1. ## Determining Gas Input

So I know how to determine gas input in a residential application. But I am in a light commercial role and would like to know how you determine gas input when you have a rather large building that you can’t just go around and cut fuel off to appliances.

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Errr. Rating plates?

3. Next to impossible. You can get exact airflow measurements, check delta t and plot it on manufacturer chart or use btu = cfm x deltaT x 1.08 and account for efficiency of the furnace

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Clock the meter

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5. Originally Posted by Spitz
Clock the meter

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I understand that, but how do you clock a meter at a place that can’t have all of the gas equipment shut down? Is there a meter of sorts that can be put in line to the equipment

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Could buy one on ebay for \$100

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7. Originally Posted by Spitz
Could buy one on ebay for \$100

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What kind of meter is it

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One like on the side of a house

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9. How do you determine the btus on commercial equipment when you can't clock the meter? What about LP?

10. Originally Posted by Jim Davis
How do you determine the btus on commercial equipment when you can't clock the meter? What about LP?
Analyzer. 6-9% or 3-6% depending on burner

Btu = cfm x deltaT x 1.08

Or

Btu = gpm x deltaT x 500

Can i get my recertification card now?

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11. Originally Posted by gravity
Analyzer. 6-9% or 3-6% depending on burner

Btu = cfm x deltaT x 1.08

Or

Btu = gpm x deltaT x 500

Can i get my recertification card now?

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Wouldn’t you need to know BTU to determine CFM? And to get GPM would you not need to clock a meter? Or would total static be good enough for the situation

12. ## Determining Gas Input

For CFM use a flow hood, traverse the duct with pitot tube, or hot wire anemometer, or take TESP and use the manufacturer blower curve chart to plot CFM.

For GPM, take deltaP across pump, boiler, unit and convert to ft/head. Use a pump curve chart or manufacturer chart to plot GPM using head.

Then fill in the formula

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13. Originally Posted by dustinwest
Or would total static be good enough for the situation
Static pressure or duct traverse will work.

As long as you get an accurate CFM reading the formula will tell you if your BTUH output is within the rated output of the unit.

Output is the only important number anyway.

If output isn’t correct, adjust manifold pressure or change the orifices as necessary.

Be sure you are using a combustion analyzer when making any adjustments.

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