Kitchen Exhaust

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Description

Regardless of what kind of ventilation system you have for the rest of the house, an exhaust fan should be installed in the kitchen to exhaust moisture and odors associated with cooking. The exhaust fan is typically mounted in a range hood or cabinet or on the wall over the kitchen stove. The fan should be ducted to exhaust outside of the home, not into the attic.

Recirculating fans that draw air through a filter and discharge it back into the room are not acceptable. Operable windows are a nice feature but they should not be relied on for consistent ventilation.

To fulfill the local exhaust airflow requirements of ASHRAE 62.2, kitchen fans can be run intermittently (occupant controlled) or continuously. Kitchen fans operated intermittently should have a flow rate of 100 cfm or more and continuous fans should have a flow rate of 25 cfm. If the fan is set to run continuously and the flow rate is less than 400 cfm, the sound rating must be no more than 3 sones. Exhaust fans operating in excess of 400 cfm must be provided with makeup air systems that will automatically start and operate simultaneously with the exhaust system and will provide makeup air at a rate equivalent to the exhaust. ENERGY STAR-rated exhaust fans should be selected that have low sone ratings, low power draw, and in some cases multiple speeds for spot exhaust and continuous ventilation.

Although a single-point exhaust fan such as a kitchen fan could be used to provide code-required whole-house ventilation, this strategy is not recommended. For more on whole house ventilation strategies, see Supply-Only Ventilation, Exhaust-Only Ventilation, Semi-Balanced Ventilation, and Balanced Ventilation – HRVS and ERVs.

Kitchen exhaust fans may be installed by the HVAC vendor or installer or by the kitchen range vendor if it is part of that system. This task should be included in the contract for the appropriate trade depending on the workflow at specific job sites.

How to Install Exhaust Fans

  1. Determine the appropriate fan size for your application. For a continuous rate of >= 5 ACH, ENERGY STAR recommends selecting a fan that provides more than 5 ACH in order to pull the required amount of air. For an intermittent rate of >= 100 cfm, ENERGY STAR recommends selecting a fan with a rating of 150 to200 cfm. Choose ENERGY STAR-rated fans for energy efficiency and low noise level.

Proper sizing of kitchen exhaust fan  Reference

2.  Install the fan either in the range hood, the cabinet above the stove, or on the wall above the stove. Follow the manufacturer’s instructions. The fan may also be integrated into a microwave oven mounted into a cabinet above the stove. Cut openings in the ceiling for the fan or exhaust duct no wider than needed to fit the fan or duct and air seal the opening with caulk or spray foam. Connect the exhaust duct to the fan box with mechanical fasteners, metal tape, and/or mastic, not regular cloth-backed duct tape.

3. Vent the kitchen fan exhaust directly to the outside, not into an attic, crawlspace, or space between floors. The duct should be smooth and straight with as few bends as possible. Use the diameter specified with the fan’s installation instructions; small diameter ducts could trap grease, creating a fire hazard. The duct should be made of metal and any seams should be sealed with mastic or metal tape. It should be routed so that it is out of the way of other ducts or equipment in the attic and care should be taken not to dent or crush the duct during or after installation.

4.  Locate the exhaust duct outlet vent on the exterior of the home at least 10 feet from any air inlet. The outside termination should be covered with louvers, a screen, or grills. The exhaust air should not be directed onto a walkway. The range hood duct should have a smooth interior finish, be airtight, and be equipped with a backdraft damper (2009 IRC M1503). If the fan is integrated with a microwave oven installed over the stove, install it according to the manufacturers’ instructions and 2009 IRC Section M1504.1. Exhaust hoods installed over domestic open-top broiler units should be installed with a minimum clearance above the cook top of 24 inches, and the hood should extend the full width and depth of the cooktop and follow other requirements of 2009 IRC M1505.1.


5. Visually inspect the fan and duct installation and test the fan for operation flow rate.

Ensuring Success

Visually inspect and test the kitchen exhaust fan for proper installation as follows:

  • Ensure that the fan exhausts outside, not into the attic; that it is set to exhaust, not recirculate; that any dampers on the outside termination are able to open freely; and that packing tape is removed.
  • Confirm that any openings cut in the ceiling for the fan or exhaust duct are properly air sealed and that the exhaust duct is sealed to the fan with both mechanical fasteners and mastic for a flex duct or caulk or spray foam for a rigid duct.
  • Check the sone rating; ASHRAE 62.2-2007 requires 3 sones or less for intermittent (occupant-controlled) kitchen or bath exhaust fans or 1.0 sone or less for continuous fans.
  • See the “compliance” tab for calculating exhaust rates to meet ASHRAE 62.2 requirements and ENERGY STAR guidelines for intermittent and continuous operation, as well as IRC requirements on fan size and openable windows. If the kitchen fan will be used as the primary means for meeting the code-required ventilation, calculate the ventilation rate required based on the size of the home, and ensure that the fan’s tested flow rate will meet this requirement.
  • Test the fan’s operation to determine the flow rate using a flow hood, flow grid, anemometer (in accordance with AABC, NEBB, or ASHRAE procedures), or other equivalent method. Kitchen fans are typically rated by how many cubic feet per minutethe fan will exhaust in a factory setting. Duct work, termination choices, and installation may decrease the measured cubic feet per minute below the factory-rated value. To ensure the installed fan exhausts the required amount of cubic feet per minute, EPA recommends the HVAC contractor install a fan with a rating higher than the required measured amount.

