York GF9S*DH Ambient Combustion Air Supply, Combustion Air Source From Outdoors, Btuh, Example

268890-UIM-B-0607

The combustion air intake pipe should be located either through the wall (horizontal or side vent) or through the roof (vertical vent). Care should be taken to locate side vented systems where trees or shrubs will not block or restrict supply air from entering the terminal.

Also, the terminal assembly should be located as far as possible from a swimming pool or a location where swimming pool chemicals might be stored. Be sure the terminal assembly follows the outdoor clearances listed in Section #1 “COMBUSTION AIR QUALITY (LIST OF CONTAM- INANTS).”

Fresh air pipe can either be routed through the furnace or routed out- side the furnace.

Ambient Combustion Air Supply

This type installation will draw the air required for combustion from within the space surrounding the appliance and from areas or rooms adjacent to the space surrounding the appliance. This may be from within the space in a non-confined location or it may be brought into the furnace area from outdoors through permanent openings or ducts. It is not piped directly into the burner box. A single, properly sized pipe from the furnace vent connector to the outdoors must be provided. For down- flow models combustion air is brought into the furnace through the unit top panel opening. Do not install a pipe into the combustion air pipe at the top of the furnace. Refer to Figures 19 & 26.

This type of installation requires that the supply air to the appli- ance(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 cre- ate 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 appli- ance to soot and generate dangerous levels of CARBON MONOX- IDE, 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. (0.2928 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 not furnished with doors.

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.

VENT PIPE PASSES

COMBUSTION THROUGH TOP PANEL

AIRFLOW

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 12, to estimate free area.

TABLE 12: 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 or louvers and grilles varies widely; the installer should follow lou- ver or grilles

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 grilles, or screen shall have no dimension 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.

TABLE 13: Free Area - Outdoor Air

		Minimum Free Area Required for Each Opening
BTUH Input
		Horizontal Duct	Vertical Duct or	Round Duct
Rating			Opening to Outside	(4,000
		(2,000 BTUH)
			(4,000 BTUH)	BTUH)
40,000		20 sq. in. (129 cm2)	10 sq. in. (65 cm2)	4” (10 cm)
60,000		30 sq. in. (194 cm2)	15 sq. in. (97 cm2)	5” (13 cm)
80,000		40 sq. in. (258 cm2)	20 sq. in. (129 cm2)	5” (13 cm)
100,000		50 sq. in. (323 cm2)	25 sq. in. (161 cm2)	6” (15 cm)
120,000		60 sq. in. (387 cm2)	30 sq. in. (194 cm2)	7” (18 cm)
EXAMPLE:		Determining Free Area.
Appliance		1Appliance	2Total Input
100,000	+	30,000 = (130,000 ⎟ 4,000) = 32.5 Sq. In. Vertical
Appliance		1Appliance	2Total Input
100,000	+	30,000 = (130,000 ⎟ 2,000) = 65 Sq. In. Horizontal

TABLE 14: Unconfined Space Minimum Area in Square Inches

BTUH Input Rating	Minimum Free Area Required for Each Opening
40,000	40 (258 cm2)
60,000	60 (387 cm2)
80,000	80 (516 cm2)
100,000	100 (645 cm2)
120,000	120 (774 cm2)

COMBUSTION AIRFLOW 3-WAY TRANSITION

FIGURE 26: Combustion Airflow Path Through The Furnace Casing to the Burner Box

20 Unitary Products Group