Grease ducts in Commercial Kitchens serve as the roadway to transport the products of combustion from cooking away from the indoor environment to the outdoors.  NFPA-96 has some strict standards as to how a grease duct may be installed.  In the following restaurant fail we will focus on how to correct one major issue: A low point (dip) within the grease duct.



The picture above is of a Commercial Kitchen grease duct.  To the right it slopes upwards and connects to the kitchen hood.  To the left the grease duct goes up through the roof to the inlet of the kitchen exhaust fan.

The issue is right in the middle, there is a low point or dip in the grease duct.  The issue here is overtime grease may collect and build up; if a flame should touch it, it could ignite.

NFPA-96-14 states:

7.1.4 All ducts shall be installed with a minimum 2 percent slope on horizontal runs… All ducts shall be installed without forming dips or traps.



The Solution: Although not ideal and only acceptable if re-installing the grease duct is not possible and the risk is low.  NFPA-96 says if we do have a dip or low point in the grease duct we may drain it as long as said drain is continuously welded to the grease duct in order to keep it liquid tight.

NFPA-96-14 states:* Drains shall be provided at low points in horizontal ducts. Where provided, drains shall be continuously welded to the exhaust duct…


In this particular case we drained the grease duct back to the hood plenum where it may drain into the hoods grease cups.

Let us know if you have any Commercial Kitchen questions or problems you need a hand with

James Hicks P.Eng

Evolve Mechanical Solutions