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Food for Thought - Rapids' Blog
Proper Kitchen Ventilation - How To Order A Vent System For Your Restaurant
Basics on how vent hoods work, how to size them and the right questions to ask!
Why Kitchen Ventilation
- Vent hoods can exhaust smoke, heat, steam and grease from the kitchen environment.
- Vent hoods assist in fire prevention by helping to
contain any cook line fire within the hood cavity
- Vent hoods can have fire suppression systems built
in and the means to shutoff natural gas supplied to
the cook line
- By exhausting grease, heat, steam and smoke, vent
hoods create a healthier environment for the kitchen
Common Components of a Vent System
- At a minimum, a vent system has an exhaust hood and an exhaust fan that draws the kitchen air through a series of grease filters.
- Vent hoods are always
located right above the
cook line and may also be
used above ware washing
equipment to exhaust
The Restaurant Vent Hood
- The most visible part of the system is the vent hood itself.
- The vent hood is always
made of steel but may be
stainless steel or
- Aluminized steel is similar
to galvanized steel but has a
better finish while still
helping to prevent rust and
Grease Filters For Restaurant Vent Hood
- Grease filters are responsible for extracting the grease from the exhaust.
- The metal slats capture the
heavier grease as the air
- The filters must be
removed and washed
periodically to remove the
Pushing and Pulling Air From Your Restaurant Kitchen
- Vent hoods use powerful fans to draw air out of the hood cavity, through the grease filters and exhaust it to outside.
- Systems may have one or
two fans depending on the
type and configuration.
Types of Restaurant Kitchen Vent Systems
- There are several types of vent hoods available and local code may govern which type is used. The customer is responsible for determining the type of hood that will meet the code requirements of his community.
- Most hood types will fall within two broad
categories: Exhaust only and Exhaust with
Exhaust Only Restaurant Vent Hoods
- As the name implies, exhaust only hoods create only an outflow of air.
- Usually used in kitchens with little or no free grease in the air.
- Often used to vent steam
from ware washing
Shelf Type Exhaust Only Restaurant Hoods
- Shelf type hoods are often used where head clearance is critical since they have no “front” like a box hood.
- Air is drawn through the filters
and then out of the building.
- Shelf hoods mount closer to the
cook line, therefore they should
NOT be used where a char-broiler
is present! The open flame flare up
of a char-broiler could ignite the
grease captured by the hood!
- Shelf hoods are increasingly not
allowed by code in many areas
since they have little ability to
contain a fire. But side curtains of
steel can be added.
Exhaust Only Canopy Hood For Restaurant Kitchen
- The Canopy hood is completely enclosed front, back, sides and top.
- Canopy hoods have a far greater ability to contain a cook top fire.
- By adding the front panel, canopy hoods evacuate more air from the space above the cooking line rather than from the entire room.
Restaurant Exhaust Hoods With Make Up
- By adding outside air into the kitchen environment, a stronger draft is created over the cook line.
- Referred to as make-up air,
the outside air supplies
80% of the air that is
exhausted through the
hood. The remaining 20%
is pulled from the kitchen
Make-up and Exhaust Airflow
- The blue arrows indicate the flow of air created by the supply fan on top of the building, 80% of the air exhausted.
- The green arrow shows the
20% of exhausted air that
comes from the kitchen
- The red arrow indicates the
airflow out of the kitchen
and through the filters and
Benefits of Make-up Air
- By supplying only 80% of the total air exhausted, a slight vacuum is created that captures the heavier, grease laden air of the kitchen.
- The filters are more
efficient at grease removal.
- Far less cooking odor is
noticed in the dining area.
Rear Plenum Make-up Air
- Supplying the make-up air through a flue (plenum) that runs down the back of the cook line has many benefits.
- 80% of the exhausted air
passes through the cook line
collecting more smoke and
- The plenum provides the
fireproof back wall that fire
code requires in most
Rear Plenum Airflow
- The 80% and 20% proportions remain the same. However in this system, 80% of the exhausted air moves directly through the cook line capturing even more smoke and grease.
- With their increased
efficiency and built-in fire
proof rear wall, rear plenum
exhaust systems are
becoming the industry
standard and the favorite of
building code inspectors
Cold Fact on Supply Air
- It is a fair assessment that adding outside air into a vent hood is desirable in many ways: greater efficiency, better ventilation etc. There is one major drawback – dumping raw winter air into the kitchen!
Tempered Make-up Air
The solution to the super-cold winter air problem is
to add a small furnace to the make-up air supply
duct. This may seem counterproductive to heat air
just to pump it out of the building, but this is a
decision point best made with the comfort of the
cook in mind! Is it less expensive to heat the air
compared to constantly hiring to replace a
frostbitten cook? (Most of these furnaces only run when
the outside temperature is below 32 degrees and the hood’s
fans are on. On average, 75 days a year in Iowa for
How to Size a Restaurant Vent Hood
- Now that we have looked at several common hood types , we need to decide what size system the customer needs.
- For the most part, we are only concerned with the
size of the physical hood itself, the manufacturer’s
engineers will suggest the correct sizes for the
supply or exhaust fans once we supply them with
- If the hood is for new construction, the customer’s
HVAC contractor should be supplied with the CFM
ratings of all exhaust and make-up air fans!
Minimum Size Standards For Your Kitchen Restaurant Hood
While building and fire codes vary from one community to the next, there are some standards.
- It is generally recognized that a vent hood’s length must overhang the cook line by 6 inches on each end.
- This overhang helps contain
any fire that starts on the
- This is a minimum
community may require
More on Sizing Your Grill Hood
- Once installed, the lower edge of the kitchen's grill hood must be between 78” and 84” above the finished floor.
- Less than 78” and there is
not enough headroom to get
under the hood to work.
