FloAire Non-Welded Grease Duct Systems - Manual (Page 18)

18
Zero Clearances to Combustibles
This duct is to be used in non-combustible surroundings. Where the duct does not require an enclosure, it
must have a minimum clearance to adjacent combustible walls as shown above in Table 5 – CLEARANCES.
In cases where the ducting extends through any story of a building above the location at the connected
appliances, it must be enclosed in the upper stories with walls having a fire resistance rating of not less than
one hour for buildings of two or three stories in height. If the building is four stories or more in height, the
enclosure wall shall have a fire resistance rating of not less than two hours.
METHODS USED TO TEST DUCT AFTER ASSEMBLY
Prior to the concealment of any portion of a grease duct system, a leakage test shall be performed in the
presence of the code official. Duct shall be considered to be concealed where installed in shafts or covered
by coatings or wraps that prevent the ductwork from being visually inspected on all sides. A light test or
approved equivalent test method (smoke test) shall be performed to determine that all joints are liquid tight.
The smoke test is used for longer duct runs while the light test is used for short duct runs, both methods are
approved for use.
Method 1 – Light Test per IMC 506.3.3.1
A light test shall be performed by passing a lamp having a power rating of not less than 100 watts through
the entire section of ductwork to be tested. The lamp shall be open so as to emit light equally in all directions
perpendicular to the duct walls. The test shall be performed for entire duct system, including the hood-to-
duct connection. The ductwork shall be permitted to be tested in sections, provided that every joint is tested.
Method 2 – Smoke Test
After the ductwork has been installed allow the listed sealant to cure for a minimum of 24 hours. Smoke
bombs are lit and placed at the bottom of the duct system, natural upwards drafts will pull the smoke to the
top of the duct system. Various length duct runs may require multiple smoke bombs. Once the smoke has
reached the top of the duct run, cap the duct, making sure it’s secure. Inspect all joints for leakage.
GENERAL DUCT WEIGHT
Two different material gauges are available, 20 gauge is the minimum / 18 gauge is the maximum allowable
material per this listed duct. Both gauges have been tested by ETL and comply with standard UL-1978. 20
gauge is the standard material used in application with 18 inches or more to combustible surfaces. 20 gauge
duct may also be wrapped using a listed duct wrap for zero clearance to combustibles, 18 gauge is required
in some JHA when duct needs to be wrapped using a listed duct wrap for zero clearance to combustibles.
Weight – 20 Gauge Duct
The following formula can be used to approximate the weight of total lengths of duct for 20 GA duct (.0327 x
“L” x “D”). “L” and “D” should be calculated in inches, where L is the length and D is the diameter. Example:
A total length of duct is 25 ft long, 14” diameter (.0327 x (25’ x 12”) x 14” = 137 LBS).
Weight – 18 Gauge Duct
The following formula can be used to approximate the weight of total lengths of duct for 18 GA duct (.0417 x
“L” x “D”). “L” and “D” should be calculated in inches, where L is the length and D is the diameter. Example:
A total length of duct is 25 ft long, 14” diameter (.0417 x (25’ x 12”) x 14” = 175 LBS).