Scope

Kitchen exhausts directly to the outdoors at ≥ 5 ACH, based on kitchen volume continuous rate or ≥ 100 CFM intermittent rate

Local Mechanical Exhaust

In each kitchen, a system shall be installed that exhausts directly to the outdoors and meets one of the following Rater-measured airflow standards: *

Continuous rate is >= 5 ACH, based on kitchen volume.

  1. ENERGY STAR recommends selecting a fan that provides more than 5 air changes per hour (ACH) in order to pull the required amount.

Intermittent rate is >= 100 CFM and, if not integrated with range, also >= 5 ACH based on kitchen volume.

  1. ENERGY STAR recommends selecting a fan with a rating of 150 to 200 CFM to pull at least 100 CFM when measured.

Continuous and Intermittent

  1. Install the fan to directly exhaust to the outdoors through a termination with little or no restriction.
  2. Seal all seams, gaps, holes, and connections to the exterior of all ventilation ducts, preferably with mastic.
  3. ENERGY STAR recommends testing the kitchen fan after completing a visual inspection of proper duct sealing.

* All kitchen fans must comply with either the continuous of intermittent rate.

ENERGY STAR Notes:

The whole-house ventilation air flow and local exhaust air flows shall be measured by the Rater using a flow hood, flow grid, anemometer (in accordance with AABC, NEBB, or ASHRAE procedures), or substantially equivalent method.

Per ASHRAE 62.2-2010, an exhaust system is one or more fans that remove air from the building, causing outdoor air to enter by ventilation inlets or normal leakage paths through the building envelope. Examples include bath exhaust fans, range hoods, and clothes dryers.

Per ASHRAE 62.2-2010, a bathroom is any room containing a bathtub, shower, spa, or similar source of moisture.

An intermittent mechanical exhaust system, where provided, shall be designed to operate as needed by the occupant. Control devices shall not impede occupant control in intermittent systems.

Kitchen volume shall be determined by drawing the smallest possible rectangle on the floor plan that encompasses all cabinets, pantries, islands, and peninsulas and multiplying by the average ceiling height for this area. Cabinet volume shall be included in the kitchen volume calculation.

For homes permitted through 01/01/2014: Homes are permitted to be certified without enforcement of this Item to provide partners with additional time to integrate this feature into their homes.

For homes permitted on or after 01/01/2014: Homes shall meet this Item. Alternatively, the prescriptive duct sizing requirements in Table 5.3 of ASHRAE 62.2-2010 are permitted to be used for kitchen exhaust fans based upon the rated airflow of the fan at 0.25 IWC. If the rated airflow is unknown, >= 6 in. smooth duct shall be used, with a rectangular to round duct transition as needed. Guidance to assist partners with these alternatives is available from ENERGY STAR. As an alternative to Item 8.1, homes that are PHIUS+ certified are permitted to use a continuous kitchen exhaust rate of 25 CFM per 2009 IRC Table M1507.3.

All intermittent kitchen exhaust fans must be capable of exhausting at least 100 CFM. In addition, if the fan is not part of a vented range hood or appliance-range hood combination (i.e., if the fan is not integrated iwth the range), then it must also be capable of exhausting >= 5 ACH, based on the kitchen volume. Also, for intermittent kitchen exhaust fans that are itnegrated with microwaves, a rated air flow rate >= 200 CFM may be used in lieu of measuring the actual air flow rate.

Kitchen Fan Rating

Kitchen fans are typically rated by how many cubic feet per minute (CFM) the fan will exhaust in a factory setting. Duct work, termination choices, and installation may decrease the measured CFM below the factory-rated CFM.

To ensure the installed fan exhausts the correct amount of CFM, ENERGY STAR recommends the HVAC Contractor to install a fan with a rating higher than the required measured amount.

Additional Information

For additional information and specific duct testing protocols please refer to RESNET Chapter 8 (Standard for Performance Testing and Work Scope: Enclosure and Air Distribution Leakage Testing).

Kitchen Fan Selection

To calculate the CFM requirement of the kitchen fan for continuous rate, use the equation below:

Required CFM = (5 ACH) * (Kitchen Volume) / (60 minutes)

If intermittent fan flow rate of at least 100 CFM is less than 5 ACH, based on kitchen volume, then a vented range hood is required.

