When terminating a vertical duct for combustion air in a confined space, how many square inches must be allocated for every 4,000 Btu/h?

For every 4,000 Btu/h of input, there should be 1 square inch allocated for combustion air in a confined space. This guideline is crucial for ensuring that appliances have an adequate supply of air for proper combustion, which in turn helps to maintain efficiency and safety. The requirements for combustion air are based on the amount of energy being consumed by the appliance, and having the correct number of square inches for air intake is vital to prevent issues such as backdrafting or improper combustion, which can lead to hazardous situations.

In calculations for combustion air allocation, the 1 square inch per 4,000 Btu/h standard allows for a systematic approach to ventilating appliances, ensuring the safe operation of gas-fired equipment. This rule is often cited in building codes and standards to ensure compliance and safety in HVAC and gas installation practices.