Comfort-Aire TGRG Series for R-410A - Manual (Page 21)

C. NOx MODELS
When converting units equipped with NOx inserts to LP gas, the stainless steel mesh
inserts in the entrance of the tubular exchangers are not required to meet SCAQMD NOx
emission levels. Carefully remove these inserts before firing this furnace on LP gas. This
furnace is not designed to operate on LP gas with the NOx inserts in place.
Step by step instructions on removing the NOx inserts and retaining rod are included in the
Conversion Kit Installation Instructions.
D. ADJUSTING OR CHECKING FURNACE INPUT
– Natural Gas Line Pressure 5” - 10.5” W.C.
– LP Gas Line Pressure 11” - 13” W.C.
– Natural Gas Manifold Pressure 3.5” W.C
– LP Gas Manifold Pressure - 10” W.C.
Supply and manifold pressure taps are located on the gas valve body 1/8” N.P.T.
Use a properly calibrated manometer gauge for accurate gas pressure readings.
Only small variations in the gas flow should be made by means of the pressure regulator
adjustment. Furnaces functioning on LP gas must be set by means of the tank or branch
supply regulators. The furnace manifold pressure should be set at 10” W.C. at the gas con-
trol valve.
To adjust the pressure regulator, remove the regulator cap and turn the adjustment screw
clockwise to increase pressure or counterclockwise to decrease pressure. Then replace
the regulator cap securely.
Any necessary major changes in the gas flow rate should be made by changing the size of
the burner orifices. To change orifice spuds, shut off the manual main gas valve and
remove the gas manifold.
For elevations up to 2,000 feet, rating plate input ratings apply. For high altitudes (elevations
over 2,000 ft.), see conversion kit index 92-21519-XX for derating and orifice spud sizes.
Check of input is important to prevent over-firing of the furnace beyond its design-
rated input. NEVER SET INPUT ABOVE THAT SHOWN ON THE RATING PLATE. Use
the following table or formula to determine input rate.
Heating Value of Gas
(BTU/Cu. Ft.) x 3600
Cu. Ft. Per Hr. Required =
Time in Seconds
(for 1 Cu. Ft.) of Gas
Maximum capacity of pipe in thousands of BTU per hour of undiluted liquefied petroleum
gases (at 11 inches water column inlet pressure).
(Based on a Pressure Drop of 0.5 Inch Water Column)
TABLE 2
LP GAS PIPE CAPACITY TABLE (CU. FT./HR.)
Nominal
Iron Pipe
Size, Inches
10 20 30 40 50 60 70 80 90 100 125 150
275 189 152 129 114 103 96 89 83 78 69 63
567 393 315 267 237 217 196 182 173 162 146 132
1,071 732 590 504 448 409 378 346 322 307 275 252
2,205 1,496 1,212 1,039 913 834 771 724 677 630 567 511
3,307 2,299 1,858 1,559 1,417 1,275 1,181 1,086 1,023 976 866 787
6,221 4,331 3,465 2,992 2,646 2,394 2,205 2,047 1,921 1,811 1,606 1,496
1/2
3/4
1
1-1/4
1-1/2
2
Length of Pipe, Feet
Example (LP): Input BTU requirement of unit, 150,000
Equivalent length of pipe, 60 ft. = 3/4” IPS required.
21