Installation instructions
Greentherm T9900 SE/i – 6 720 813 635 (2019/03)
34
GAS LINE SIZING
The gas supply piping for a single heater should be sized for a maximum draw of 199000 BTU/hr for Greentherm T9900 SE/i.
Measure the length of the gas supply line from the building's gas main to the heater and use the chapter 4.8.1 and 4.8.2 or the gas
line manufacturer’s sizing tables to determine the pipe diameter necessary. If there are more gas appliances on the line, size the gas
line according to the total maximum amount of BTU draw input rating of for all appliances combined.
Note:
Undersizing the gas line may result in diminished hot water flow rate and temperature, or improper appliance operation (noise
and combustion instabilities). See chapter 4.13, page 43 for the procedure to measure gas pressure. Proper gas pressure must be
confirmed at time of installation.
4.8.1 Gas Line Sizing Tables for NATURAL GAS
For your convenience, see below an excerpt from gas line sizing tables for a single NG appliance. For details, see the current NFPA
54.
Required input for 160000 / 199000 BTU/hr for the Greentherm T9900 SE/i. The gas supply system must be sized for the
combined total maximum BTU/hr load requirements of all gas appliances running simultaneously.
The tables below show the maximum capacity of the gas supply pipe in cubic feet per hour. Please contact your local gas supplier for
the energy content of the gas to determine the BTU/hr capacity. Use 1,000 BTU/cubic foot for rough estimations.
Table 11 Maximum pipe capacity in cubic feet of Natural Gas per hour for gas pressures of <2.0 psig (55" WC or 138 mbar) and a
pressure drop of 0.5" W.C. (1.25 mbar) based on 0.60 specific gravity gas).
Table 12 Maximum pipe capacity in cubic feet of Natural Gas per hour for gas pressures of <2.0 psig (55" WC or 138 mbar) and a
pressure drop of 3.0” W.C. (7.5 mbar) based on 0.60 specific gravity gas.
Table 13 Maximum pipe capacity in cubic feet of Natural Gas per hour for gas pressures of <2.0 psig (55" WC or 138 mbar) and a
pressure drop of 0.5" W.C. (1.25 mbar) based on 0.60 specific gravity gas).
* EHD = Equivalent Hydraulic Diameter. The greater the value of EHD, the greater the gas capacity of the tubing.
Nominal
Iron Pipe
Size, inches
Internal
Diameter
inches
Length of Black Iron Pipe (Schedule 40 Metallic Pipe), Feet
10
20
30
40
50
60
70
80
90
100
¾
0.824
360
247
199
170
151
137
126
117
110
104
1
1.049
678
466
374
320
284
257
237
220
207
195
Initial Supply Pressure of 8.0" w.c. or Greater
Nominal
Iron Pipe
Size, inches
Internal
Diameter
inches
Length of Black Iron Pipe (Schedule 40 Metallic Pipe), Feet
10
20
30
40
50
60
70
80
90
100
½
0.622
454
312
250
214
190
172
158
147
138
131
¾
0.824
949
652
524
448
397
360
331
308
289
273
1
1.049
1790
1230
986
844
748
678
624
580
544
514
Length of Corrugated Stainless Steel Tubing (CSST), Feet
EHD*
10
20
30
40
50
60
70
80
90
100
30
330
231
188
162
144
131
121
113
107
101
31
383
269
218
188
168
153
141
132
125
118
37
639
456
374
325
292
267
248
232
219
208
