Intermittent Supply/Exhaust Fan Ratings
Scope
ENERGY STAR Certified Homes (Version 3.0, Revision 08) requires that exhaust fans used intermittently to meet code-required ventilation levels must have a sound rating of ≤ 3 sones as rated by the manufacturer.
- ENERGY STAR exempts the following from this ≤ 3 sone requirement:
- HVAC air handler fans
- fans with a rated flow of ≥ 400 CFM
- fans that are remotely mounted, i.e., fan located outside of the living space (e.g., in the attic) with 4 feet of ductwork between the fan and the intake grill, and with the Fans that are set for continuous operation to meet code-required ventilation levels must have a manufacturer-rated sound rating of ≤ 1 sone.
See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.
Description
Exhaust fans are often installed in bathrooms, kitchens, and laundry rooms to provide intermittent, localized ventilation. Fans that are overly noisy are more likely to be turned off quickly, perhaps too quickly to work effectively, for example to remove all the moisture in the bathroom after a shower or in the kitchen after boiling water. To improve indoor air quality and moisture control, quiet fans should be specified and installed. Fan noise is measured in sones; the lower the sone, the quieter the fan. Exhaust or supply fans installed for intermittent use should have a sone rating of 3 or less. For comparison, a quiet refrigerator operates at about 1.0 sones.
Fans exempted from this requirement include fans with a rated flow rate equal to or greater than 400 CFM, HVAC air handlers, and remote-mounted fans. To be considered exempt, a remote-mounted fan must be mounted outside the habitable spaces, including bathrooms and hallways, and there must be at least 4 feet of ductwork between the fan and intake grille.
For more on exhaust fan ratings, see Continuous Supply/Exhaust Fan Ratings and Bathroom Fan Ratings.
How to Select Low-Sone Supply and Exhaust Fans
- When specifying and purchasing exhaust or supply fans that will be used intermittently for local exhaust within the home, select quiet fans with a sone rating of 3.0 or less. The sone rating should be listed on the product label or in the manufacturer’s literature.
Figure 1 - The manufacturer’s label found on this exhaust fan housing shows a sone rating of 2.5. 
Ensuring Success
In homes where a fan is installed to provide intermittent supply or exhaust, the HERS rater should inspect to ensure that the fan’s noise level is rated at less than or equal to 3.0 sones by the manufacturer (not required on fans with flow rates equal to or greater than 400 cubic feet per minute).
Climate
No climate specific information applies.
Training
CAD Images
None Available
Compliance
ENERGY STAR Certified Homes (Version 3/3.1, Revision 08), Rater Field Checklist
7. Whole-House Mechanical Ventilation System
7.4 System fan rated ≤ 3 sones if intermittent and ≤ 1 sone if continuous, or exempted.43
8. Local Mechanical Exhaust - In each kitchen and bathroom, a system is installed that exhausts directly to the outdoors and meets one of the following Rater-measured airflow and manufacturer-rated sound level standards:42, 47
8.1 Kitchen Airflow at Intermittent Rate:48 ≥ 100 CFM and, if not integrated with range, also ≥ 5 ACH based on kitchen volume49, 50, 51
8.1 Kitchen Sound at Recommended Intermittent Ratee:48 ≤ 3 sones
8.2 Bathroom Airflow at Intermittent Rate:48 ≥ 50 CFM
8.2 Bathroom Sound at Recommended Intermittent Rate:48 ≤ 3 sones
Footnotes:
(42) The whole-house ventilation air flow and local exhaust air flows shall be measured by the Rater using RESNET Standard 380 upon publication and, in the interim, a flow hood, flow grid, anemometer, or substantially equivalent method.
(43) Whole-house mechanical ventilation fans shall be rated for sound at no less than the airflow rate in Item 2.3 of the HVAC Design Report. Fans exempted from this requirement include HVAC air handler fans, remote-mounted fans, and intermittent fans rated ≥ 400 CFM. To be considered for this exemption, a remote-mounted fan must be mounted outside the habitable spaces, bathrooms, toilets, and hallways and there shall be ≥ 4 ft. ductwork between the fan and intake grill. Per ASHRAE 62.2-2010, habitable spaces are intended for continual humanoccupancy; such space generally includes areas used for living, sleeping, dining, and cooking but does not generally include bathrooms, toilets, hallways, storage areas, closets, or utility rooms.
(47) Continuous bathroom local mechanical exhaust fans shall be rated for sound at no less than the airflow rate in Item 8.2. Intermittent bathroom and both intermittent and continuous kitchen local mechanical exhaust fans are recommended, but not required, to be rated for sound at no less than the airflow rate in Items 8.1 and 8.2. 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 (e.g., bath exhaust fans, range hoods, clothes dryers). Per ASHRAE 62.2-2010, a bathroom is any room containing a bathtub, shower, spa, or similar source of moisture.
(48) 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.
(49) 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.
(50) 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 at energystar.gov/newhomesresources. 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.
(51) 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 with the range), then it must also be capable of exhausting ≥ 5 ACH, based on the kitchen volume.
ENERGY STAR Revision 08 requirements are required for homes permitted starting 07/01/2016.
Exhibit 1: Mandatory Requirements. Certified under ENERGY STAR Qualified Homes Version 3.
ANSI/ASHRAE Standard 62.2.-2010
Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings. The standard applies to spaces intended for human occupancy in single-family homes and multifamily homes that are three stories or less, including manufactured and modular homes. The standard provides minimum acceptable requirements for mechanical and natural ventilation in these spaces.
This topic is not specifically addressed in the 2009 IECC.
This topic is not specifically addressed in the 2009 IRC.
This topic is not specifically addressed in the 2012 IECC.
This topic is not specifically addressed in the 2012 IRC.
More Info.
High-Efficiency Fans = High-Efficiency Fans
High-efficiency exhaust fans and ceiling fans are more energy efficient and quieter than standard fans.
Alternate Terms
Sales Message
