Johnson Controls CM8M/CMLM*MP Combustion Air Source From Outdoors, Air Supply Openings and Ducts

368261-UIM-A-0508

An unconfined space is not less than 50 cu.ft (1.42 m3) per 1,000 Btu/ hr (0.2928 kW) input rating for all of the appliances installed in that area.

Rooms communicating directly with the space containing the appli- ances are considered part of the unconfined space, if openings are fur- nished with openings or louvers.

A confined space is an area with less than 50 cu.ft (1.42 m3) per 1,000 Btu/hr (0.2928 kW) input rating for all of the appliances installed in that area. The following must be considered to obtain proper air for combus- tion and ventilation in confined spaces.

Combustion Air Source From Outdoors

The blocking effects of louvers, grilles and screens must be given con- sideration in calculating free area. If the free area of a specific louver or grille is not known, refer to Table 7, to estimate free area.

Table 7: Estimated Free Area

Wood or Metal	Wood 20-25%*
Louvers or Grilles	Metal 60-70% *
Screens+	1/4” (0.635 cm)
	mesh or larger 100%

* Do not use less than 1/4”(0.635 cm) mesh

+Free area of louvers and grille varies widely; the installer should follow louver or grille manufacturer’s instructions.

Dampers, Louvers and Grilles (Canada Only)

1.The free area of a supply air opening shall be calculated by sub- tracting the blockage area of all fixed louvers grilles or screens from the gross area of the opening.

2.Apertures in a fixed louver, a grille, or screen shall have no dimen- sion smaller than 0.25” (0.64 cm).

3.A manually operated damper or manually adjustable louvers are not permitted for use.

4.A automatically operated damper or automatically adjustable lou- vers shall be interlocked so that the main burner cannot operate unless either the damper or the louver is in the fully open position.

When a Category I furnace is removed or replaced, the original venting system may no longer be correctly sized to properly vent the attached appliances.

An improperly sized vent system can cause CARBON MONOXIDE to spill into the living space causing personal injury, and or death.

Table 8: Unconfined Space Minimum Area in Square Inch

BTUH Input Rating				Minimum Free Area in Square Feet
					Required for Each Opening
60,000						60 (387 cm2)
80,000						80 (516 cm2)
100,000						100 (645 cm2)
120,000						120 (742 cm2)
Table 9: Free Area
BTUH Input			Minimum Free Area Required for Each Opening
			Horizontal Duct			Vertical Duct or	Round Duct
Rating						Opening to Outside
			(2,000 BTUH)				(4,000 BTUH)
						(4,000 BTUH)
60,000			30 in2 (193 cm2)			15 in2 (97 cm2)	5” (13 cm)
80,000			40 in2 (258 cm2)			20 in2 (129 cm2)	5” (13 cm)
100,000			50 in2 (322 cm2)			25 in2 (161 cm2)	6” (15 cm)
120,000			60 in2 (387 cm2)			30 in2 (193 cm2)	7” (18 cm)
EXAMPLE:		Determining Free Area.
Appliance			1 Appliance			2 Total Input
100,000	+		30,000 = (130,000 ⎟ 4,000) = 32.5 Sq. In. Vertical
Appliance			1 Appliance			2 Total Input
100,000	+		30,000 = (130,000 ⎟ 2,000) = 65 Sq. In. Horizontal

Gable

Vent

	Ventilated
Optional	Attic
	Top Above
Inlet (a)
	Insulation
Soffit	Outlet
Vent	Air (a)
	Gas
	Water
	Heater
	Ventilated
	Crawl Space

Gas

VentGable

Vent

Ventilated

Attic

Top Above

Insulation

Soffit

Vent

Furnace	Gas
	Water
Inlet	Heater
Air (b)

Gas Vent

Furnace

Gas

Vent

Outlet

Air (b)

Inlet	Inlet	Heater	Furnace
		Gas
		Water
Air (a)	Air (b)

Outlet Air (a)

Inlet

Air (a)

FIGURE 28: Outside and Ambient Combustion Air

Air Supply Openings and Ducts

1.An opening may be used in lieu of a duct to provide to provide the outside air supply to an appliance unless otherwise permitted by the authority having jurisdiction. The opening shall be located within 12” (30.5 cm) horizontally from, the burner level of the appli- ance. Refer to “COMBUSTION AIR SOURCE FROM OUTDOORS and VENT AND SUPPLY AIR SAFETY CHECK” in these instruc- tions for additional information and safety check procedure.

2.The duct shall be either metal, or a material meeting the class 1 requirements of CAN4-S110 Standard for Air Ducts.

3.The duct shall be least the same cross-sectional area as the free area of the air supply inlet opening to which it connects.

4.The duct shall terminate within 12 in (30.5 cm) above, and within 24 in (61 cm) horizontally from, the burner level of the appliance having the largest input.

5.A square or rectangular shaped duct shall only be used when the required free area of the supply opening is 9 in2 (58.06 cm2) or larger. When a square or rectangular duct is used, its small dimen- sionshall not be less than 3 in (7.6 cm).

6.An air inlet supply from outdoors shall be equipped with a means to prevent the direct entry of rain and wind. Such means shall not reduce the required free area of the air supply opening.

7.An air supply inlet opening from the outdoors shall be located not less than 12” (30.5 cm) above the outside grade level.

Combustion Air Source from Outdoors

1.Two permanent openings, one within 12 in (30.5 mm) of the top and one within 12 in (30.5 mm) of bottom of the confined space, Two permanent openings, shall communicate directly or by means of ducts with the outdoors, crawl spaces or attic spaces.

Johnson Controls Unitary Products 19