Does Fan Air-Moving Capacity Change When Fan Wiring is Reversed to Operate in Opposite Direction

Question:

When reversing wires to make vent fan work in opposite direction does this reduce the cfm/airflow?

asked by: RYAN M

Expert Reply:

Reversing the polarity of the wires to the motor on a fan will certainly let it operate in reverse direction. Whether this reduces the amount of air-moving capacity in cubic-feet-per-minute (CFM) depends on the nature of the fan blades. Most fans, including the Ventline Vanair # VP-543SP, have fan blades that are oriented in a specific direction because their primary purpose is to exhaust hot air out of the trailer.

It is absolutely safe to wire the fan in reverse polarity - I confirmed this with my technical contact at Ventline - and with this fan the air-moving capacity will be reduced to some degree. Since Ventline has not tested the fan in this mode of operation they could not give me a specific CFM rating for the reverse operation.

expert reply by: Adam R