For horizontal installations, what is the minimum free air requirement?

The correct answer regarding the minimum free air requirement for horizontal installations is 1 cubic inch per 2000 BTU of input. This guideline is important because it ensures that there is sufficient ventilation for combustion appliances, which helps to maintain safe operation and efficiency.

In horizontal installations, proper airflow is critical to prevent combustion problems that could arise from inadequate oxygen supply. If the air intake is too restricted, it could lead to inefficient combustion, the buildup of harmful gases, or even appliance failure.

The specific requirement of 1 cubic inch per 2000 BTU relates to the need for a certain volume of air to be available for every unit of energy input. This guideline is grounded in the understanding of how combustion processes function and the requirements for air to fuel ratios. Ensuring that installations meet this criterion promotes safety and effective performance of the appliances being installed.

Other options, which stipulate higher cubic inches per input energy, would not comply with established regulations and practical applications of plumbing and gas installation codes, as they would provide insufficient air for effective combustion.