MGD Gas Furnace
Service Manual
NATURAL GAS
Inlet pressure to the unit should be checked (at the gas valve) with ALL OTHER GAS FIRED
APPLIANCES OPERATING. Inlet pressure to the unit under these conditions MUST be a
minimum of 4.5 in. W.C. If the inlet pressure is less, it may be an indication of undersized piping or
regulator problems.
L. P. GAS
Inlet pressure to the unit should be checked in the same manner as for natural gas, however, with
L.P. Gas, the inlet pressure MUST be a minimum of 11 in. W.C. If this cannot be obtained,
problems are indicated in either the regulator or pipe sizing.
Gas
Pressures
Natural Gas
LP Gas
Minimum
Inlet
4.5”W.C. (1120 Pa)
11”W.C. (2740 Pa)
Recommended
Inlet
7” W.C. (1740 Pa)
11” W.C. (2740 Pa)
Maximum
Inlet
13” W.C. (3230
Pa)
13” W.C. (3230 Pa)
Manifold
Pressure
3.5” W.C. (870 Pa)
10” W.C. (2490
Pa)
CHECKING INPUT (FIRING) RATE
Once it has been determined that the gas supply (inlet) pressure is correct to the unit, it is
necessary to check the input (firing) rate. This can be done in two ways. The preferred method is
to check and adjust (as necessary) the manifold pressure. The second way is to “Clock” the gas
meter (on Natural Gas Models).
CHECKING MANIFOLD PRESSURE
GAS PRESSURE TESTING DEVICES
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