Indiana Administrative Code › Title 675 - FIRE PREVENTION AND BUILDING SAFETY COMMISSION › Article 15 - INDUSTRIALIZED BUILDING SYSTEMS › Rule 2 - Indiana Mobile Structures Code › Section 2-87 - Circulating air system

Current through July 10, 2024
Authority: IC 22-13-2-13
Affected: IC 22-12; IC 22-13; IC 22-14; IC 22-15
Sec. 87.
(a) Supply
				systems shall be as follows:
(1) Supply ducts
				and any dampers contained therein shall be made from galvanized steel,
				tinplated steel, or aluminum, or shall be listed Class 0, Class 1, Class 2 air
				ducts. Class 2 air ducts shall be located at least three feet (3') from the
				furnace bonnet or plenum. A duct system integral with the structure shall be of
				durable construction that can be demonstrated to be equally resistant to fire
				and deterioration. Ducts constructed from sheet metal shall be in accordance
				with the following Table No. 4B.
TABLE NO. 4B
Minimum Metal Thickness for Ducts*
Duct Type
Diameter or Width
14 inches or less
over 14 inches
Round
0.013 in.
0.016 in.
Enclosed Rectangular
0.013 in.
0.016 in.
Exposed Rectangular
0.016 in.
0.019 in.
*When "nominal" thickness is specified, 0.003 inch shall be
				  added to these "minimum" metal thicknesses.
(2) Sizing of Ducts. Ducts shall be designed
				so that when a labeled forced-air furnace is installed and operated continually
				at its normal input rating in the mobile structure, with all registers in full
				open position, the static pressure measured in the duct plenum shall not exceed
				that shown in Table No. 4B or exceed that shown on the label of the appliance.
				When an air-cooler coil is installed between the furnace and the duct plenum,
				the total static pressure between the furnace and the coil shall not exceed
				that shown on the label of the furnace. The minimum dimension of any branch
				duct shall be at least one and one-half inches (1 1/2"), and of any main duct,
				two and one-half inches (2 1/2").
(3) Airtightness of Supply Duct Systems. A
				supply duct system shall be considered substantially airtight when the static
				pressure in the duct system, with all registers sealed and with the furnace air
				circulator at high speed, is at least eighty percent (80%) of the static
				pressure measured in the furnace casing, with its outlets sealed and the
				furnace air circulator operating at high speed. For the purpose of this
				subdivision and (b), pressures shall be measured with a water manometer or
				equivalent device calibrated to read in increments not greater than one-tenth
				inch (1/10") water column.
TABLE NO. 5B
Maximum Allowable Static Pressures in
							 Supply Duct Systems
Input to Forced-Air Furnace, Btu/hr
External Static Pressure Inches Water
							 Column Measured at the Furnace Outlet
Temperature of Outlet Air Determined by
							 Function of Limit Control
Above 165°F
165° F or Less
55,000 and under
0.10
0.20
Over 55,000 to 80,000
0.10
0.24
Over 80,000 to 100,000
0.15
0.30
(4)
				Expandable or Multiple Mobile Structure Connections. An expandable or multiple
				structure may have ducts of the heating system installed in the various units.
				The points of connection must be so designed and constructed that when the
				mobile structure is fully expandable or coupled, the resulting duct joint will
				conform to the requirements of this section.
(5) Air supply ducts that are not located
				within the heated side of the mobile structure insulation having an R factor of
				at least four (4) shall be insulated.
(6) Supply ducts within the mobile structure
				but not within insulation described in (a)(5) shall be insulated with rigid
				insulation having a thermal insulation (R) not less than 2.5 or flexible
				insulation having a thermal insulation (R) not less than three (3) with a
				continuous vapor barrier having a perm rating of not more than 1.0.
(7) Supply ducts exposed directly to outside
				air, such as under chassis crossover ducts, shall be insulated with material
				having a thermal insulation (R) of not less than 4.0 with continuous vapor
				barrier having a perm rating of not more than 1.0.
(8) Aluminum foil used as a vapor barrier
				shall be at least two (2) mils in thickness.