Roof Exhaust Fans come in many shapes and sizes. Most exhaust fans will fall under the category of either a Centrifugal or Axial roof exhaust fan. Axial roof exhaust fans draw air straight from inside your building into the fan and straight out. The air stream does not change direction inside an Axial Roof Fan and the discharge is typically straight up into the atmosphere, up and away from the roofs surface. Although there are exceptions such as hooded axial exhaust fans which discharge back to the roof and give a little more protection against adverse weather situations such as ice or snow. Axial roof fans are often used on non-ducted applications and where static pressures are relatively low – there is an abundance of supply air available.
Upblast Centrifugal Roof Exhaust Fans are often used for contaminated air streams where grease or moisture may exist such as restaurant hood exhaust or laundry room exhaust. The motor and wiring are typically out of the air stream and there is a grease or moisture drain located at the bottom of the fan. Centrifugal Roof Exhaust Fans do well as the static pressure increases like you will find in a restaurant hood application where the air stream needs to be pulled through grease filters and ducting increasing the resistance or static pressure before it reaches the fan. Downblast Centrifugal Roof Exhaust Fans are typically selected for general exhaust applications such as bathrooms or small warehouses where the air stream is clean.
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