Kitchen Fan Testing Tips

  • Test the kitchen fan after completing a visual inspection of proper fan installation.
  • Verify the kitchen fan is set to “exhaust” instead of “recirculate.”
  • Use a flow hood, flow grid, anemometer (in accordance with AABC, NEBB, or ASHRAE procedures), or other equivalent method to test the fan.

Training

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Presentations

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Compliance

ENERGY STAR Version 3, (Rev. 07)

HVAC System Quality Installation Rater Checklist. The whole-house ventilation air flow and local exhaust air flows shall be measured by the Rater using a flow hood, flow grid, anemometer (in accordance with AABC, NEBB, or ASHRAE procedures), or substantially equivalent method. Per ASHRAE 62.2-2010, an exhaust system is one or more fans that remove air from the building, causing outdoor air to enter by ventilation inlets or normal leakage paths through the building envelope. Examples include bath exhaust fans, range hoods, and clothes dryers. Per ASHRAE 62.2-2010, a bathroom is any room containing a bathtub, shower, spa, or similar source of moisture. An intermittent mechanical exhaust system, where provided, shall be designed to operate as needed by the occupant. Control devices shall not impede occupant control in intermittent systems. Kitchen volume shall be determined by drawing the smallest possible rectangle on the floor plan that encompasses all cabinets, pantries, islands, and peninsulas and multiplying by the average ceiling height for this area. Cabinet volume shall be included in the kitchen volume calculation.

For homes permitted through 01/01/2014: Homes are permitted to be certified without enforcement of this Item to provide partners with additional time to integrate this feature into their homes.

For homes permitted on or after 01/01/2014: Homes shall meet this Item. Alternatively, the prescriptive duct sizing requirements in Table 5.3 of ASHRAE 62.2-2010 are permitted to be used for kitchen exhaust fans based upon the rated airflow of the fan at 0.25 IWC. If the rated airflow is unknown, >= 6 in. smooth duct shall be used, with a rectangular to round duct transition as needed. Guidance to assist partners with these alternatives is available from ENERGY STAR. As an alternative to Item 8.1, homes that are PHIUS+ certified are permitted to use a continuous kitchen exhaust rate of 25 CFM per 2009 IRC Table M1507.3.

All intermittent kitchen exhaust fans must be capable of exhausting at least 100 CFM. In addition, if the fan is not part of a vented range hood or appliance-range hood combination (i.e., if the fan is not integrated iwth the range), then it must also be capable of exhausting >= 5 ACH, based on the kitchen volume. Also, for intermittent kitchen exhaust fans that are itnegrated with microwaves, a rated air flow rate >= 200 CFM may be used in lieu of measuring the actual air flow rate.

DOE Challenge Home

Exhibit 1: Mandatory Requirements. Certified under ENERGY STAR Qualified Homes Version 3. EPA Indoor airPLUS Verification Checklist.

American Society of Heating, Air-Conditioning and Refrigeration Engineers (ASHRAE)

ASHRAE Standard 62.2-2010 Ventilation for Acceptable Indoor Air Quality in Low-Rise Residential Buildings for purchase by following the link above. The standard provides minimum requirements for mechanical and natural ventilation systems and the building envelope intended to provide acceptable indoor air quality in low-rise residential buildings.

2009 IECC

Section 403.5 Mechanical ventilation (Mandatory). Automatic or gravity dampers are installed on all outdoor air intakes and exhausts.

2009 IRC

Section M1507.3 Ventilation rate. Kitchens to have an exhaust rate of 100 cfm intermittent or 25 cfm continuous.*

2012 IECC

Table R403.5.1 Mechanical Ventilation System Fan Efficacy. Ventilation fans satisfy the following efficacy criteria*:
•    Range hoods and in-line fan: 2.8 cfm/watt.

2012 IRC

Section M1507.4 Local exhaust rates. Kitchens to have an exhaust rate of 100 cfm intermittent or 25 cfm continuous.*

 

* Due to Copyright restrictions, exact code text is not provided. For specific code text, refer to the applicable code.

More Info.

Case Studies

  1. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: September 2010

    Case study about new home construction in the hot-humid climate, part of a project building 100 new homes after hurricane Katrina.

References and Resources*

  1. Author(s): ASHRAE
    Organization(s): ASHRAE
    Publication Date: January 2013

    Standard defining the roles of and minimum requirements for mechanical and natural ventilation systems and the building envelope intended to provide acceptable indoor air quality in low-rise residential buildings.

  2. Author(s): DOE
    Organization(s): DOE
    Publication Date: June 2013

    Standard requirements for DOE's Challenge Home national program certification.

  3. Author(s): EPA
    Organization(s): EPA
    Publication Date: June 2013

    Standard document containing the rater checklists and national program requirements for ENERGY STAR Certified Homes, Version 3 (Rev. 7).

Last Updated: 08/15/2013

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