# Fan Heat Gain Calculation

I'm looking into the fan heat gain equations in the engineering reference guide, but I don't understand the logic. There are also a lot of missing equation references and things, so maybe the section isn't finished?

Specifically on pg 1051 (V8.8) at the end of section 17.4.2.4 says that fan heat loss to the air: `Qtoair = Hfan +(Hmotor - Hfan) * fmotortoair`

, which I don't understand. H is defined as power [W], so this says that in a condition where `fmotortoair = 0`

, the heat to the air is equal to the total power to the fan (mechanical power to the impeller I assume), which is obviously not true because a large portion of that power is converted to rotational energy. Then if `fmotortoair > 0`

, some of that impeller power is subtracted for some reason from the total.

Any insights into what's going on would be appreciated, because right now this seems incorrect to me.