In an existing system, the vertical clearance between a high volume low speed (HVLS) fan and a sprinkler shall be

According to NFPA 13, Standard for the Installation of Sprinkler Systems, the minimum required vertical clearance between a sprinkler deflector and the plane of the blades of a High Volume Low Speed (HVLS) fan is 36 in. (900 mm). This requirement is based on extensive full-scale fire testing which demonstrated that a smaller clearance could allow the large fan blades to severely disrupt the sprinkler's water distribution pattern, compromising its ability to control a fire. The standard does not specify a different clearance for existing systems; therefore, this minimum safety dimension applies.

A. 12 in. (300 mm): This distance is significantly less than the code-mandated minimum and would present a severe obstruction to the sprinkler discharge pattern.

B. 24 in. (600 mm): This clearance is insufficient and does not meet the 36 in. (900 mm) minimum requirement established in NFPA 13 based on fire test data.

D. 48 in. (1200 mm): While a clearance of 48 in. would be compliant as it exceeds the minimum, it is not the specified minimum requirement.

1. NFPA 13, Standard for the Installation of Sprinkler Systems, 2022 Edition.

Section 13.3.4.2: "The vertical clearance from the sprinkler deflector to the plane of the fan blades shall be a minimum of 36 in. (900 mm)."

Annex A.13.3.4.2: Explains that the 36 in. (900 mm) clearance was determined from full-scale fire testing where lesser clearances resulted in the fan blades blocking sprinkler discharge.

2. Fire Protection Research Foundation Report, "Sprinkler Protection for High-Volume Low-Speed (HVLS) Fans" (December 2009).

Section 5.0, Conclusions, Recommendation 1, page 31: "A minimum 3 ft. (0.9 m) vertical clearance should be maintained between the sprinkler deflector and the fan blades." This foundational research directly informed the inclusion of the 36 in. requirement in NFPA 13.