Johnson Controls TM9X*MP installation manual Combustion Air Source From Outdoors, Free Area

697936-UIM-B-01211

This type of installation requires that the supply air to the appliance(s) be of a sufficient amount to support all of the appliance(s) in the area. Operation of a mechanical exhaust, such as an exhaust fan, kitchen ventilation system, clothes dryer or fireplace may create conditions requiring special attention to avoid unsatisfactory operation of gas appliances. A venting problem or a lack of supply air will result in a hazardous condition, which can cause the appliance to soot and gen- erate dangerous levels of CARBON MONOXIDE, which can lead to serious injury, property damage and / or death.

An unconfined space is not less than 50 cu.ft (1.42 m3) per 1,000 BTU/hr (0.293 kW/h) 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 doors 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 (0.293 kW/h) input rating for all of the appliances installed in that area. The following must be considered to obtain proper air for combustion 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 11, to estimate free area.

Table 11: Estimated Free Area
Wood or Metal	Wood 20-25%*
Louvers or Grilles	Metal 60-70% *
Screens+	1/4” (6.4 mm)
	mesh or larger 100%

* Do not use less than 1/4” (6.4 mm) 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 1/4” (6.4 mm).

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 vent- ing 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 12: Unconfined Space Minimum Area

BTUH Input Rating				Minimum Free Area Required for Each Opening
40,000					40 in2 (258 cm2)
60,000					60 in2 (387 cm2)
80,000					80 in2 (516 cm2)
100,000					100 in2 (645 cm2)
120,000					120 in2 (742 cm2)
Table 13: Free Area
			Minimum Free Area Required for Each Opening
BTUH Input
			Horizontal Duct		Vertical Duct or	Round Duct
Rating					Opening to Outside
			(2,000 BTUH)			(4,000 BTUH)
					(4,000 BTUH)
40,000			20 in2 (129 cm2)		10in2 (64 cm2)	4” (10 cm)
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

26 Johnson Controls Unitary Products