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I'm trying to remember the formula for calculating the CFM of a indoor split system air handler. I know that you're supposed to take the amp draw of the unit, and the delta T between the supply and return, but what is the formula that you plug you info into to figure out how much CFM you are getting across the coil/heat strips? HELP ME PLEASE!

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CFM = Load / 1.1 x TD

This is a sensible heat equation for airflow requirements.

3. CFM = volts x amps x 3.414 / 1.08 x temperature rise

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Chillbilly;

I your TD the same as delta Temp across the evap?

What about the CFM for a gas furnace?
thanks
gn

5. CFM = btu output/ 1.08 x temperature rise

P.S. your temp rise is not across the evap, it is across the heating elements or heat exchanger.

P.P.S. volts x amps x 3.414 = btu output on electric furnace

[Edited by key on 05-18-2005 at 06:46 AM]

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That's the one. Thanks a million.

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The accuracy of the measurements can make a large difference,using this method.

A manometer and fan data chart,is a lot easier and more accurate,IMHO.

8. dnt
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I fooled with those calculations to determine CFM several years ago, I finally gave up and went and bought a good quality Pitot tube airflow tester, a good traverse on the main supply trunk will eliminate all the guess work.

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## CFM testing problem

In my refigeration book the cfm calc formula is CFM=BTUH/1.1XTD on my test they used BTUH input (Not Output) and at sea level. What is up with this.
I have also seen 1.0505 and 1.08 as numbers in the formula. At any rate my answers were not the same as those given to chose from.

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