Bard WG241D, Installation Instructions Manual

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Manual 2100-376
Page 24
NATURAL GAS INPUT RATE
Natural gas heating value (BTU/cu. ft.) can vary
significantly. Before starting natural gas input check,
obtain gas heating value at your location from local
supplier. You will need a stopwatch to measure actual
gas input.
1. Gas supply pressure must be between 5 and 7 inches
W.C. for natural gas.
2. Turn off all other gas appliances. You may leave
pilots on.
3. Start furnace following "Operating Instructions" on
front door.
4. Let furnace warm up for 6 minutes.
5. Locate gas meter. Determine which dial has the
least cubic feet of gas and how many cubic feet per
revolution it represents. This is usually one-half,
one or two cubic feet per revolution.
6. With stopwatch, measure time it takes to consume
two cubic feet of gas.
• If dial is one-half cubic foot per revolution,
measure time for four revolutions.
• If dial is one cubic foot per revolution, measure
time for two revolutions.
• If dial is two cubic feet per revolution, measure
time for one revolution.
7. Divide this time by two. This gives average time for
one cubic foot of gas to flow through meter.
Example: If it took 58 seconds for two cubic feet to
flow, it would take 29 seconds for one cubic foot to
flow.
8. Calculate gas input using this formula:
Gas Heating Value (BTU/cu. ft.)
x 3,600 sec/hr
Gas input = = BTU/hour
Time (Seconds for one
cubic foot of gas)
Example:
Assume it took 29 seconds for one cubic foot of gas
to flow and heating value of 1,000 BTU/cu. ft.
1,000 x 3,600
Gas input = =
124,138
BTU
29
If you left no other pilots on, this is the furnace gas
input.
9. If you left water heater, dryer or range pilots on,
allow for them in calculating correct furnace gas
input. A quick way is to allow 1,000 BTU per hour
for a water heater, 500 BTU per hour for dryer and
500 BTU per hour for each range burner pilot.
Example:
If you left gas water heater, dryer, two range burner
pilots and one oven pilot on, allow:
Water heater pilot 1,000 BTU per hour
Dryer pilot 500 BTU per hour
2 range burner pilots 1,000 BTU per hour
1 range oven pilot 500 BTU per hour
3,000 BTU per hour
Subtracting 3,000 BTU per hour from 124,138 BTU
per hour measured above equals 121,138 BTU per
hour. This would be the correct furnace gas input
after allowing for pilots left on.
10. Manifold pressure may be adjusted within the range
of 3.2 inches W.C. to 3.8 inches W.C. to get rated
input ± 2 percent. See Section 17, "Manifold
Pressure Adjustment". If you cannot get rated input
with manifold pressure within the allowable range,
you must change orifices.
PROPANE (LP) GAS INPUT RATE
1. Make sure you have proper main burner orifices.
2. Gas supply pressure must be between 11 and 13
inches W.C. for propane (LP) gas.
3. Start furnace following "Operating Instructions" on
front door.
4. Let furnace warm up for 6 minutes.
5. Adjust manifold pressure to 10.0 W.C. ± 0.3 inches
W.C. See Section 19, "Manifold Pressure
Adjustment".
WARNING
Propane (LP) gas installations do not have
gas meters to double check input rate.
Measure manifold pressure adjustment with
an accurate manometer. Failure to accurately
adjust pressure could cause heat exchanger
failure, asphyxiation, fire or explosion,
resulting in damage, injury or death.
WARNING
Do not set Propane (LP) manifold pressure at
11.0 inches W.C. It could cause heat
exchanger failure.