Designer Guide
15
LOCHINVAR, LLC
300 MADDOX SIMPSON PKWY
LEBANON, TN 37090
www.lochinvar.com
Designer’s Guide / Knight XL Boiler
Chapter 3 – Gas Supply
Lochinvar products are designed with the concept of flame control. We develop combustion
systems that tightly control the flow of air and gas to deliver a clean and efficient flame. In
Chapters 1 and 2, we showed the various methods to deliver an ample quantity of air to the
appliance. In Chapter 3, we discuss delivering a steady and reliable supply of gas to the
appliance.
The key to the gas supply is sizing the gas line properly. The Knight XL will require less than a
half a pound of pressure. The following Sizing Chart is based on less than ½ pound of pressure
or less than 14 inches of pressure. The table is derived from the ANSI Z223.1, the National Fuel
Gas Code.
Simply calculate the total linear feet of straight gas pipe. Figure each elbow as equal to five
straight feet of pipe. Working down the column that matches your pipe length, find the value
GREATER THAN the total Btu/hr input of the boiler or boilers. This will identify the minimum
nominal iron pipe size.
GAS PIPE SIZING CHART
Nominal
Iron
Length of Pipe in Straight Feet
Pipe
Size
10
20
30
40
50
60
70
80
90
100
125
150
175
200
1"
697
477
384
328
292
267
246
256
210
200
179
164
149
138
1 1/4"
1,400
974
789
677
595
543
502
472
441
410
369
333
308
287
1 1/2"
2,150
1,500
1,210
1,020
923
830
769
707
666
636
564
513
472
441
2"
4,100
2,820
2,260
1,950
1,720
1,560
1,440
1,330
1,250
1,180
1,100
974
871
820
2 1/2"
6,460
4,460
3,610
3,100
2,720
2,460
2,310
2,100
2,000
1,900
1,700
1,540
1,400
1,300
3"
11,200
7,900
6,400
5,400
4,870
4,410
4,000
3,800
3,540
3,300
3,000
2,720
2,500
2,340
4"
23,500
16,100
13,100
11,100
10,000
9,000
8,300
7,690
7,380
6,870
6,150
5,640
5,130
4,720
The Knight XL features a Negative-Regulation or Neg-Reg gas combustion system. The gas is
introduced upstream of the combustion blower. As the blower draws air in, the negative pressure
on the inlet of the blower pulls the gas from the gas valve. The gas/air mixture passes through
the blower into the burner. The gas/air mixture filters through the micro-metal burner mesh and is
ignited by the Spark Igniter.
On full fire, a crisp blue flame rises off the surface of the burner.
As demand decreases, the operating control reduces the blower
speed. The flame is reduced and it touches the burner surface.
The micro-metal fiber burner material is designed to burn infra-red
safely without being damaged by direct contact with the flame.
Even at this reduced Btu/hr input, the gas/air mixture is balanced
to provide clean, efficient combustion.
Gas