MGD Gas Furnace
Service Manual
1.
Connect a U-tube manometer or Magnehelic gauge (0-12 in. W.C. range) to the pressure tap
on the OUTLET side of the gas valve.
2. Turn gas ON and fire unit.
3. Manifold pressure should be set to 3.5 in. W.C. for Natural Gas, and to 10 in. W.C. for L.P.
Gas.
4. This valve
is not
field adjustable.
5. For units above 2,000 Ft., insure that orifice size has been changed (per National Fuel Gas
Code
-
Appendix “F”) if gas supply has not already been de-rated for altitude by the gas
supplier.
WARNING
Fire or explosion hazard.
Turn OFF gas at shut off
before connecting U-tube Manometer or Magnehelic.
Failure to turn OFF gas at shut
OFF
before connecting Manometer or Magnehelic
can result in personal injury and/or death.
“CLOCKING” GAS METER (NATURAL GAS)
1. Check with gas supplier to obtain ACTUAL BTU content of gas.
2. Turn OFF gas supply to ALL other gas appliances.
3. Time how many seconds it takes the smallest (normally 1 cfh) dial on the gas meter to make
one complete revolution.
EXAMPLE
Natural Gas
No. of Seconds
Time Per Cubic
BTU's Per
BTU Content
Per Hour
Foot In Seconds
Hour
1000 3,600 48 75,000
1,000 * 3,600 / 48 = 75,000 BTUH
4. Calculate input rate by using ACTUAL BTU content of gas in formula shown in example.
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