Are you wondering how to size an upblast exhaust fan
for your commercial kitchen?
At some point, nearly all commercial kitchen and restaurant owners will have to replace an upblast exhaust fan in their kitchen. Calculating what CFM you need is the most crucial part of how to size an upblast exhaust fan for your commercial kitchen ventilation system.
If you don’t already know the correct CFM needed for your fan or the cooking equipment or commercial vent hood system you use has changed, this article will help you determine what size upblast ventilator your system requires.
First, we’ll go over a few basics regarding the importance of CFM and then review what information is necessary for you to provide us so that we can perform a commercial kitchen hood CFM calculation .
Why is CFM so important?
As you likely already know, the airflow capacity of an upblast ventilator is rated in CFM, or cubic feet per minute. If you don’t have enough air movement to be effective, your kitchen could end up very smoky, hot, and your hood, ductwork, and kitchen surfaces could become heavily laden with a coating of un-exhausted grease and oil effluent. This additional build-up makes your ventilation system harder to clean and more prone to igniting a hood or duct fire.
How do I calculate the right CFM and size
for my upblast exhaust fan?
How to properly calculate the size and CFM for a centrifugal upblast exhaust fan relies on knowledge of a few pieces of important information.
1. What is the size of the ventilation hood that the upblast exhaust fan is going to be attached to?
The larger the area of your hood, the harder the upblast roof ventilator has to work to exhaust smoke, grease, and heat from your kitchen. The design and mounting location of your hood may also come into play as they can have an impact on hood performance.
2. What cooking equipment is going to be operated under that hood?
Knowing what cooking equipment that will be used under the hood is important for a few reasons but mainly because of the need to exhaust smoke and grease as well as solid fuel effluent that can cause dangerous creosote build-up in vent hoods and ducts.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has published guidelines for minimum exhaust flow rates (CFM per linear foot of hood) for UL listed vent hoods based on the appliance duty classifications outlines in the ASHRAE Standard 154. The National Fire Protection Association (NFPA) also sets standards for air removal volume, and most municipal regulations will meet or exceed any of these guidelines.
- Light duty appliances includes gas and electric ovens as well as convection ovens and steamers. As an example, the ASHRAE minimum CFM for light duty appliances ranges between 150 CFM to 300 CFM.
- Medium duty appliances includes electric and gas hot-tops, griddles, fryers, conveyor ovens, and rotisseries as well as electric and gas pasta cookers. As an example, the ASHRAE minimum CFM for medium duty appliances ranges between 150 CFM to 400 CFM.
- Heavy duty appliances includes electric and gas underfired broilers, woks, and gas open-burner ranges as well as salamanders. As an example, the ASHRAE minimum CFM for heavy duty appliances ranges between 200 CFM to 400 CFM.
- Extra-heavy duty appliances include those using solid fuel such as wood, charcoal, briquettes, and mesquite to provide all or part of the heat source for cooking. As an example, the ASHRAE minimum CFM for extra-heavy duty appliances ranges between 350 CFM to 550 CFM or more.
In addition to knowing the type of cooking, it is also important to know how the equipment is or will be arranged under the hood. Equipment that is appropriately arranged under your hood can result in up to a 60% savings of CFM, which in turn can save you money. For example, an extra heavy-duty appliance placed at the end of a hood will be more prone to spillage than if it was placed under the middle of the same hood.
The location and style of the hood itself can also make a significant difference. of the If you need assistance in determining the correct arrangement of your cooking appliances or vent hoods, just let us know. We’re more than happy to help you.
3. How much duct work is there between the upblast exhaust fan and the vent hood in the kitchen?
Knowing how much duct work there is between your fan and the hood is a very important part of calculating proper CFM for your upblast exhaust fan. The longer the air has to travel, the more opportunities there are for the air flow to be slowed. The reason that the air flow rate will generally drop along the way from your hood to your fan is because of frictional and turbulence losses. Other duct design considerations that may affect your CFM include the shape of your duct work (square vs. round) and how many twists and turns it needs to take.
4. What is the size of the base of your existing fan or the size of your roof curb?
This last bit of information is probably the easiest to provide. In order to size your centrifugal upblast exhaust fan, we’ll need to know the size of the base of the existing fan. If there is no existing fan, we’ll need to know the size of the roof curb that the fan will be placed on top of. If you are starting from scratch, plant to side mount your fan or simply don’t have that information, there’s no need to worry! Give us a call and we can go over various exhaust fan base size options with you.
So what upblast exhaust fan CFM is right for you?
The right CFM for your upblast roof ventilator is going to rely on your answers to the four questions above. If you provide a HoodFilters.com product expert with that information, we can work directly with the manufacturer to determine the exact specifications for a fan that will be the perfect addition to your ventilation system.
There are a few different ways to supply the information to us. You can call us at 877-394-9731, email us, or use our new online Hood and Fan Builder tool to help guide your vent hood CFM calculation for anything from a single upblast ventilator to a complete hood and fan ventilation system. As always, let us know if you have any questions or need any assistance with choosing products.
In this short video, learn how to quickly determine the right size upblast exhaust fan when buying a new exhaust fan or replacing an existing one in your commercial kitchen or restaurant.