Final Manifold Pressure Settings

Installer’s Guide

▲! CAUTION

Replace and/ or tighten all plugs removed or loosened when adjusting gas pressure. Leak check the fittings before placing the furnace into regular service.

Failure to follow this warning could result in fire, ex- plosion, or property damage.

NOTE:

The manifold pressure must be referenced to the burner box. The burner box pressure tap equalizes the gas valve pressure regulator. Manifold pressure is checked by installing a tee (field supplied) in the tub- ing, between the tee coming from the burner box tube and the gas valve, in addition to the regular gas valve pressure tap on the outlet side of the gas valve. See Figure 51.

▲! CAUTION

Replace manifold pressure tap threaded plug and leak check after checking/ adjusting manifold gas pressure.

Table 11 lists the main burner orifices used with the fur- nace. If a change of orifices is required to correct the furnace input rating refer to Table 14.

TABLE 12

FUEL	PRESSURE

NATURAL GAS	3.5" W.C.

LP GAS	11.0" W.C.

HIGH ALTITUDE DERATE

Input ratings (BTUH) of these furnaces are based on sea level operation and should not be changed at eleva- tions up to 2,000 ft.

If the installation is 2,000 ft. or above, the furnace input rate (BTUH) shall be reduced 4% for each 1,000 ft. above sea level. The furnace input rate shall be checked by clocking the gas flow rate (CFH) and multiplying by the heating value obtained from the local utility sup- plier for the gas being delivered at the installed altitude.

Input rate changes can be made by adjusting the mani- fold pressure (min 3.0 - max 3.7 in. W.C. - Natural Gas) or changing orifices (orifice change may not always be required). If the desired input rate can not be achieved with a change in manifold pressure, then the orifices must be changed. LP installations will require an orifice change.

Installation of this furnace at altitudes above 2,000 ft. (610m) shall be in accordance with local codes, or in the absence of local codes, the National Fuel Gas Code,

TABLE 13

GAS FLOW IN CUBIC FEET PER HOUR

2 CUBIC FOOT DIAL

SEC.	FLOW	SEC.	FLOW	SEC.	FLOW	SEC.	FLOW
8	900	29	248	50	144	82	88
9	800	30	240	51	141	84	86
10	720	31	232	52	138	86	84
11	655	32	225	53	136	88	82
12	600	33	218	54	133	90	80
13	555	34	212	55	131	92	78
14	514	35	206	56	129	94	76
15	480	36	200	57	126	96	75
16	450	37	195	58	124	98	73
17	424	38	189	59	122	100	72
18	400	39	185	60	120	104	69
19	379	40	180	62	116	108	67
20	360	41	176	64	112	112	64
21	343	42	172	66	109	116	62
22	327	43	167	68	106	120	60
23	313	44	164	70	103	124	58
24	300	45	160	72	100	128	56
25	288	46	157	74	97	132	54
26	277	47	153	76	95	136	53
27	267	48	150	78	92	140	51
28	257	49	147	80	90	144	50

32	18-CD22D1-8

Installer’s Guide