Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Grease Exhaust Duct Friction

Grease Exhaust Duct Friction

Grease Exhaust Duct Friction

I am looking for friction information on grease-laden welded black iron ductwork for a kitchen hood exhaust. I need to have a certain static at the hood collar and am trying to size up the roof fan. Something tells me that most people just use the galvanized ductulator slide rule for this type of application, but it that acceptable? If not, what is typically used to size grease exhaust ductwork and calculate required fan static?

RE: Grease Exhaust Duct Friction

Design you exhaust system in accordance to NFPA 91, a standard for exhaust system including kitchen hood exhaust. Once you have determine your system CFM based on air velocity in the duct per NFPA 91, then you should be able to calculate by hand, friction losses and determine fan size based on fan characteristic curve. A few things to keep in mind are 1)the capture velocity of the fumes over the cooking appliances 2) if energy conservation is important particularly in the cooling season, consider a push pull system 3) many communities in the US require stainless steel for the kitchen hood; for exhaust ducts, check with your community building inspector.

RE: Grease Exhaust Duct Friction

Thank you, but I have been unable to locate and good friction information for greasy black iron duct. Any ideas?

RE: Grease Exhaust Duct Friction

As an uninformed guess, a friction factor or % blockage would depend on indoor air quality and particulate- if there is only grease to stick to it, roughness ~ drop size. If someone is ventilating a deep fryer in shared space with for the sake of discussion, a stable, filter or duct loading could be a big problem.

RE: Grease Exhaust Duct Friction

Bron y r Aur,
Why are you making a grease duct out of Black iron , I have always made them out of 14guage welded galvanized sheet.
If you are relying on the grease in the duct to protect the iron , it does not work, there is always some moisture and the ducting rusts. So at the very least you will need to paint the duct, then calculate your friction for a painted surface.

You are judged not by what you know, but by what you can do.

RE: Grease Exhaust Duct Friction

NFPA-96 calls for welded carbon steel or stainless ducts. Never heard of galvanized being used for kitchen exhaust.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close