1. Professional Member
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Sep 2004
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Does anyone know if there is a way to clock a rotary gas meter? Otherwise, does anyone know how to determine the gas consumption (cfh) of a modulating direct fired burner at high fire?

2. Regular Guest
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Jun 2004
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Maryland's Eastern Shore
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Not sure what you mean by rotary, does it have a cubic foot hand??? Half a cubic foot??? Two???

3. Professional Member
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Sep 2004
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There are no clocking dials on it. I know how to clock a diaphram meter, but I'm stumped on this one. The designations on these meters are 2M, 5M, or 11M. This indicates the maximum capacity of the meter in millions of BTUH.

4. rubobornot Guest
Thats a good question, could you take 1.1 X CFM X TD , that would give you the btuh output of the burner. and then divide that by the btu content of the gas to get the CFH on high fire and low fire .In KC MO they claim it is around 1000 per cubicfoot of natural gas. so if you had a temp rise of 120 degrees with 4000 cfm of air that would be 528,000 btuh divded by 1000 or 528 cfh. CFM can be found by dividing the btuh in put of the burner by 1.1 X TD. So if you took 528,000 divided it by 1.1 X 120 you would get 4000 CFM.

5. acc
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Feb 2003
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would this be a roots meter,with a digital read out?,
im curious to on how to read these-ive seen only one.

6. Professional Member
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Milton Ontario
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Thanks for the replies. Rubobonot, if I have to, I will apply the heat formula. The trouble is in determining the cfm across the burner. I can measure the cfm in the duct by pitot tube, but I really have no way of measuring the cfm that is brought into the duct by the burner fan. It is mounted external to the duct, with a flanged connection. There is no spot to take readings. Manufacturer's literature in this dinosaur is out of the question.....

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