Bryant 120 instruction manual Gas Rate cu ft/hr, Furnace Overheating Hazard

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Table 12 – Gas Rate (cu ft/hr)

SECONDS	SIZE OF TEST DIAL			SECONDS	SIZE OF TEST DIAL
FOR 1				FOR 1
REVOLUTION	1 CU FT	2 CU FT	5 CU FT	REVOLUTION	1 CU FT	2 CU FT	5 CU FT
10	360	720	1800	50	72	144	360
11	327	655	1636	51	71	141	355
12	300	600	1500	52	69	138	346
13	277	555	1385	53	68	136	340
14	257	514	1286	54	67	133	333
15	240	480	1200	55	65	131	327
16	225	450	1125	56	64	129	321
17	212	424	1059	57	63	126	316
18	200	400	1000	58	62	124	310
19	189	379	947	59	61	122	305
20	180	360	900	60	60	120	300
21	171	343	857	62	58	116	290
22	164	327	818	64	56	112	281
23	157	313	783	66	54	109	273
24	150	300	750	68	53	106	265
25	144	288	720	70	51	103	257
26	138	277	692	72	50	100	250
27	133	267	667	74	48	97	243
28	129	257	643	76	47	95	237
29	124	248	621	78	46	92	231
30	120	240	600	80	45	90	225
31	116	232	581	82	44	88	220
32	113	225	563	84	43	86	214
33	109	218	545	86	42	84	209
34	106	212	529	88	41	82	205
35	103	206	514	90	40	80	200
36	100	200	500	92	39	78	196
37	97	195	486	94	38	76	192
38	95	189	474	96	38	75	188
39	92	185	462	98	37	74	184
40	90	180	450	100	36	72	180
41	88	176	439	102	35	71	178
42	86	172	429	104	35	69	173
43	84	167	419	106	34	68	170
44	82	164	409	108	33	67	167
45	80	160	400	110	33	65	164
46	78	157	391	112	32	64	161
47	76	153	383	116	31	62	155
48	75	150	375	120	30	60	150
49	73	147	367

c. Adjust air temperature rise by adjusting blower speed. Increase blower speed to reduce temperature rise. Decrease blower speed to increase temperature rise. For low heat, speed selection can be low (factory setting), med-low, or med (5-speed blowers only).

d.Remove thermostat jumpers and release Blower Access Door Switch.

e.To change motor speed selection for low heat, remove blower motor lead from control LO-HEAT terminal. (See Fig. 34.) Select desired blower motor speed lead from 1 of the other terminals and relocate it to the LO-HEAT terminal. (See Table 13 for lead color identification). Reconnect original lead to SPARE terminal.

f.Repeat steps a through e.

!CAUTION

FURNACE OVERHEATING HAZARD

Failure to follow this caution may result in reduced furnace life.

Recheck temperature rise. It must be within limits specified on the rating plate. Recommended operation is at the midpoint of rise range or slightly above.

g.When correct low heat input rate and temperature rise is achieved, proceed to Step 6.

6.Adjust Manifold Pressure to Obtain High Heat Rate

a. Remove high fire regulator adjustment cap from gas valve pressure regulator.

b.Manually close blower access door switch.

c.Jumper R, W/W1 and W2 thermostat connections on control to run furnace in high heat. (See Fig. 34.)

d.d. Turn high-heat adjusting screw (3/16 in. or smaller flat tipped screwdriver) counterclockwise (out) to decrease input rate or clockwise (in) to increase rate.

e.Re-install high-fire adjustment caps.

f.Leave manifold or similar device connected and proceed to Step 7.

NOTE: DO NOT set high-heat manifold pressure less than 3.2-in. wc or more than 3.8-in. wc for natural gas. If manifold pressure is outside this range, change main burner orifices.

7.Verify natural gas high heat input rate by clocking meter. NOTE: Gas valve regulator adjustment caps must be in place for proper input to be clocked.

a.Turn off all other gas appliances and pilots served by the meter.

b.Run for 3 minutes in high-heat operation.

c.Measure time (in sec) for gas meter to complete 1 revolution and note reading.

d.Refer to Table 12 for cubic ft of gas per hr.

e.Multiply gas rate cu ft/hr by heating value (Btuh/cu ft) to obtain input.

NOTE: Using the 2 cu. ft or 5 cu. ft gas meter dial provides greater accuracy in verifying gas input rate.

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