8
ORIFICE INSTALLATION
All burners are equipped with an orifice set at the minimum firing rate (except for OEM
packaged units). Drilling the orifice increases the firing rate. To drill the orifice, first open the
union and then unscrew the orifice from inside the union. Determine the proper orifice size for
the desired firing rate and drill the orifice (see Chart 5). Replace the orifice in the union and
tighten the union so that it is gas tight. Once installed, a higher or lower firing rate can be
achieved by raising or lowering the manifold pressure by +/- 0.3”. Pressure changes can only be
made when the burner is running. The typical working manifold pressure for natural gas is
3.5”
W.C. (2.3” W.C. for LP). The maximum inlet pressure at the gas valve is 11” W.C.; the
minimum is
5” W.C. (for the purpose of input adjustment).
Note: The manifold pressure may vary for OEM packaged units.
Chart 5: Burner Orifice Sizing For Natural Gas And LP*
Orifice Size
(inches)
Drill
Size
Manifold Pressure at 3.5”
W.C. for Nat Gas (BTU)
Manifold Pressure at 2.3”
W.C. for L.P. (BTU)
Approximate
Head Setting
Approximate
Air Setting
5/32
0.156
50,000
50,000
21
0
3/16
0.188
80,000
80,000
18
2
7/32
0.219
90,000
90,000
12
6
15/64
0.234
122,000
122,000
18
14
9/32
0.281
146,000
146,000
14
11
19/64
0.297
160,000
160,000
10
10
27/64
0.422
200,000
200,000
3
15
1/2
no
orifice
250,000
250,000
1
20
* Assumes 0” to –0.02” Draft over fire
INSTALLING THE CHIMNEY LINER, DRAFT DIVERTER AND
VENT PIPE
Some utilities require new chimney liners for all gas installations. Use a corrosion resistant
chimney liner (approved for gas service) of the same size as the vent pipe. Use an CSA or U.L.
listed draft diverter only if you can maintain draft over fire. Otherwise, it is better to use a double
swing draft regulator, listed by CSA or U.L. When the burner is used as a conversion burner,
draft over fire should be maintained as –0.02” W.C. by adjusting the regulator when the burner is
fired. The installer should follow the barometric draft regulator manufacturer’s instructions for
complete details for installations and adjustments. The vent pipe should extend only to (but not
beyond) the inside wall of the chimney.
Summary of Contents for SU-2A
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