Healthy Homes Need to Breathe
Designing your Kitchen – Ventilation
By William Martin, Certified Kitchen Designer®
Ventilation for your home may not seem like the exciting, sexy part of kitchen design, but without it your home would fill with smoke, grease and odors from cooking, excess humidity and allergens.
In the 1960s my family lived in a modest home where the kitchen had a basic twelve-inch Magic Chef exhaust fan located in an exterior wall. I remember on hot Minnesota summer days, the years of accumulated solidified grease in the fan would soften and lazily descend from the fan and down the wall. Kitchen ventilation has come a long way since then.
The kitchen is the most important area in the home to effectively ventilate. Today a wide variety of ventilation configurations and design options accommodate even the most challenging applications. Plan ventilation early in the kitchen design process.
There are two basic kitchen ventilation design systems to consider.
Re-circulating systems filter room air with varying degrees of success, depending on the design and filter quality, and return it to the same room. These systems are the most economical and, in some circumstances such as multiple-unit buildings, condominiums or remodeling projects where the room or the home's construction does not allow easy access to an outside wall, are the only option.
External exhaust systems are the most effective. Contaminated air is drawn through filters then directly exhausted to the outside of the building. External exhaust also provides the health benefit of removing carbon monoxide fumes produced by gas cooktops. External exhaust fans are sized by the volume of air they move, measured in Cubic Feet per Minute (CFM).
Serious cooks and those who grill, broil, deep-fry, etc., appreciate the efficiency of external exhaust systems which move a large volume of air. Typically, residential external systems are sized at 600, 1000, and 1400 CFM, although larger and smaller sizes are available.
Kitchen ventilation Types and Locations
The three locations for ventilation include hoods (canopies) above the cooking surface, downdraft integrated into the cooktop or range, and wall or ceiling exhaust fans venting directly to the outside of the building.
A ventilation system filters five different contaminants produced from cooking: heat, steam, odors, smoke and grease. All except grease are lighter than air.
Grease leaves the hot cooking surface lighter than air but quickly returns to a solid when cooled, settling back on the cooking surface, adjacent cabinets, shelves, walls and countertops. The farther the exhaust system is located from the cooktop, the less effective it is at capturing grease.
A ventilation hood located above the cooking surface is the most popular and effective at capturing lighter-than-air contaminants. Ventilation hoods are sized six inches wider than the cooktop below to more effectively capture lighter-than-air cooking contaminants which tend to expand outward as they rise from the cooking surface.
Hoods can create a focal point in the room and are a design opportunity. Manufacturers create hoods with decorative exteriors fabricated from a variety of metals and metal finishes with filter systems contained inside. Ventilation inserts (liners) are self-contained mechanical units incorporating a fan and filters enclosed within a decorative façade such as plaster and moldings built on site.
Exhaust hood features may include integrated task lighting to illuminate the cooking surface and heat lamps. Many offer filters that can be cleaned in the dishwasher. Off/on switches for lighting and fan speeds are usually located within easy reach on the hood.
Downdraft ventilation is an option for kitchens with an open feeling where a hood might be visually distracting or impractical. In some circumstances the construction of the building is more conducive to downward ducting through the floor.
Downdraft ventilation is not as effective as a hood because air is suctioned very close to the heat source. Smoke, steam, odors and heat all rise quickly and escape the suction of the downdraft fan. Conversely, the heat from the cooking element is captured and exhausted. Fumes from tall pots and burners located the farthest from downdraft ventilation are hardly affected by the suction of the exhaust. Downdraft systems, however, may be the most effective at capturing grease before it solidifies.
Both hood and downdraft systems may be installed as re-circulating or external exhaust. Fans for external exhaust systems may be located in the ventilation unit, in the duct work or on the outside of the building.
Wall and ceiling exhaust fans are a vestige of the past; however, occasionally I have encountered kitchen ventilation situations where an external exhausting ceiling fan was the best ventilation solution. There are a variety of fans and filter options available.
