# Thread: Fan Wheel Sizing

1. Professional Member
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I have an air handler that needs more air flow. The capacity was reduced by the installing contractor becasue of noisy air complaints. Now there's not enough air flow to heat the space. I'm getting very high discharge temps and high return temps but a cold space. The unit serves a high bay area and I need more air. The fan motor has a fixed, 4 belt "B" section sheave. I know the fan curve has the capacity for more flow but what I don't know is how to figure out what size motor sheave I need to get a 25% increase in air flow.

Any pointers?

2. The formula is:

RPM1 over RPM2 = PD2 over PD1

Where RPM1 is the motor
RPM2 is the blower
PD1 is the motor sheave
PD2 is the blower sheave

Solve for ratio then multiply for % increase.

Regards.......

[Edited by gonefishing on 01-09-2006 at 07:44 PM]

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gone fishing

you not gonna tell him about wether or not the motor has the room for it? hehe!

4. Nope, gotta figure if he reads fan curves
he has an ampmeter

5. Originally posted by gonefishing
The formula is:

RPM1 over RPM2 = PD2 over PD1

Where RPM1 is the motor
RPM2 is the blower
PD1 is the motor sheave
PD2 is the blower sheave

Solve for ratio then multiply for % increase.

Regards.......

[Edited by gonefishing on 01-09-2006 at 07:44 PM]
Or...in an easier to remember form....

RPM1 X PD1 = RPM2 X PD2

Jogas

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Thanks fellers, you've saved my bacon. What's an amp meter? (tee hee)

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I thought the formula for rpm to static pressure is rpm2 new divided by rpm old that ratio times itself then times original static pressure gives you new esp.

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