Bard W24G4 Installation Instructions Manual page 30

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 the location from local
supplier. A stopwatch will be needed to measure
actual gas input.
1. Gas supply pressure must be between 5" and 7"
W.C. for natural gas.
2. Turn off all other gas appliances. The pilots may
be left 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 =
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 =
29
If no other pilots were left on, this is the furnace
gas input.
9. If the water heater, dryer or range pilots were left
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.
Manual 2100-721B
Page 30 of 54
Example:
If the gas water heater, dryer, two range burner
pilots and one oven pilot were left on, allow:
Water heater pilot
Dryer pilot
2 range burner pilots
1 range oven pilot
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" W.C. to 3.8" W.C. to get rated input
± 2 percent. See Section 19, "Manifold Pressure
Adjustment." If rated input with manifold pressure
cannot be gotten within the allowable range,
orifices must be changed.
Propane (LP) Gas Input Rate
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.
1. Make the main burner orifices are correct.
2. Gas supply pressure must be between 11" and 13"
W.C. for propane (LP) gas.
= BTU/hour
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".
See Section 19, "Manifold Pressure Adjustment".
= 124,138 BTU
Do not set propane (LP) manifold pressure
at 11.0" W.C. It could cause heat exchanger
failure.
1,000 BTU per hour
500 BTU per hour
1,000 BTU per hour
500 BTU per hour
3,000 BTU per hour
WARNING
WARNING