Exhaust Hoods

Many players, many opportunities for failure.

Restaurant kitchens generate heat, smoke, grease and odors. No surprise here. How you deal with these conditions needs considerable thought, smart design, proper engineering and a well -coordinated effort among your entire design team.

Let’s not get into the weeds here discussing the nuances of different hood systems, air handling – exhaust and make-up air – systems or hood features.  This is a more generic discussion of key pitfalls that you, the owner, operator, or developer need to be aware of.

Most jurisdictions require venting over cooking appliances that generate, heat, smoke, grease, steam/condensation.  We will leave the discussion of types of hoods to more technical articles. This is the 10,000-foot view that will help avoid operational issues.

Space planning:  It makes sense to consolidate equipment that requires venting. Arranging workstations that can fit under a common hood or back-to-back hoods, or adjacent hoods allows for them to be ducted together to consolidate duct routing and fans.

Ceiling heights and clearances: Vertical clearances are frequently overlooked. You may think you have ample space when you look at floor to ceiling structure dimension. But add in ductwork, support structures to hold the ductwork, utilities that may cross over or under these items and you lose height quickly.

Low ceilings may require alternate styles of hoods which can impact the types and height of equipment you can fit under the hood.  Sloped front hoods (designed for low ceiling applications) or back shelf hoods, may prevent the use of tall appliances – ovens, rotisseries, tall grills.

Hood construction: Hood assemblies can be very long. If longer than 16’ or if building conditions or access require shorter lengths, they may be assembled from several hoods joined together.

Hoods are large and may need to be assembled in sections to fit in the building or through doors and around corners. Even though you may have less than 16’ of hood length, the hood may still need to be two or more sections.

These sections, when joined together, and will have seams where the multiple hoods meet.  With standard hoods that are eighty inches off the floor, these intermediate panels are not an obstruction.  However, with sloped front hoods or back shelf hoods, the sides of the hoods creating the seam may affect the placement of tall equipment.  Accurate equipment drawings showing, in elevation view, how the equipment fits under the hood and showing the actual hood design, will expose this potential conflict.

Fire Protection:  Those pipes that hang down from the hood for the fire protection system are unsightly and often, in the way.  But they are required for life safety and are a non-negotiable requirement.  There are, however, ways to mitigate their visual and operational impact.

Overlapping fire protection: When you specify overlapping fire protection, the system is designed with greater capacity and tighter spacing of nozzles. But the nozzles are mounted higher and not so obstructive. Additionally, equipment under the hood can be rearranged without having to relocate nozzles (requiring a certified technician, scheduled and costly).

Water systems:  Solid fuel cooking or hoods located in high rise buildings may be required by code to have a continuous source of fire suppressant vs the traditional chemical system that has a limited capacity.  These systems often use a water mist and a surfactant (soap) to suffocate a fire and run off the building water line.  These systems require additional floor drains or floor sinks for their periodic wash down cycles and for water capture when the system is activated.  These are large drain lines (2”+-) that extend from the hood gutter to the nearest floor sink.  Careful placement of these drains is required to avoid equipment legs or casters or being a trip hazard in a corridor. Additionally, they may be considered unsightly by the design team and need to be strategically located or run through the wall to a drain on the back side of the cook line.

Location of Suppression tanks, controls and pull stations: Hood fire protection systems require control panels and/or tanks of chemicals.  These are mounted either on the end of the hood, if room permits, or on an adjacent wall.  When mounted on a wall, it is important to place the tanks as close to the hoods as possible as there are limitations in the length of pipe from the tanks to the nozzles. They should be high as possible to avoid conflicting with wall shelving , the location of these appliances must be shown on your drawings to avoid losing wall space for storage.

Pull Stations: Similarly, these systems need ‘pull stations”. These are essentially the alarm and activation switch if the system needs to be activated manually.  These are located for easy access in the path of travel from the hood to the exit.  Fire marshals often approve this location. Coordinating the installation of the hood fire protection system is needed to avoid having exposed piping in your kitchen.  If this trade is called in after the walls are finished, they will surface mount their pull stations and cable conduit.  While not illegal, this is unsightly, often difficult to clean around, and protrudes out into hallways or work areas.  Insist and note on your drawings that these systems must be installed inside the walls with flush mounted pull stations.

The design coordination of the kitchen exhaust system, hood design, hood installation and installation of the hood fire protection involves:

Kitchen designer – provides the equipment layout and often works with a hood vendor to engineer the hood overall length, exhaust and make up air systems, pollution control units if required and fire protection.  Their drawings and elevations should correctly show this hood over the cooking line equipment, including the hood end panels if several hoods make up the overall length.

Mechanical / Electrical Engineers – take and review this hood engineering information and design the ductwork, utilities, fan placement and needed controls. Their drawings and specifications will show this equipment.

Mechanical Contractor – Purchases the hood package (sometimes provided by owner or kitchen equipment vendor) and installs the system per the drawings and specifications.

Electrical Contractor – installs necessary power and controls. Often requires hood manufacturer tech support to coordinate control wiring.

Fire Protection Installer- Usually a sub-contractor under the hood manufacturer or a separate supplier working under the mechanical contractor. His scope and scheduling often falls through the cracks and need to be highlighted during weekly construction meeting.  Their work needs to be staged, phase one rough piping IN WALLS for pull stations, and final connection after equipment is set and walls finished.

General Contractor – Coordination of all the above. Identifies any field conditions that may affect this design, schedules the work and all required inspections.

Lots of opportunities for failure. Just don’t let it happen!