Hi, I am getting rusty. We know that for air flow through a fan, in English units under typical conditions, the Bhp required is calculated as:

BHP = (CFM * Pressure) / 6356 * Eff), where pressure is in inches of water and Eff is the fan efficiency.

We also know from Bernoulli's equation that, if we ignore changes in elevation:

P1 + KE1 + Energy Input = P2 + KE2

My understanding is that we can assume the air out in the room somewhere is essentially not moving, so we have Energy Input = (P2-P1) + KE2.

Here's what's driving me batty. I am trying to derive the 6356 constant and can't seem to do it. Am I missing something? Wrong approach? The units get scrambled on me.

Any advice would be appreciated.