Lennox International Inc Lennox Merit Series Gas Furnace Upflow/Horizontal Air Discharge, ML193UH

Vent Piping Guidelines

The ML193UH 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 out­ doors. In Direct Vent installations, combustion air is taken from outdoors and flue gases are discharged outdoors.

Intake and exhaust pipe sizing -- Size pipe according to tables 4 and 5. Count all elbows inside and outside the home. Table 4 lists the minimum vent pipe lengths per­ mitted. Table 5 lists the maximum pipe lengths permitted.

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.

In some applications which permit the use of several differ­ ent sizes of vent pipe, a combination vent pipe may be used. Contact Lennox' Application Department for assis­ tance in sizing vent pipe in these applications.

NOTE - The exhaust collar on all models is sized to accom­ modate 2” Schedule 40 vent pipe. In horizontal applica­ tions, any transition to exhaust pipe larger than 2” must be made in vertical runs of the pipe. Therefore a 2” elbow must be added before the pipe is transitioned to any size larger than 2”. This elbow must be added to the elbow count used to determine acceptable vent lengths. Contact the Applica­ tion Department for more information concerning sizing of vent systems which include multiple pipe sizes.

Exhaust Pipe

Use the following steps to correctly size vent pipe diameter.

Piping Size Process

What is the

furnace capacity?

1045, 070, 090,

110 or 135?

Which style termination

2being used?

Standard or concentric?

See table 3.

Which needs

3most elbows?

Intake or exhaust?

How many elbows?

4Count all elbows inside and outside house.

Desired pipe size?

52”, 2-1/2”, 3”

Horizontal Gas Furnace

Exhaust Pipe

12” Min .

12” max

Of straight pipe

What is the altitude of

6the furnace installation?

Use table 5 or 6 to find max intake or exhaust pipe

7length. Includes all vent pipe and elbows inside and outside the house.

NOTE - All horizontal runs of exhaust pipe must slope back to­ ward unit. A minimum of 1/4” (6mm) drop for each 12” (305mm) of horizontal run is mandatory for drainage.

NOTE - Exhaust pipe MUST be glued to furnace exhaust fittings.

NOTE - Exhaust piping should be checked carefully to make sure there are no sags or low spots.

FIGURE 22

TABLE 4

MINIMUM VENT PIPE LENGTHS

ML193UH	MIN. VENT LENGTH*
MODEL
045, 070, 090, 110	15 ft. or
	5 ft plus 2 elbows or
135	10 ft plus 1 elbow

*Any approved termination may be added to the minimum length listed.

FIGURE 23

IMPORTANT

Do not use screens or perforated metal in exhaust or intake terminations. Doing so will cause freeze-ups and may block the terminations.

Page 17