Air Maximum

Proper ventilation takes proper planning
By Karen Collins
May 14, 2010

In a recent survey conducted by a leading appliance manufacturer in conjunction with the National Kitchen & Bath Association (NKBA), almost 90 percent of 573 kitchen designers said that their clients either “always” or “usually” rely on their professional opinions regarding a kitchen’s ventilation needs. In addition, 86 percent of the designers polled noted that client knowledge about kitchen ventilation appliances was considerably less than that of other appliances.

For some industry professionals, the responses are not that surprising. “Homeowners tell us that they rely heavily on their kitchen designer to help them select the proper ventilation they need not only for the cooking surface it interfaces with, but for their unique cooking style,” said Brian Wellnitz, marketing manager for kitchen ventilation at Broan-NuTone. “The technical aspect of kitchen ventilation knowledge is one of the many benefits a kitchen designer can bring to their client, increasing the value proposition of hiring a professional.”

Although kitchen ventilation style and technology will continue to evolve, the process by which proper, effective kitchen ventilation is achieved remains based on proper planning and the incorporation of the following steps.


•  Design it in. If you consider the ventilation first when designing a kitchen, the level of challenge drops dramatically regarding duct installation and application issues. In addition to providing ventilation at the cook source, consider adding it near wall ovens and over sinks and prep surfaces to help remove excess heat, steam and odors.

•  Consider current and future needs. Design for your client’s current and future requirements. Will access to controls be an issue? Will lighting requirements change? According to Wellnitz, homeowners, especially baby boomers, are requesting brighter, more even lighting that reduces shadows and “makes it easier to see instructions, measurements and pot/pan contents.”

•  Recognize that recirculation is not ventilation. Many hoods can operate in two ways. Ventilation removes airborne particles to the outdoors, and recirculation removes particles from the immediate cooking area while most of the vapors stay in the home. This in turn can diminish the indoor air quality (IAQ) and increase the damaging effects to surrounding surfaces. In fact, some cabinet manufacturers void their warranties if adequate cooktop ventilation is not provided.

•  Observe and address crosscurrents. Strong crosscurrents can affect a range hood’s ability to capture vapors and grease from cooking by pushing the heat plume outside the hood’s capture area, thus allowing the particles within the plume to land on surfaces, and odors to linger for longer periods of time. Windows and patio doors that are frequently opened are a prime source of crosscurrents; others include ceiling fans, forced heating registers or garage entry directly into the kitchen. Taking simple precautions, such as creating a two-tier counter with a raised portion, can prevent crosscurrents from moving across the cooking surface, thus reducing their effects.


•  Consider your installation options. If code and building regulations permit ventilating to the outdoors, determine possible termination points on the home’s exterior and work back to possible hood locations. Pinpoint the paths that offer the shortest runs with the fewest turns and note the size limitations for the duct. When it comes to duct size, bigger is always better!

•  Match the hood to the installation. Once duct size options are determined, consider only hoods that connect to that size duct without being constricted. Hoods with larger duct connections—those requiring larger ductwork than will fit the installation parameters—demand transitions that will constrict the air flow and should only be considered if reduced performance and higher sound levels are acceptable.

•  Simplify ductwork connection. Look for hood models that match the location ductwork. Some hoods only offer a duct connection out the top of the hood. Others offer greater flexibility by allowing duct attachment through the top or back of the hood, or even allow rectangular or round connections.


•  Determine the cooking equipment requirements. Use the manufacturers’ recommendations or the following formulas as a starting point to gauge cfm for wall hoods: 1) Under 60,000 Btu or for electric cooktops, estimate 100 cfm per ft. of cooktop width, or 2) over 60,000 Btu, estimate 1 cfm for each 100-Btu output of the cooktop.

•  Consider the user’s level of cooking usage. Are they the “warm the soup up” type or more “culinary extraordinaire”? The starting cfm level for the former could be reduced without having a negative impact, whereas the latter may need increased cfm to achieve operational satisfaction. Also keep in mind that the addition of a grill or griddle in a cooktop requires an addition of up to 200 cfm to the estimation.

•  Adjust for hood style and installation. A sleek hood may not have an internal blower that is large enough to produce the needed cfm. Some, however, offer a choice of external blowers for higher cfm, which can be attached to larger ductwork, thereby responding to both style and performance requirements. Island hoods require more cfm for the starting point, conventional cooktops need 150 cfm per ft. of cooktop width, and for high performance, add 100 cfm to the estimate based on 1 cfm per 100 Btu.

