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Nutone kitchen exhaust fan installation ca 1970 (C) Daniel Friedman Kitchen Ventilation Design Guide
Best Practices in the selection & installation of kitchen exhaust fans or kitchen vent systems

  • KITCHEN VENTILATION DESIGN - CONTENTS: design specifications & product recommendations for kitchen ventilation, & kitchen vent fan installation guidelines. Kitchen Range Hood Location Advice. Required Kitchen Fan Ventilation Rate. Installation Specifications for Kitchen Island Hoods. Downdraft Fans for Kitchens. Kitchen Vent Fan Noise Ratings & Advice. Backdrafting & Safety Issues with Exhaust Fans.
  • POST a QUESTION or READ FAQs about kitchen ventilation system design, installation, choices, and best practices, Q&A on venting microwave appliances.
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This article discusses kitchen vent fans:

Kitchen vent fan types, ventilation rate, installation specifications, and noise ratings. We also discuss downdraft fans and kitchen fan noise issues. Our page top photograph illustrates a high capacity vertical rise range hood in a New York home. This is the most-effective kitchen exhaust ventilation design, but attention to fire safety is required with this and all exhaust fan systems.



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Kitchen Ventilation Design Guide: how to choose & install a kitchen vent fan

Nutone kitchen exhaust fan installation ca 1970 (C) Daniel Friedman Kitchen exhaust fan vent outside terminatinon - Nutone (C) Daniel Friedman

Kitchens and bathrooms are key sources of indoor moisture and other pollutants. Kitchens produce particulates and atomized grease from cooking, and with a gas range, they also produce combustion by-products including nitrogen dioxide and carbon monoxide. (INDOOR AIR QUALITY IMPROVEMENT GUIDE).

Our photos illustrate a traditional through-wall kitchen exhaust vent fan installed ca 1970 [DF]. The outdoor termination for this kitchen exhaust fan requires occasional caulking, and periodically the entire fan assembly is removed and cleaned to remove accumulated grease.

A magnetically-attached cover is sometimes installed over traditional through-wall kitchen exhaust fans to avoid drafts or heat loss in cold weather.

Kitchen cooktops produce large amounts of water vapor, atomized grease, particulates, and cooking odors. In addition, gas cooktops produce combustion by-products, including carbon dioxide, nitrogen dioxide, nitrous oxide, and carbon monoxide (see BACKDRAFTING HEATING EQUIPMENT).

The most effective way to remove the moisture and contaminants from a cooktop is with an overhead range hood vented to the outdoors. Unvented range hoods offer no protection against moisture and combustion gases and provide only minimal protection against grease, smoke, and odors trapped by the filter.

This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. Photographs are by Daniel Friedman.

Kitchen Range Hood Location Advice

Figure 6-57: Kitchen range hood location drawing (C) J Wiley, S Bliss

Research at the University of Minnesota has shown that many range hoods are too small, too high, or not oriented properly to do their job well. According to the study, the most effective range hoods are at least as wide as the cooktop and rectangular rather than angled in front.

For best performance, standard hoods should be mounted no more than 24 inches above the cooking surface and project out at least 20 inches from the wall (see Figure 6-57).

Figure 6-57

[Click any image or table to see an enlarged version with additional detail, commentary & source citation.]

Some high-capacity ventilators are designed to work from 24 to 30 inches above the cooking surface, but the stronger fans increase the risk of backdrafting other combustion appliances. Hoods integrated with microwaves typically project out only 13 to 15 inches and miss most of the contaminants generated by the front burners.

Required Kitchen Fan Ventilation Rate

The minimum ventilation rate for kitchens required by the 2003 International Residential Code is 100 cfm intermittent or 25 cfm continuous (if part of a whole-house ventilation system).

Table 6-14: Recommended ventilation rates for overhead kitchen range hoods (C) J Wiley, S Bliss

Most industry experts recommend that overhead range hoods have a minimum capacity of 150 cfm and recommend higher capacity fans for open grilling, high-BTU commercial-style ranges, and other cooking styles that generate greater than average steam or smoke (see Table 6-14).

Table 6-14

[Click any image or table to see an enlarged version with additional detail, commentary & source citation.]

A rule of thumb for high-output ranges is 1 cfm of ventilation per 100 BTU’s of output. With high-powered fans, multi speed controls are best so the fan speed (and noise) can be lowered when full power is not required.

Installation Specifications for Kitchen Island Hoods

Kitchen exhaust fan vent outside terminatinon - through attic, asbestos fabric (C) Daniel Friedman

Island hoods are typically installed at least 27 inches above the cook surface so they do not interfere with sight lines.

Because they are farther from the cooktop and subject to passing air currents, they require more powerful fans than standard wall-mounted hoods.

HVI recommendations for wall-mounted and island hoods are shown in Table 6-14 above.

Updraft Kitchen Exhaust Fan Fire Hazards

As Mr. Bliss noted above,

The most effective way to remove the moisture and contaminants from a cooktop is with an overhead range hood vented to the outdoors.

