Another Friendly Friday Fail!

In this blog we will look at a restaurant Evolve Mechanical Solutions was hired to design.  The following photos were taken during construction and are of the hood, grease duct, access panels, ecology unit/ kitchen exhaust fan and the louvre.

In the picture below we have the hood on the far right, grease duct connecting to it and traveling left to the ecologizer/ kitchen exhaust fan (out of view).

The first mistake is fairly obvious… the trade installed the t-bar butt up against the grease duct access panel. There is no way a ASTTBC certified grease duct cleaner could do a proper job.  The other issue here is that the t-bar is considered limited combustible thus you need to maintain 3” clearance. However the fault could arguably lie with the HVAC trade as NFPA-96 states to place a sign on the grease duct stating do not obstruct.

  • NFPA-96, section 7.1.6:  A sign stating the following shall be placed on all access panels: ACCESS PANEL – DO NOT OBSTRUCT

SOLUTION:  Pull back the t-bar such that a cleaner has access


The following photos are of the grease duct access panel and the ecologizer/ kitchen exhaust fan section.


There are a few issues here:

A) The fasteners (screws) penetrate into the grease duct, which is a big no no in NFPA-96.  This is primarily because of two things; first the grease in the air stream may build up on the screw and secondly it’s not a liquid tight seal.  That is grease, smoke and fire could escape from these penetrations

  • NFPA-96 Section: Fasteners, such as bolts, weld studs, latches, or wing nuts, used to secure the access panels shall be carbon steel or stainless steel and shall not penetrate duct walls.

SOLUTION: Evolve Mechanical Solutions worked with a reputable trade to provide the following detail:

B) There is no sealant or gasket between the duct and access panel.  Any time you have two separate metal components fastened together by screws there needs to be a sealant between them to protect against leakage of grease, smoke and fire.

  • NFPA-96 Section: Access panels shall have a gasket or sealant that is rated for 1500F and shall be grease tight.

SOLUTION:  Install Thermeez Woven Ceramic Tape, which can be purchased at CaptiveAire.

C) The connection to the ecologizer/ kitchen exhaust fan.  Again screws are used to fasten the grease duct to the ecologizer.  Same issues may arise as the screws used to install the access panels.  However the bigger concern is overtime the screws will fail due to the heating and subsequent cooling of the duct/ ecologizer connection. The reason why is that the screws will expand on heating and contract on cooling and after 1000’s of cycles it will eventually become loose and fail.  

  • NFPA-96 Section: In-line fans shall be connected to the exhaust duct by flanges securely bolted as shown in Figure through Figure or by a system specifically listed for such use.

SOLUTION:  Follow and install as per the manufactures and NFPA detail below:

The photo below is of the grease duct as it penetrates the building envelope.

The issue here is the grease duct is butt up against limited combustible wall.  NFPA requires 3″ separation from limited combustibles and the grease duct in order for it to not catch fire.

NFPA- 96 Section 4.2.1: Where enclosures are not required, hoods, grease removal devices, exhaust fans, and ducts shall have a clearance of at least 457 mm (18 in.) to combustible material, 76 mm (3 in.) to limited-combustible material, and 0 mm (0 in.) to noncombustible material.

SOLUTION: Remove the dry wall around the grease duct and install a non-combustible material to cover the 3″ space such that it’s concealed.

Finally the photo below is of the louvre

In the event of a fire the ecologizer/ kitchen exhaust fan will turn on to high speed to remove smoke and flames from the building.  The will be exhausted out of a louvre similar to this one below.  The issue is if patrons are below this they may suffer burns and smoke inhalation.  NFPA requires the louvre’s blades to be either horizontal or angled upwards at 45 degrees to minimize and burns or smoke risks to the public.

NFPA-96 Section 7.8.3:  Wall terminations shall be arranged with or provided with the following properties… Sentence (4) The exhaust flow shall be directed perpendicularly outward from the wall face or upward.

SOLUTION: Replace the louvre with one that has either horizontal or vertical blades

James Hicks P.Eng.

Evolve Mechanical Solutions


#Restaurant #HVAC #Fail