The NEC mandates a minimum 3-foot clearance between generators and any combustible materials, such as wood, drywall, or insulation. This distance is critical to reducing the risk of fire caused by heat or electrical faults within the generator housing. Units that do not feature the SwRI logo must be installed 5 ft. Some local codes may require even greater. 5 ft. based on testing done by the Southwest Research. The front and the two ends of the generator require a minimum clearance of 3 feet (36 inches). This perimeter is necessary to allow service technicians to open the enclosure doors, perform routine maintenance, and access internal components for repairs. But for indoor installations, I think this doesn't apply.
This requirement mandates a greater clearance distance from all building openings than the structural clearance for the wall itself. National Fire Protection Association (NFPA) 37 mandates that the generator must be located at least 5 feet from any opening in the structure.
18 in. of clearance from the back of the generator to a stationary wall or building (based on testing done by the Southwest Research Institute or SwRI). 5 ft. of clearance above the generator. 3 ft. of clearance at the front and both ends. This includes trees, shrubs, and bushes.
To meet generator room requirements, consider: Doorway sizing: Doors should be wide enough for generator equipment, tanks, and parts to pass through. The minimum standard is 36 inches. Clearance for maintenance: Ensure that all serviceable parts of the generator have at least 36 inches of clearance in front.
Minimum clearance requirements: NFPA 110 recommends a minimum of three feet at the front and sides of the generator for access, while NFPA 37 calls for five feet for clearance from the opening, combustible walls, and for general access. A thoughtful generator room layout considers the flow of people, equipment, and airflow. Assess the following: