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GAS INPUT RATE:
The gas input rate of this water heater is affected by several environmental factors such as:
•
The heating value of the gas
•
The air and gas densities (which vary widely due to barometric pressure and temperature changes).
•
Venting installations (pipe diameter and length)
When measuring the input rate these factors should also be incorporated into the calculations. Also measure the gas consumption over a sufficiently long time to
obtain an accurate gas consumption rate (eg 3-5 minutes, not one revolution of the meter needle).
Long vents, and vents with many elbows, inherently reduce the gas input rate due to increased resistance to moving combustion air and flue gases. Because the
system resistance is increased, the vacuum which causes the gas to flow through the gas orifice is reduced the input drops correspondingly. The short vent
typically runs at the rated 100,000 BTU/H; whereas the maximum vent will see the input drop to around 94,000 BTU/H. The approximate relationship is shown in
the graph to the right.
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