•  Consider quiet operation. To have the quietest operation possible, choose the model that affords you the highest cfm, even though it may be much more than required. This will also require appropriately larger ductwork. “The advantage comes not in the high speed but in the lower normal speeds where sound levels can be more than 50 percent quieter,” said Wellnitz. “Another option, external blowers, not only affords you the performance option, but they are the end-all in quiet operation.”

In addition, look for a range hood with a quiet operating rating at normal and mid-range, which will also ensure ventilation for 95 percent of consumer cooking. Select an HVI (Home Ventilating Institute)-rated hood for confidence in the ratings—the lower the Sone rating, the quieter the hood will be—and opt for multilevel controls to provide a choice of quiet operations at various low settings.


•  Determine the capture area. The “capture” area of the range hood is typically defined by the outermost perimeter of the hood bottom. At a minimum, the width of the hood should extend the width of the cooktop and the depth should cover 100 percent of the back burners and at least 50 percent of the front burners. Making the hood wider and deeper can promote greater performance, effectiveness and overall user satisfaction. Wellnitz added, “In some locations you may find that it is code to have the width of the hood be 6 in. greater than the cooking surface.” If adequate coverage is a challenge, however, maximize the situation by installing the hood at its lowest recommended height, selecting a model with at least a 4-in. sump and increasing the cfm by at least 100 cfm.

•  Understand “sump” importance. The “sump” is the inverted area of the hood bottom that acts like a sink to hold the inrush of heat and smoke from more extreme cooking or higher levels of heat until the blower can drain it away, thus preventing smoke from spilling over the edge. If possible, select designs that have at least a 1-in. sump. With high-Btu cooking, it is a good idea to increase the sump size. If the hood design has a minimal sump, consider increasing the cfm.

•  Maximize filter size. Filtration keeps more of the grease byproducts out of the hood and duct system and on surfaces that are more easily cleaned. Larger mesh filters provide greater capture and allow air to pass more slowly through the filters, making them more effective while reducing noise. Most filters are easy to remove and clean in the dishwasher.

•  Match filter to cooking style. Baffle filters are “excellent choices” for frequent grilling or frying, “but make sure the user knows that the unit needs to operate on high speed to get the best results,” said Wellnitz. By contrast, mesh filters filter regardless of the speed at which the hood is operating. Some of the newer filters combine both to offer “the best of both worlds,” said Wellnitz.


•  Follow manufacturer recommendations. Range hood manufacturers all have recommended ranges of installation height over the cooking surface. The lowest level is the absolute minimum because this is the distance at which the hood was safety-tested by UL or some other agency. Typically, the upper limit of the installation range is a recommendation that will still give you satisfactory capture.

If you fail to follow recommendations, an inspector may force the removal of the hood or, over time, it may experience failures related to excessive heat on components. Installing a hood at heights higher than recommended poses no risk to the product, but will reduce capture capacity, resulting in potential user dissatisfaction. Also, in some chimney hood situations, the upper installation limit may be set by the dimension limits of the flue.

•  Make adjustments when the hood is installed higher than recommended. Some situations do require, for the benefit of the user, that the hood be mounted higher than recommended. If so, consider adding 100 cfm for every 3 in. above the recommended height, selecting a hood that is 6 in. wider than the cooktop or, for optimum performance, doing both.


•  Select automatic features and the right controls. Automatic operation features that turn the unit on or off provide added convenience and overall increased IAQ. Make the range hood easy to use by selecting a model with easy-to-operate and accessible controls or even remote controls. Again, consider today’s use and future use.

•  Provide sufficient cooktop lighting. Because lighting is a feature that homeowners use every day, ensure bright illumination with adequate cooktop coverage, as well as a low setting for nighttime safety. Today, range hood lighting can be tied into a kitchen’s controls to provide a unified solution for ambient lighting.

With the Environmental Protection Agency (EPA) having identified the kitchen as the number one source of airborne contaminants in the home, selecting the right hood, as well as proper installation and usage, can go a long way in ensuring good indoor air quality. Wellnitz said, “Kitchen designers have an incredible opportunity to demonstrate not only their design talent, but also their technical expertise in providing homeowners with the kitchen ventilation they need, require and expect from the kitchen professional they trust.”

—Karen Collins, APR, is marketing communications manager for Broan-NuTone LLC.
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