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Exhaust hoods are a necessary and crucial part of any commercial kitchen with open ranges, griddles, steamers, fryers, and other burners. Exhaust hoods capture and remove “bad air” – that is to say, they remove unwanted grease, smoke, steam, particulate matter, and dirty, odorous fumes from the air. Thus, in nearly every commercial kitchen, proper implementation of exhaust hoods is important for safety, efficiency, food quality, and quality-of-life purposes. Without a proper exhaust hood system, greasy air or smoke can set off fire alarms, interrupting the kitchen, and food residue in the air can stagnate, causing odor and flavor issues, as well as clogging up air ducts.
When making an exhaust hood purchase, you’ll have to take into consideration several different factors, including but not limited to: filter material, filter design and size, the type of exhaust hood and whether it is suitable to capture and filter the specific particulate matter created by your other appliances, whether the exhaust hood meets federal and state fire code requirements, how you will be removing the polluted air from your kitchen and whether the process will meet federal, state, and local code requirements, initial costs, and maintenance costs.
Exhaust Hood Filters
There are two main types of hoods – I and II – and each are designed to handle different particulate matter in the air. Your choice will depend entirely on what sort of particular matter you expect your equipment to produce.
Type I hoods are made to handle greasy, smoke-filled air, and, as such, the filter material and design for type I hoods should be of higher quality and efficiency (due to the health and safety implications of stagnant grease and smoke in the air – for example, grease buildup can increase the risk of fire in a facility). It is illegal under current regulations to use aluminum mesh-like filters in type I hoods.
Type II hoods are made to handle a less ‘difficult’ task, specifically, the excess heat and moisture produced by certain kitchen equipment. Many commercial kitchens opt for cheaper, less efficient filter materials and designs for their type II hoods.
There are many types of filter material in use out there, and some suppliers offer their own exotic selection – some may offer carbon fiber, for example – but the two primary materials in use in commercial kitchens today are aluminum and stainless steel.
Stainless steel material is, of course, substantially more expensive than aluminum, as is the case with nearly every other piece of restaurant equipment, but the advantages are many. In general, stainless steel constructions are more durable, easier to wash (they are dishwasher-safe, for example), are built stronger, require cleaning less frequently, and last longer. Typically, they are also more efficient.
Aluminum constructions are chosen almost entirely for cost reasons, but that does not necessarily mean that an aluminum filter will be unsatisfactory for your kitchen. It is important to consider your kitchen’s specific demands. For high volume kitchens, a stainless steel construction may be necessary because the efficiency and durability of the filter cannot be compromised. On the other hand, for low volume kitchens (kitchens that may be open for a shorter period of time during the day, for example) an aluminum construction may be perfectly adequate. Speak with your supplier to learn more about their material offerings – they may have a particular material construction that fits your needs more precisely.
Filters come in several styles – cartridge, mesh, baffle, centrifugal, and multi-stage. Baffle filters are the most common and, one of the most affordable filters, but they are also one of the least efficient of the filters.
filters are the least efficient and have fallen greatly out of favor in the commercial restaurant industry. In many cases, they have been banned from use for grease/smoke removal. Visually, they look like window meshes, though they are designed to catch kitchen-produced particulate matter and dust.
filters have a series of ridges laid flat next to each other. The ridges capture grease, smoke, moisture, and other particulate matter, which then slides down the ridges and into collection trays. There are a great variety of sub-types available even for baffle filters, some with handles to make it easier to install/remove, some with a hook system for easier installation and removal, and others with ‘spark arrestors’ which are specifically designed to eliminate free sparks that emit from certain types of restaurant equipment and materials.
filters have an in-between efficiency/cost result. They spin dirty air through the filter, using the force generated to push particulate matter out of the airstream, thus cleaning the air.
filters combine two or more filters to provide a second layer of support. For example, a multistage filter might combine a centrifugal filter and a mesh filter to catch any particulate matter that may have escaped only one filter.
filters are fast becoming more popular for light duty grease and smoke issues. They are some of the most efficient filters available on the market for those purposes, and in many tests they are shown to be more efficient than standard baffle filters. This efficiency comes at a cost, of course, as cartridge filters are typically more expensive than baffle filters, but there are other advantages to balance out the cost. Increased efficiency means that the fan life is improved, and in many cases cartridge filters can also be fitted to existing hood configurations. This means that cartridge filters make great candidates for upgrading an older kitchen’s air quality.
Since exhaust fan systems remove dirty air from the kitchen, you’ll have to introduce new, clean air back into the kitchen. Make-up air fans bring clean air supply back into the kitchen, but you’ll have to take several things into consideration before bringing new air into the kitchen. First, new air should be filtered too. Second, new air may need to be cooled or heated depending on the existing temperature environment of the kitchen (for example, the new air may need to be cooled if the kitchen is being air conditioned).
Maintenance and Pollution Removal
Exhaust air can create difficulties for commercial kitchens even after it has left the kitchen, because the polluted air may be expelled into the air inlets of nearby apartments, businesses, or streets, and there may therefore be complaints about smelly, polluted exhaust air expelled by the kitchen. To avoid this, many kitchens simply direct the exhaust air away from any nearby inlets, and many do it with a high velocity burst of air that shoots the exhaust air through a roof fan, but if that doesn’t solve the problem (or if there is no easy way to direct the exhaust air away from various inlets), some kitchens utilize a dilution method. Exhaust air dilution works by blasting fresh air into the exhaust air stream to ‘dilute’ the exhaust air and therefore to mask the smell/visuals of it.
Maintenance of an exhaust hood requires regular swipe cleaning, but also duct cleaning (especially if there are leaks), and filter cleaning. Stainless steel filters are dishwasher-safe, but most filters can be simply placed in a tub of soapy water and degreaser and sprayed with a hose.