Without proper ventilation, no kitchen can operate efficiently. Unfortunately, exhaust hoods are one of the biggest energy hogs in the kitchen. Let's look at some of the factors to consider when purchasing an exhaust hood.
The primary objective of the exhaust hood is to remove contaminated air from the area around cooking equipment. Effective removal requires a certain velocity of air movement called the capture velocity. This air curtain created by the proper air velocity will hinder smoke and heat spilling into the rest of the kitchen.
The secondary objective of the hood is to remove grease from the exhausted air prior to it entering the building's ductwork and exhaust fan. All exhaust hoods have a device for removing at least some small grease particles. The more expensive hoods have fixed baffles that cause air to whip around inside and throw out grease particles by centrifugal force. These are generally considered more efficient in removing grease. Less costly hoods use removable filters to capture grease particles. These filters are less efficient than most fixed baffles, although generally acceptable. The key is to consider the costs.
Low-end basic models can be purchased for about $500-$600 per foot of length, while some premium automatic-wash styles can be nearly three times that. Obviously, these costs add up quickly. A typical cooking arrangement of five appliances will require a 16- to 17-foot hood, a fire protection system, ductwork and an exhaust fan. The cost for the entire package will be $15,000 on the low side.
Some of the differences in costs relate to how effective the model is at extracting grease from the exhaust air stream, and how difficult it is to clean the unit or whether it cleans itself. Hoods engineered to remove less air while providing effective capture are generally more costly. Some owners are willing to pay the premium because it reduces their heating and air conditioning bills.
Hoods and fire protection systems contained within have more legal requirements than any other equipment in the kitchen. Typically, the health department is concerned about sanitation, while the fire and building departments are worried about fire hazards and environmental agencies are worried about the smoke emissions pouring from the ducts. In any case, there must be an automatic fire suppression system in hoods over most cooking equipment.
New requirements within the past few years call for more fire protection, so be prepared to change or enlarge your system to meet current regulations. Also be prepared to upgrade if you renovate or make equipment changes in the cooking lineup. A new fire suppression system can be costly, usually several thousand dollars, and perhaps cause some down time during installation.
One important consideration in hood operation is comfort of your customers. A properly engineered ventilation plan will call for more air being exhausted than is replaced in the kitchen. Negative pressure will help ensure that cooking odors don't escape into the dining room or other public spaces, which may be offensive to guests.
Hoods don't require mechanical maintenance since they have no moving parts. The key is to keep the unit clean on a daily basis. The more expensive hoods have water-wash features that employ a timed hot water and detergent spray wash of the hood interior. Water-wash hoods are initially more costly than a typical hood, but offer labor savings for some operations. When comparing costs, be sure there is a drain and adequate hot water supply for a water-wash hood. Detergent, which is automatically dispensed, also needs to be factored into the cost.
Removable filters in hoods should be cleaned daily. Cleaning intervals may be less for filters above non-grease- producing equipment, but do keep the filters and hood surfaces clean so grease doesn't build. Ductwork also requires regular maintenance. The nearly universally accepted National Fire Protection Association (NFPA) standard requires inspection of the fan and ductwork for grease buildup and fire hazards every six months by a qualified vent cleaning service.
Hood exhaust is measured in cubic feet per minute (cfm). Each cfm of air your hood is designed to extract, costs about $3 or more per year to heat and air-condition. So if you consider a high-efficiency hood that exhausts 3,000 cfm, and compare it to a traditional hood of the same length, you will save up to half the air quantity (1,500 cfm) or $4,500 or more a year. A high-efficiency hood costs more up front but may pay you back quickly. Do an analysis with the help of your local utility company to compare.
Another exhaust-air saver to consider is a variable speed fan control. In down times or when cooking is light, the control automatically reduces the air being exhausted, thereby saving you air conditioning costs. Some of these units monitor temperature in the hood and others also monitor smoke to sense the need for more or less exhaust. Many operations have shown paybacks of a year or less.
Hoods are often ignored as long as they are doing their job. Don't hesitate to use the service and advice of experts to help you make the best equipment selection or the most cost effective choices.
Dan Bendall is a principal of FoodStrategy, a Maryland-based consulting firm specializing in planning foodservice facilities. He is also a member of Foodservice Consultants Society International. Bendall can be reached at 301-926-8181.