Checking the firing rate of a furnace is a very important element of
the installation procedure. Over-firing can cause premature heat exchanger failure.
This is done by measuring the time it takes to consume 1 cubic foot of gas.
When performing this procedure it is important to activate the furnace for about
10-15 minutes, and all the other gas appliances are turned off. Adjust inlet
gas pressure to between 5 and 7 inches water column then time the meter for 2
revolutions and then divide by 2 to get the time for one revolution. Need to
check meter size (1 CuFt or 10 CuFt).
The following table shows approximate gas consumption (measured in cubic feet per
hour), and the gas input (measured in Btu/Hr), based on Natural gas whose caloric
value ranges from 900 to 1050 Btu/cu. ft. We are assuming 1000 Btu/cu. ft.
Gas Input (Btu/Hr) =
(Caloric Value of Gas x 3600) / Meter Time (seconds)This chart assumes a 1 CuFt meter size
Seconds
per cubic
feet |
Consumption
cubic feet
per hour |
Gas
input
btu/hr
@ 1000 btu/cu ft |
20 |
180 |
180,000 |
22 |
164 |
164,000 |
24 |
150 |
150,000 |
26 |
138 |
138,000 |
28 |
129 |
129,000 |
30 |
120 |
120,000 |
32 |
113 |
113,000 |
34 |
106 |
106,000 |
36 |
100 |
100,000 |
38 |
95 |
95,000 |
40 |
90 |
90,000 |
42 |
86 |
86,000 |
44 |
82 |
82,000 |
46 |
78 |
78,000 |
48 |
75 |
75,000 |
50 |
72 |
72,000 |
52 |
69 |
69,000 |
54 |
67 |
67,000 |
56 |
64 |
64,000 |
58 |
62 |
62,000 |
60 |
60 |
60,000 |
62 |
58 |
58,000 |
64 |
56 |
56,000 |
66 |
54 |
54,000 |
68 |
53 |
53,000 |
70 |
51 |
51,000 |
72 |
50 |
50,000 |
74 |
48 |
48,000 |
76 |
47 |
47,000 |
78 |
46 |
46,000 |
80 |
45 |
45,000 |
82 |
44 |
44,000 |
84 |
43 |
43,000 |
86 |
42 |
42,000 |
88 |
41 |
41,000 |
90 |
40 |
40,000 |
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