- More than 84” and there
isn’t sufficient exhaust
velocity near the cook line to
pull grease and smoke into
Depth of Your Restaurant Vent Hood
- The depth of a vent hood (front to back) can be sized to fit the customer’s need.
- Like the length, the depth
should be 6” to 12” deeper
than the cook line.
- Most vent hoods are either
48” or 54” deep. The deeper
hood is used when steam
generating equipment is
present. The added depth
allows for steam capture
since this equipment tends to
open from the front.
Height Necessary For A Vent Hood
- Compared to length and depth, height is actually fairly standard.
- Canopy hoods and shelf
hoods should be
minimum 24" high at
exhaust compartment to
properly contain smoke
and grease laden
Sizing the Exhaust and Make-up (Supply) Fans
- The Rapids catalog shows comparable hood lengths and the suggested fan size ratings.
- Please remember that these are suggestions! The manufacturer should be supplied with the desired hood size and also a drawing and description of the cook line.
- The manufacturer’s engineers will confirm the correct fan sizes needed.
Required and Optional Accessories For Your Restaurant's Kitchen Ventilation
- Ventilation systems have many accessories available: Fire suppression systems, roof curbs for the fans, gas valve controls, fan speed controls and more.
- What may be an optional accessory in one community may be required equipment in another. Again, the customer must determine what their local code requires.
Fire Suppression (Ansul System)
- Much like a sprinkler system is needed for the dining area, a sprinkler system is needed over the cook line.
- These systems may be pre-plumbed at the factory, or purchased from, and installed by, a local contractor.
- If the factory is to install the system, they must be provided with a measured drawing of the cook line.
- Fire suppression systems are each different and must be price quoted case by case.
Common Fire Suppression Components
Other than the visible nozzles under the hood, fire suppression systems typically have:
- A gas shut off valve.
- Fire curtains that seal off the air ducts.
- A chemical pack of fire suppression material.
- Emergency pull switches that can be manually activated.
- A roof curb is a small box-like curb that the exhaustor supply fan sits in. The purpose of the curb is to contain any grease that makes it through the vent hood filters and is then expelled by the fan.
- The curb area must be cleaned periodically to prevent a fire hazard.
- Curbs are required by code in all communities.
Fan Speed Controls On Your Restaurant's Ventilation System
- In some cases, a vent system can have a two position speed control installed.
- Usually speed controls would be found on systems that have extended periods when grease producing equipment is not being used, but other heat or steam producing equipment is in use.
Side Curtains On Your Restaurant Vent Hood
- Earlier we learned that there must be a 6” overhang on the end of the vent hood versus the length of the cook line.
- If this isn’t physically possible, some communities will allow hood to floor steel panels (curtains) to be installed on the ends of the hood as a fire containment solution.
Light Options On your Restaurant Vent Hood
Vent hoods all come with incandescent lighting, but the number of fixtures may not satisfy the customers needs. Before manufacturing begins, additional lights can be specified in the new hood.
How To Order A Vent System For Your Restaurant
- With so many variables, it can be difficult making sure you have covered all the bases. Rapids has developed a Vent System Sign - off Sheet to assist with placing an order.
- Since vent systems aren’t returnable, it is required that the customer sign off on our checklist, the manufacturer’s drawings and any change orders that may happen along the way.
- Most vent systems require 3 to 5 weeks in factory for production after the signed drawings are returned! Please be aware of all of the steps required to get an order underway!
- When a customer first inquires about a vent hood, Rapids uses a sign -off sheet to make sure we ask all of the necessary questions.
- The sign-off sheet is then used as the quote request to the manufacturer.
- Once the quote is completed by the manufacturer it is faxed or mailed the customer for their signature. We cannot proceed without a signed copy of the sheet.
- A few days after quote acceptance the manufacturer will send a drawing of the proposed vent system. This is the final check for compliance. THE CUSTOMER MUST SIGN OFF ON THE DRAWING, Not the Salesperson!
- Once both the initial sign-off sheet and the manufacturer’s drawing have been signed and received by the manufacturer, the factory production begins.
- These are critical steps we cannot skip so that we can assure the customer they are getting exactly what they ordered.
Vent Hood systems:
- Remove smoke, grease, heat and steam
- Help control kitchen fires
- Create a healthier kitchen environment
Vent systems come in two basic types:
- Vent systems come in two basic types:
- Exhaust with compensating make-up air
Exhaust only systems:
- Have only one fan
- Tend to be used in kitchens where little grease is produced.
- Are common over ware washing equipment to vent steam.
Exhaust with Make-up air (compensating hoods)
- The flow of outside air into the hood creates a slight vacuum that captures more grease within the hood.
- Greatly reduces cooking odors in the dining area.
- More efficient than systems without make - up air.
Sizing a vent hood
- The vent hood must extend at least 6” beyond the length of the cook line.
- The front to back depth of the hood should be at least 6” greater than the depth of the cook line.
- The height from the floor to the bottom edge of the hood must be between 78” and 84”.
- The standard height dimension of a vent hood itself is 24”.
- Local codes must be followed when sizing a hood.
- The fan(s) sizing will be confirmed by the factory engineers.
Required and optional accessories:
- Roof curbs.
- Fire suppression systems.
- Two speed fan controls.
- Side curtains.
- Additional light fixtures
- Local code may make any one of these options arequirements
The Order Process
- The Rapids sign-off sheet must be signed by the customer.
- The sign-off sheet can be used to get a quote.
- After the order is placed, the manufacturer will send a drawing that must be signed and returned by the customer. The salesperson cannot sign off!
- Once both the Rapids sign-off sheet and the signed drawings have been received by the manufacturer, factory production begins.
- Most vent hood systems take 3 to 5 weeks to produce after the signed documents are received.