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.