The interesting kitchen vent fan exhaust system shown at left was installed (we estimate) in this New York home in the 1930's. A combination of wood and metal site-built ductwork runs horizontally across an attic floor to a high-capacity exhaust fan located in the attic (green). The attic-mounted fan connects to a vertical roof exhaust port using asbestos fabric to avoid vibration damage problems.

I [DJF] was more concerned about the possible fire hazards in this long-in-place ductwork combined with a high capacity attic fan than with any possible asbestos worry. Grease accumulating in a cool horizontal kitchen exhaust fan duct is a fire hazard, as might be a fan in this location without any fire detection control or shut-off device. Just sayin' ...

Downdraft Fans for Kitchens

Because they lack a canopy to catch contaminants and must overcome natural convection, downdraft fans are less effective than overhead range hoods. Typically sized at 400 to 600 cfm or more, they do a reasonable job of venting barbecues and grills, but are less effective with pots and pans taller than about 3 inches.

Downdraft fans are either flush-mounted at counter level or pop up about 8 inches at the back of the range.

Kitchen Vent Fan Noise Ratings & Advice

Look for the unit with the lowest noise rating that meets the ventilation requirements. Some hoods are rated as low as 2.5 sones, although most range from 4 to 7 sones at full power (one sone roughly equals the sound of one quiet refrigerator).

Ductwork Suggestions for Kitchen Fans

Figure 6-4x: (C) J Wiley, S Bliss

Like bathroom fans, the airflow from kitchen exhaust fans is generally rated at a static pressure of 0.1 in. (see “Ductwork,” page 262).

This is roughly equivalent to 30 feet of smooth 7-inch round or 3 1/4x10 in. metal duct venting a 200 cfm fan.

For good performance, the total equivalent duct length, not counting the wall or roof cap, should not exceed about 30 feet. Equivalent duct lengths for common fittings are shown in Table 6-15.

[Click any image or table to see an enlarged version with additional detail, commentary & source citation.]

Backdrafting & Safety Issues with Exhaust Fans

With large-capacity exhaust fans of 200 cfm or greater, there is a risk of causing backdrafting of a fireplace or atmospherically vented boiler, furnace, or water heater.

The potential for backdrafting can be tested by a heating system technician and should be conducted with all household exhaust fans running to simulate the worst-case scenario. A simple preliminary test can be done by holding a stick of incense next to the draft diverter or dilution port of each combustion appliance with the furnace fan on and off.

If the smoke spills into the room for more than 30 seconds, then dedicated makeup air is most likely required. Modest amounts of makeup air can be delivered through a passive duct with an automatic damper, but significant depressurization may require an active supply fan.

The makeup air supply should be delivered into the kitchen or a nearby room not blocked by a door. (For more information see BACKDRAFTING HEATING EQUIPMENT.)

This article series discusses current best design practices for kitchens and bathrooms, including layout, clearances, work space, and accessible kitchen and bathroom layout, clearances, turning space, grab bars, controls, etc. We include advice on choosing and installing kitchen countertops, cabinets, and kitchen or bathroom flooring, sinks, and other plumbing fixtures and fixture controls such as faucets. A list of kitchen and bath product manufactures and sources is included just below.

Also see MICROWAVE OVEN VENT INSTALL

Reader Question: do we really need kitchen venilation at all?

(Mar 13, 2014) Jim said:
If downdraft fans are not that effective -- and a hood over an island takes up a bunch of space -- why not just skip the ventilation completely?

Is ventilation required in a kitchen?

Reply:

Jim,
There are two separate questions: the desirability of ventilation + code requirements for it and the energy efficiency & design requirements for ventilation.

For the former, national model codes and state, provincial or local codes indeed require kitchen ventilation, though "exhaust" and "ventilation" are mingled and sometimes a bit confounded. Here is an excerpt from M.D. Ewert's discussion of the Oregon building code on kitchen ventilation:

The requirements for ventilation in the ORSC can be found in Section R303.2, which states that
all habitable rooms are to be provided with an aggregate glazing area of 8 percent of the floor area, with a
minimal openable area of 4 percent of the floor area being ventilated. The purpose of the glazing and the portion that is openable is to provide both natural light and natural ventilation. Since a kitchen is considered a habitable room, it would require (at a minimum) a window, door, or other openings which opens directly to the outdoors, with an aggregate opening of at least 4% of the floor area. Sect ion R303.2 also allows the use of adjoining rooms to be used when determining this ventilation requirement

For the latter, ANSI/ASHRAE/IES Standard 90.1-2010 sets energy efficiency requirements for kitchen exhaust hoods and is discussed by a US DOE article on kitchen ventilation - www.energycodes.gov

Kitchen Exhaust Fan Companies

-- Adapted with permission from Best Practices Guide to Residential Construction.

Indoor Venting Articles

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