Beckett RWF40 CG15 Manuel D’Utilisation

Manifold to Furnace Pressure information can be used to 
estimate the burner’s fi ring rate when it is not possible to 
clock a meter for the rate.  

To estimate the burner’s fi ring rate:

Measure the furnace pressure over fi re 
Measure the manifold pressure (at the manifold 
pressure test connection).  
Subtract the furnace pressure from the manifold 
pressure 
Compare the result to the data in Figures 14A, 14B, 
or 14C as appropriate for your burner.

Before you clock the meter you must make sure that the 
burner is operating at a steady rate, and that it is the 
only thing that is using gas that would fl ow through the 
meter.

Locate the dial that moves the fastest and determine 
how many cubic feet are represented by one 
revolution of its dial.  
Use your watch for timing and observe how many 
cubic feet are used in one minute.  
Multiply by 60

Example: The dial is a one cubic foot dial, and goes 
around 7 ½ times in one minute.  That gives 7.5 cubic 
feet per minute.  Multiply by 60 to get 450 cubic feet per 
hour (CFH) as your uncorrected fl ow rate.  

Gas is compressible, the higher the pressure on it, the 
smaller the number of cubic feet it occupies.  To correct 
for that you will need to know the gas pressure at the 
meter.  

If there’s a gauge at the meter, read it while the gas 
is fl owing.  (If not, measure the gas pressure in the 
line downstream of the meter before any valves or 
regulators, with no gas fl owing.)  
Convert the gas pressure to PSI if you measure it in 
any other units.  (1 PSI = 27.7 inches water column)
Add 14.7 to the meter pressure, divide their sum by 
14.7, and multiply that result times the uncorrected 
fl ow rate to obtain the pressure corrected fl ow rate.

Example:  The meter in the example above is operating 
at 14” WC.  
14 / 27.7 = 0.5 PSI at the gauge; 14.7 + 0.5 =15.2; 15.2 / 
14.7 = 1.034 correction factor;
1.034 x 450 = 465 CFH corrected for pressure

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Gas volume also changes with the temperature of the 
gas.  Most gas meters are temperature compensated.  
They say so on the face of the index and don’t require 
temperature correction.  The temperature we correct to 
is 60° F.  That’s close to the temperature of the ground, 
so usually it’s not necessary to correct for temperature 
from underground lines.

Measure the gas temperature at the meter.
Add 460 to the gas temperature and divide 520 by 
the result to obtain the correction factor.
Multiply the pressure corrected fl ow rate times the 
temperature correction factor.

Example:  The meter in the example is connected to 
an above ground line on a hot day and shows 100° 
F gas temperature.   460 + 100 = 560; 520 / 560 = 
0.929;  465 x 0.929 = 432 CFH corrected for pressure 
and temperature.  This fi gure is often called SCFH (for 
standard cubic feet per hour).

The BTU content of natural gas varies from one location 
to another, and even from day to day at a fi xed location.  
For fi ring estimates it is usually assumed to be 1000 
BTU’s per standard cubic foot.
To calculate BTU/Hr fi ring rates multiply SCFH times 
1000.
Example:  432 SCFH x 1000 = 432,000 BTU/Hr.
MBH stands for thousands of BTU’s per hour.  Since 
1 cubic foot of natural gas contains 1000 BTU, 1 MBH 
equals 1 SCFH of gas fl ow.
Example:  432 SCFH = 1,080 MBH

The BTU content of LP gas varies with the relative 
quantities of propane and butane in each delivery of gas 
and changes as liquid level in the tank falls.  For fi ring 
estimates it is usually assumed to be 2,500 BTUs per 
standard cubic foot. 
To calculate BTU/Hr fi ring rates multiply SCFH times 
2,500.
Example:  432 SCFH x 2500 = 1,080,000 BTU/Hr.
MBH stands for thousands of BTU’s per hour.  Since 1 
cubic foot of propane gas contains 2,500 BTU, 1 MBH 
equals 0.4 SCFH of gas fl ow.
Example:  432 SCFH = 1,080 MBH

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