Lennox International Inc Merit Series Gas Furnace installation instructions

16 − Vent connectors serving Category I appliances shall	two consecutive table size diameters over the size of
not be connected to any portion of mechanical draft	the draft hood outlet or flue collar outlet.
systems operating under positive pressure such as	20 − Do not install a manual damper, barometric draft regu-
Category III or IV venting systems.	lator or flue restrictor between the furnace and the
17 − If vent connectors are combined prior to entering the	chimney.
common vent, the maximum common vent capacity	21 − When connecting this appliance to an existing dedi-
listed in the common venting tables must be reduced by	cated or common venting system, you must inspect the
10%, the equivalent of one 90° elbow (0.90 x maximum	venting system’s general condition and look for signs
common vent capacity).	of corrosion. The existing vent pipe size must conform
18 − The common vent diameter must always be at least as	to these instructions and the provided venting tables. If
large as the largest vent connector diameter.	the existing venting system does not meet these re-
19 − In no case, shall the vent connector be sized more than	quirements, it must be resized.

TABLE 3

Capacity of Type B Double−Wall Vents with Type B Double−Wall Connectors

Serving a Single Category I Appliance

					Vent and Connector Diameter − D (inches)
Height	Lateral
			3 Inch			4 Inch			5 Inch			6 Inch
H	L
					Appliance Input Rating in Thousands of Btu Per Hour
(feet)	(feet)
		MIN		MAX	MIN		MAX	MIN		MAX	MIN		MAX
	0	0		78	0		152	0		251	0		375
	2	13		51	18		97	27		157	32		232
6
	4	21		49	30		94	39		153	50		227
	6	25		46	36		91	47		149	59		223
	0	0		84	0		165	0		276	0		415
	2	12		57	16		109	25		178	28		263
8
	5	23		53	32		103	42		171	53		255
	8	28		49	39		98	51		164	64		247
	0	0		88	0		175	0		295	0		447
	2	12		61	17		118	23		194	26		289
10
	5	23		57	32		113	41		187	52		280
	10	30		51	41		104	54		176	67		267
	0	0		94	0		191	0		327	0		502
	2	11		69	15		136	20		226	22		339
15	5	22		65	30		130	39		219	49		330
	10	29		59	40		121	51		206	64		315
	15	35		53	48		112	61		195	76		301
	0	0		97	0		202	0		349	0		540
	2	10		75	14		149	18		250	20		377
	5	21		71	29		143	38		242	47		367
20
	10	28		64	38		133	50		229	62		351
	15	34		58	46		124	59		217	73		337
	20	48		52	55		116	69		206	84		322
	0	0		100	0		213	0		374	0		587
	2	9		81	13		166	14		283	18		432
	5	21		77	28		160	36		275	45		421
30	10	27		70	37		150	48		262	59		405
	15	33		64	44		141	57		249	70		389
	20	56		58	53		132	66		237	80		374
	30	NA		NA	73		113	88		214	104		346

NOTE − Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other vent configurations, the vent system is assumed to have two 90° elbows. For each additional 90° elbow or equivalent (for example two 45° elbows equal one 90° elbow) beyond two, the maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maxi- mum listed capacity).

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