Bryant 340MAV instruction manual Combustion-Air and Vent Pipe Diameter, Example

TABLE 6—APPROVED COMBUSTION-AIR AND VENT PIPE, FITTING AND CEMENT MATERIALS

ASTM SPECIFICATION	MATERIAL	PIPE	FITTINGS	SOLVENT CEMENT AND PRIMERS	DESCRIPTION
(MARKED ON MATERIAL)
D1527	ABS	Pipe	—	—	Schedule-40
D1785	PVC	Pipe	—	—	Schedule-40
D2235	For ABS	—	—	Solvent	For ABS
				Cement
D2241	PVC	Pipe	—	—	SDR-21 & SDR-26
D2466	PVC	—	Fittings	—	Schedule-40
D2468	ABS	—	Fittings	—	Schedule-40
D2564	For PVC	—	—	Solvent	For PVC
				Cement
D2661	ABS	Pipe	Fittings	—	DWV at Schedule-40 IPS sizes
D2665	PVC	Pipe	Fittings	—	DWV
F438	CPVC	—	Fittings	—	Schedule-40
F441	CPVC	Pipe	—	—	Schedule-40
F442	CPVC	Pipe	—	—	SDR
F493	For CPVC	—	—	Solvent	For CPVC
				Cement
F628	ABS	Pipe	—	—	Cellular Core DWV at Schedule-40 IPS sizes
F656	For PVC	—	—	Primer	For PVC
F891	PVC	Pipe	—	—	Cellular Core Schedule-40 & DWV

NOTE: The minimum combustion-air and vent pipe length (each) for these furnaces is 5 ft. Short pipe lengths (5-8 ft) may discharge water droplets. These droplets may be undesirable, and a 12-in. minimum offset pipe section is recommended, as shown in Fig. 34, to reduce excessive droplets from exiting vent pipe outlet.

B.Combustion-Air and Vent Pipe Diameter

Determine combustion-air and vent pipe diameter.

1.Using Table 7, individually determine the smallest combustion-air and vent pipe diameters permitted for each pipe. Pick the larger of these 2 pipe diameters and use this diameter for both combustion-air and vent pipes.

NOTE: Select 1 vent pipe connection and		NOTE: Select 1 vent pipe connection and
1 combustion-air pipe connection.		1 combustion-air pipe connection.
AIR
COMBUSTION- FLOW COMBUSTION-
AIR	AIR	VENT
VENT				VENT
	VENT
		COMBUSTION-	COMBUSTION-
		AIR	AIR	AIR
			FLOW
UPFLOW		DOWNFLOW
			COMBUSTION-
COMBUSTION-			AIR
AIR			VENT
VENT

AIR	AIR
FLOW	FLOW

HORIZONTAL-LEFT DISCHARGE HORIZONTAL-RIGHT DISCHARGE

A96187

Fig. 33—Combustion-Air and Vent Pipe Connections

—25—

2.When installing vent systems of short pipe length, use the smallest allowable pipe diameter. Do not use pipe size greater than required or incomplete combustion, flame disturbance, or flame sense lockout may occur.

NOTE: Do not count elbows or pipe sections in terminations or within furnace. See shaded areas in Fig. 36, 37, 38, 39, and 40.

EXAMPLE:

An 036080 size furnace located in Indianapolis, elevation 650 ft above sea level, could be installed in an application requiring 3 elbows and 32 ft of vent pipe, along with 5 elbows and 34 ft of combustion-air pipe. Table 7 indicates this application would allow a 2-in. diameter vent pipe, but require a 2-1/2 in. diameter combustion air pipe (2-in. pipe is good for 35 ft with 3 elbows, but only 30 ft with 5 elbows). Therefore, 2-1/2 in. diameter pipe must be used for both vent and combustion-air pipes since larger required diameter must always be used for both pipes. If same installation were in Albuquerque, elevation 5250 ft above sea level, installation would require 2-1/2 in. vent pipe and combustion-air pipe. At 5001- to 6000-ft elevation, 2-in. pipe is only good for 17 ft with 5 elbows, and 2-1/2 in. pipe is good for 70 ft with 5 elbows.

C. Combustion-Air and Vent Pipe Attachment

NOTE: All pipe joints must be cemented except attachment of combustion-air pipe to inlet housing connection, since it may be necessary to remove pipe for servicing.

1.Attach combustion-air pipe as follows:

a.Determine location of combustion-air intake pipe con- nection to combustion-air intake housing as shown in Fig. 33 for application.

b.Reposition combustion-air intake housing plug fitting in appropriate unused intake housing connection.

c.If required per Table 7, insert perforated disk assembly (factory-supplied in loose parts bag) in intake housing where combustion-air intake pipe will be connected. If half disk set is required, install with shoulder of disk against stop in combustion-air inlet.