Generac Whole House Generator Clearance

Posted on  by admin
I am currently preparing a quote for a customer to provide and install a standby generator system. I have discovered that in most cases, a generator set placed outside has to maintain a minimum clearance of five feet from the building, if it is constructed of combustible materials.
This particular customer has a 4½ foot swath of space between the side of his garage and a brick-paver walkway. His outside condenser unit is located within this space, and he would like the new generator to be similarly located there.
Here is the section of the NFPA requiring the 5 foot clearance:
NFPA 37, Section 4.1.4, Engines Located Outdoors. Engines, and
their weatherproof housings if provided, that are installed outdoors
shall be located at least 5 ft. from openings in walls and at least 5
ft. from structures having combustible walls. A minimum separation
shall not be required where the following conditions exist:
1. The adjacent wall of the structure has a fire resistance rating
of at least 1 hour.
2. The weatherproof enclosure is constructed of noncombustible
materials and it has been demonstrated that a fire within
the enclosure will not ignite combustible materials outside the
Based on this standard, many manufacturers require that the 5 foot clearance space be maintained on the installation of their units.
Generac, however, allows for an 18" clearance. Here is the text from their installation manual for a residential 14 kW unit:
Annex A — Explanatory Material
A4.1.4 (2) Means of demonstrating compliance are by means of full scale fire test or by calculation procedures.
Because of the limited spaces that are frequently available for installation, it has become apparent that exception (2) would be beneficial for many residential and commercial installations. With that in mind, the manufacturer contracted with an independent testing laboratory to run full scale fire tests to assure that the enclosure will not ignite combustible materials outside the enclosure.
The criteria was to determine the worst case fire scenario within the generator and to determine the ignitability of items outside the engine enclosure at various distances. The enclosure is constructed of non-combustible materials and the results and conclusions from the independent testing lab indicated that any fire within the generator enclosure would not pose any ignition risk to nearby combustibles or structures, with or without fire service personnel response.
Based on this testing and the requirements of NFPA 37, Sec 4.1.4, the guidelines for installation of the generators listed above are changed to 18 inches (457mm) from the back side of the generator to a stationary wall or building.
So it would seem that I can install the unit in that 4½ foot swath of available space if I specify and use a Generac unit.
The question I have is have any of you had to deal with this issue, and are there any other manufacturers that have tested their units to deal with the requirements of NFPA 37 4.1.4?
Edit to add: Here is a link of a formal interpretation of NFPA 37, 4.1.4