When all combustion air is supplied by a mechanical system, how much combustion air is needed per 1000 Btu/hr of appliance input?

The correct answer reflects standard guidelines for determining the amount of combustion air required for gas appliances when all combustion air is supplied by a mechanical system. For appliances that utilize mechanical ventilation, the generally accepted requirement is 0.35 cubic feet of combustion air per 1000 Btu/hr of appliance input.

This specific volume ensures that there is sufficient oxygen for efficient combustion and to prevent the formation of dangerous products such as carbon monoxide. By utilizing a mechanical system to supply combustion air, the risk of insufficient air is mitigated, requiring a precise calculation of air needs based on appliance input. This value of 0.35 cubic feet provides a balance between efficiency and safety, which is critical in gas appliance operation.

The other options do not align with this standard requirement for mechanical systems, as they either under- or overestimate the necessary amount of air for optimal combustion in such settings.