000 BTU of furnace input. Applying this calculation:

120,000 BTU/h ÷ 1,000 BTU = 120

Thus, the minimum volume of combustion air needed is:

120 x 50 = 6,000 cubic feet

This is the reason the correct answer is 6,000 ft³, ensuring there is enough air for proper combustion,

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