Healthy Homes
Homes built today are more tightly constructed than ever before minimizing air exchange between interior and outside air. In addition, owners are installing larger cooking surfaces and kitchen exhaust systems. If an external exhaust system is removing 600 CFM to the outside from your kitchen, where is that air coming from if not from the outside? If exhausted air is not replaced, the house will theoretically collapse from suction because negative pressure is created inside the home.
Homes should maintain positive pressure inside the structure. When a door or window is opened, air should flow out rather than in. From an economical standpoint, it is easier to heat or cool a small amount of air lost through opening a door or window than to heat or cool the whole room because negative pressure drew air in.
Supply Air
External exhaust systems perform best when combined with a supply air source. When the exhaust ventilation system is turned on, air from the outside is introduced to recover air exhausted. Opening a door or window is the simplest but the least practical. An intake fan is a better solution. Typically these are connected to the exhaust fan and introduce outside air into the home when the exhaust fan is turned on replacing contaminated air exhausted to the outside and maintaining positive (or neutral) air pressure in the home. Kitchen exhaust ventilation combined with supply air systems work efficiently and effortlessly and result in lower electricity use and better ventilation.
From a safety standpoint, negative air pressure caused by external exhaust systems with no provision for supply air may create a health hazard. When a window or door is opened near a gas furnace or water heater exhaust, air contaminated with carbon monoxide could be drawn in. Maintaining positive air pressure in a home will eliminate this potential hazard.
Whole House Ventilation
Recently I visited longtime friend and visionary Steamboat Springs architect Joe Robbins to explore his views on kitchen ventilation.
Joe's preference for kitchen ventilation is an external exhaust hood, with its focal point and design theme opportunities. Many of his kitchen designs use a ventilation hood insert with a decorative façade which he designs and the builders construct.
Robbins emphasizes the importance of supply air and identifies whole home ventilation or, more specifically, Heat Recovery Ventilation (HRV) systems as the best source. Joe's experience with whole house ventilation began about fifteen years ago. He confirms that as residential home construction techniques and materials improved, we created a new problem: homes that are so tight they don't breathe.
Tight buildings trap dirty interior air and provide little exchange with fresh outside air except through doors and windows. Buildings need to breathe; dirty air, excess humidity and allergens have to be expelled, and fresh clean air introduced for a healthful living atmosphere.
HRV units are usually installed at the highest part of the home, near or on the roof. Dirty interior air is exhausted from the home and outside air is drawn in through the HRV filtering system. Inside air exhausted through the HRV system transfers its temperature to the incoming outside air. Thus, the home's main heating and cooling system doesn't need to heat or cool new outside air drawn in resulting in a significant cost saving.
HRV systems can connect to all exhaust fans in the home (bathroom, utility, garage, kitchen, etc.) to compensate for any air exhausted and air pressure loss in the home. HRV systems are calibrated to detect room pressure and always maintain positive pressure. Additionally HRV systems can monitor and maintain desired humidity levels.
Today Robbins recommends HRVs for all new homes and most remodeling projects he designs. He emphasizes the advantages of an HRV system in the home far outweigh the initial cost.
Minnesota and California have mandated supply air systems when external exhaust systems are installed. We can expect more regional and local governments to address the issue of healthy environments in new home construction in the future.
You don't need to wait for a kitchen or home remodel to upgrade your kitchen ventilation. Recirculation systems are easily retrofitted by simply adding a hood over your cooktop or purchasing a new range with an integrated downdraft system. Depending on the location of your cooktop to an exterior wall, it may be relatively easy and cost effective to upgrade to an external exhaust. Supply air systems and whole home ventilation require ductwork in the walls and may be impractical to retrofit in an existing home but should be considered in all new home construction. With the ventilation options available today it is possible to create an energy efficient, clean, healthy and safe living environment.
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