Exhaust hoods help keep kitchens more comfortable by expelling air contaminated with heat, smoke, grease and cooking fumes. They also help keep kitchens safe with their integral fire suppression systems.
Exhaust hoods are also one of the biggest energy hogs in the kitchen because they pull out air that you spend a lot of money to heat or cool. It's estimated that about 75% of a restaurant's heating and cooling costs are sucked out through cooking exhaust hoods. If you can reduce the exhaust air and still remove smoke and fumes, you can save your operation a lot of cash. 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. Contaminated air can only be contained and removed well if an air curtain is created around the cooking equipment surface up to the point where air enters the hood. Effective removal requires a certain velocity of air movement called the capture velocity. This air curtain, created by proper air velocity, will hinder smoke and heat spilling out into the the kitchen. The critical part of removing contaminants is what happens down at the cooking surface, not how much air is moving up at the exhaust hood.
All exhaust hoods have a device for removing at least some small particles of grease from the air stream. The more expensive hoods have fixed baffles that cause air to whip around and throw out grease particles by centrifugal force. They are generally considered more efficient in removing grease. Less costly hoods use filters to help capture grease particles. These removable filters are less efficient, but acceptable for most applications. To get an idea of what is best for you, consider the costs.
Low-end basic hoods or ventilators can be purchased for about $500-600 per foot of length, while some premium automatic wash styles can be nearly three times that. As you can see these costs add up quickly. A typical cooking arrangement of five appliances will require a 16-17 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. Cost is also determined by the amount of air that must be exhausted by a given size hood to effectively remove smoke and odors. 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, the fire and building departments are concerned about fire hazards, the environmental agency is concerned about smoke emissions and insurance companies are concerned about the overall hazard to you property. In all cases there must be an automatic fire suppression system in hoods over most types of cooking equipment.
New requirements call for more fire protection than in older installations so be prepared to change or enlarge your system to meet current regulations. Also be prepared to make the system change everywhere if you renovate or make equipment changes in the cooking line up.
Hoods don't require mechanical maintenance since they have no moving parts. The maintenance required is keeping the units clean on a daily basis. More expensive hoods have water-wash features that do much of the cleaning for you with a timed hot water and detergent spray wash of the interior of the hood. Water-wash hoods that automatically clean themselves are labor savers. They are initially more costly than a typical hood, but may be worthwhile in ongoing labor savings for some operations.
When comparing costs make sure you have a drain and an adequate hot water supply. Detergent that is automatically dispensed also needs to be factored into the cost. Removable filters in hoods should be cleaned daily by removing the filters and scrubbing out the grease or washing in a dishwasher. 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 up and become a fire hazard. Ductwork requires regular maintenance also to prevent it from becoming a potential fire source. The National Fire Protection Association (NFPA) requires inspection of the fan and ductwork for grease build up and fire hazards every six months by a qualified vent-cleaning service.
Some hood manufacturers have introduced new super-efficient hoods to reduce air quantities to a minimum. An exhaust air saver to consider is one that reduces the overall air volume through a variable-speed fan control. These controls monitor the air entering the hood and sense when no or little cooking is going on. In down times or when cooking is light, the control automatically reduces the air being exhausted. Some of these units monitor temperature in the hood and others may also monitor smoke to sense the need for more or less exhaust. Many operations have shown paybacks of a year and even less for these systems.
One manufacturer has introduced hood filters with cold water lines that are preheated by passing the hot waste air from cooking over them to produce hot water for your kitchen. Hoods are often ignored as long as they are doing their job. It's often easy to forget how complex they are and especially how much of an investment you have in them. If you are in the market for a hood, check out the latest in energy saving models.
Dan Bendall is a principal of FoodStrategy, a Maryland-based consulting firm specializing in planning foodservice facilities. He can be reached at dbendall@foodstrategy.com.