Residential kitchen design requires a general understanding of ventilation and how it relates to the performance of kitchens we build and products we specify. It’s always wise to partner with an appliance specialist when specifying a ventilation product. Specifying kitchen ventilation begins by establishing a theme for the design and then incorporating a corresponding hood style. Ventilation design options include decorative wood hoods with stainless steel liners, chimney-style hoods that incorporate ventilation into a decorative design element and downdraft ventilation that can be built into a cooktop or range and added as a separate component.
Most commercial style/luxury manufacturers recommend the hood extend 3 inches beyond each side of the cooktop or range and at least have the same depth as the furthest burner off the wall. This means a 36-inch cooktop or range could require a 42-inch-wide hood that comes flush to the face of the furthest burner off the wall (21-inches deep). There also may be a requirement for the distance from the burner horizontally and vertically to a noncombustible surface.
The unit also needs to be sized. Fans or blowers are sized in CFMs, the amount of cubic feet of air their fan moves per minute. The simplest formula to establish what size is required for adequate ventilation is to allow 1 CFM of air flow for every 100 BTUs of heat output per appliance being considered for ventilation. A second way to determine the CFM requirement for the ventilation product is to allow for 15 changes of air per hour in the room that the appliance is being placed. The designer would take the entire volume of the room that the appliance is in (length times width times height). Cubic feet of the room multiplied by 15 exchanges per hour divided by 60 minutes equals total CFM.
Once the CFM requirements are determined, the designer has to determine a feasible route to vent or exhaust the odor and moisture outside. Sometimes, beautiful hoods are ordered and fabricated and at the point of install, the designer finds out there is no way to ventilate the hood through an outside wall or ceiling. The designer has to consider several things. If the blower is mounted on a wall, is there an opportunity to vent it directly through the wall? If not, can it be vented up and out or down and out? If the unit is being installed over an island or peninsula, can the ducting be routed through the ceiling/floor system? If not, can a decorative soffit be incorporated to make sure ductwork can be installed?
All fans remove or displace the existing air in the environment in which they are placed, which must be taken into consideration. If there is a chimney to a fireplace or gas appliance, when turned on, a large kitchen exhaust fan can suck the gases from the flues of these appliances back into the house The ventilation fan also can extinguish a pilot light on a furnace, stove or water heater. This phenomenon is called backdrafting. Gas accumulation from extinguished pilot lights and chimneys can cause asphyxiation and explosions. Whenever a designer specifies a large CFM ventilation product, he or she needs to consider how to provide makeup air into the room the blower is in. This can be as easy as making sure all of the doors in a house are undercut 1 inch or as complicated as installing a makeup air solution that turns on a home’s HVAC blower when the fan is activated on the ventilation product. It is best to consult with your building-code official or appliance specialist for solutions that will address legal solutions for makeup air.
It is important to understand the types of ventilation products available and what best suits your design and your customer’s taste. Rely on your experience and partner with a trained appliance specialist and local code official to ensure you are providing your clients with the safest and most efficient choices for their design.