Lennox International Inc Gas Units, G61MP Series Units Vent Piping Guidelines

Vent Piping Guidelines

The G61MP can be installed as either a Non−Direct Vent or a Direct Vent gas central furnace.

NOTE − In Non-Direct Vent installations, combustion air is taken from indoors and flue gases are discharged outdoors. In Direct Vent installations, combustion air is taken from out- doors and flue gases are discharged outdoors.

Intake and exhaust pipe sizing in Direct Vent applications and exhaust pipe sizing in Non-Direct Vent applications −− Size pipe according to tables 6 and 7. Table 6 lists the mini- mum equivalent vent pipe lengths permitted. Table 7 lists the maximum equivalent pipe lengths permitted.

Maximum vent length is defined as:

Total length (linear feet) of pipe,

Plus Equivalent length (feet) of fittings,

Plus Equivalent length (feet) of termination.

NOTE − Include ALL pipe and ALL fittings, both in doors and outdoors.

Regardless of the diameter of pipe used, the standard roof and wall terminations described in section Exhaust Piping Terminations should be used. Exhaust vent termination pipe is sized to optimize the velocity of the exhaust gas as it exits the termination. Refer to table 8.

*NOTE − The exhaust pipe should be offset a minimum of 12 inches to avoid the possibility of water droplets being re-

leased from the exhaust termination. The minimum ex- haust vent length is 15 ft. Shorter exhaust vent lengths may result in the discharge of water droplets from the exhaust termination, in spite of the 12−inch vertical offset. See fig- ure 21.

Each 90° elbow (including those provided with the furnace) of any diameter is equivalent to 5 feet (1.52m) of vent pipe of the same diameter. Two 45° elbows are equivalent to one 90° elbow of the same diameter. One 45° elbow is equal to 2.5 feet (.76m) of vent pipe of the same diameter. In some applications which permit the use of several differ- ent sizes of vent pipe, a combination vent pipe may be used. Contact the Application Department for assistance in sizing vent pipe in these applications.

NOTE − The flue collar on all models is sized to accommo- date 2" Schedule 40 flue pipe. When vent pipe which is larger than 2" must be used in an upflow application, a 2" elbow must be applied at the flue collar in order to proper- ly transition to the larger diameter flue pipe. This elbow must be added to the elbow count used to determine ac- ceptable vent lengths. Assign an equivalent feet value to this elbow according to the larger size pipe being used. Contact Lennox’ Application Department for more infor- mation concerning sizing of vent systems which include multiple pipe sizes.

	Exhaust Pipe Offset
	12" Min.
*12" Min.
Upflow and Downflow Application	Upflow and Downflow Application
Rooftop Termination	Side Wall Termination
*12" Min.	*12" Min.

Horizontal Application Rooftop Termination

Horizontal Application Side Wall Termination

*A minimum of 1/4" (6mm) drop for each 12" (305mm) of horizontal run is mandatory for drainage

FIGURE 21

Page 18