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

TABLE 7

Maximum Allowable Exhaust Vent Pipe Length (in ft.) Without Insulation In Unconditioned Space For

Winter Design Temperatures Single - Stage High Efficiency Furnace

Winter Design	Vent Pipe			Unit Input Size
Temperatures1 °F (°C)	Diameter	045	070	090	110	135
		PVC	PVC	PVC	PVC	PVC
32 to 21	2 in.	26	44	44	24	N/A
(0 to -6)	2-1/2 in.	18	32	50	58	N/A
	3 in.	14	26	38	55	60
	2 in	16	28	40	24	N/A
20 to 1
	2-1/2 in.	12	20	30	44	N/A
(-7 to -17)
	3 in.	9	16	26	32	40
	2 in.	10	20	30	24	N/A
0 to -20
	2-1/2 in.	8	14	20	32	N/A
(-18 to -29)
	3 in.	4	10	16	26	30

1Refer to 99% Minimum Design Temperature table provided in the current edition of the ASHRAE Fundamentals Handbook.

NOTE - Maximum unisulated vent lengths listed may include the termination(vent pipe exterior to the structure) and cannot exceed 5 linear feet or the maximum allowable intake or exhaust vent length listed in table 5 or 6 which ever is less.

NOTE - If insulation is required in an unconditioned space, it must be located on the pipe closest to the furnace. See figure32.

	Conditioned
	Space
		Exhaust
	Pipe Insulation	Pipe
Conditioned		Intake
	Unconditioned	Pipe
Space
	Space

FIGURE 32

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