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

The minimum free air requirement for horizontal installations is critical to ensure proper ventilation and to prevent the accumulation of harmful gases. The correct minimum free air requirement is 1 cubic inch per 2000 BTUs of the appliance being served. This ratio helps in maintaining adequate air flow, allowing for efficient combustion and reducing the risk of backdrafts or other ventilation issues.

By adhering to this standard, plumbing systems can ensure that there is sufficient air available to support the appliances’ operation, optimizing performance and compliance with safety regulations. The other choices present ratios that provide insufficient ventilation for most systems, which could lead to unsafe conditions and decreased appliance efficiency.