A big expense, but kitchen exhaust systems are not the place to skimp.

Kitchen exhaust systems represent one of the bigger expenses in a professional kitchen and on an operator’s electricity bill. A well-designed system can help control utility costs and improve an operation’s environment. In contrast, a poor system can spike gas and electricity bills sand literally suck insects into a restaurant.

Most exhaust systems fall into two categories. Type one systems work with cooking equipment that produces grease-laden vapors, such as stoves, chargrills and flattops. These systems must have watertight welds throughout, including the ductwork that leads out of the building. Given the highly flammable nature of grease, restaurants must equip these systems with internal fire suppression systems.

Type two hoods work with equipment that doesn’t produce grease, but does generate heat and moisture, such as warewashers, convection ovens and steamers. These can hoods use  “s” ductwork that’s practically off the shelf and does not require need any fire suppression, making them less expensive than type one hoods.

While it’s easy for operators to know what type of hood they’ll need, the exact specification of these systems should be left to kitchen design professionals, typically sales engineers and the hood manufacturers, says Wayne Stoutner, president of upstate New York-based service agency Appliance Installation & Service. Based on the operation’s equipment lineup, these professionals will be able to determine the exact style of hood for the operation and how much air it should pull, measured in cubic feet per minute (CFM).

How much air the system extracts  sets the specifications for another key element of a well-designed kitchen exhaust system, the make-up air unit, which brings in air from outside to replace the expelled air. Make-up air units can come with optional heating and cooling modules that condition the air drawn from outside. Because exhaust systems are costly, operators regularly try to save money by not installing these modules.

In areas with extreme heat or (especially) cold, that is a mistake, says Stoutner.“In the last couple of years we’ve had several installations where people have decided not to have the heated module put on. Usually by mid-winter — not even the end of winter — They’re calling saying it’s freezing cold, please come add this module. The problem with that is that it’s much more expensive to do after the fact. It’s a whole other job at that point. For just a small installation it’s probably a couple of thousand dollars extra.”

A make-up air system should actually pull in slightly less air than the restaurant expels, , says Stoutner. Having slightly negative air pressure in the kitchen compared to the rest of the operation prevents cooking heat and smells from flowing to the dining area.

Design the make-up air system to work  with the HVAC system to draw slightly more air into the operation than goes out. This positive pressure to the outside helps prevent insects from entering the restaurant and keeps out air that hasn’t been cooled or heated.

Despite the importance of make-up air, it’s not uncommon to find operations with inadequate make-up air systems. The giveaway: The restaurant’s door is difficult to open due to the negative air pressure. While making it hard for customers to get in is bad, even worse is how this situation drives up energy bills.

Without a make-up air system, for example, a hood that pulls 2,000 CFM will completely empty the air out of a 2,000-square-foot operation with 10-foot ceilings in just 10 minutes. While that’s an extreme example, even a moderately undersized make-up air system can cause real problems.

“That air has to come from somewhere,” says Stoutner. “It’s going to get sucked in through the doors, the cracks in the windows. It’s going to remove all your heating and air conditioning. Then of course your HVAC can’t stay up because it’s running full bore.”

Downed HVAC systems, higher utility costs and expensive retrofits. All these can result from kitchen exhaust systems that have been poorly designed or overly “value engineered.” Operators should pay close attention to the system designs provided by professionals. In the long run, any changes could end up costing operators far more than they save.