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Bathroom Ventilation Design Recommendations
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This article discusses the proper design, location, control, and ducting of bathroom vent fans and bath vent duct work. We also discuss the issue of bath vent fan noise, proper location of bath vent controls, and bath vent duct condensation problems.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Bathroom Ventilation Design Recommendations
 Also see our home page on bathroom venting found at BATHROOM VENTILATION, and the general topic of building ventilation: VENTILATION in BUILDINGS.
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. This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.
Our photo (left) illustrates location of a bathroom exhaust vent over the shower stall - placed to maximize the effectiveness of exhaust of moisture during shower use. We used a GFCI circuit to assure safety for anyone changing bulbs in this fixture. Photo courtesy Galow Homes.
As noted in Chapter 6 of Best Practices Guide to Residential Construction:
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. Bathrooms produce
moisture, odors, and VOCs from aerosols and various personal
hygiene products. Effective spot ventilation in these
areas is critical for maintaining healthy levels of indoor
humidity levels and an overall healthy indoor environment
(see INDOOR AIR QUALITY IMPROVEMENT GUIDE).
Bathroom ventilation should be powerful enough to remove
excess moisture before it has time to condense on
cold walls and windows, potentially damaging finishes, or
escape into wall or ceiling cavities, where it may lead to
decay or peeling paint.
Ventilation Rate Required for Bathrooms
The minimum ventilation rate for
bathrooms required by the 2003 International Residential
Code (IRC) is 50 cfm intermittent or 20 cfm continuous
(if part of a whole-house ventilation system). While this
may be adequate for a small bath, the guidelines of the
Home Ventilating Institute (HVI) are more suitable for
larger rooms:
- Small baths: For bathrooms up to 100 sq ft, HVI recommends
using an exhaust fan that provides 1 cfm per
square foot of floor space. This will provide approximately
8 air changes per hour. So, for example,
an 8x10-foot bathroom would require 80 cfm of
ventilation.
- Large baths: For bathrooms over 100 sq ft, the HVI
recommends a ventilation rate based on the number
and type of fixtures as shown in Table 6-12. For
example, a bathroom with a toilet, shower, and jetted
tub would require 200 cfm (50 + 50 + 100) of ventilation
either in a single fan or multiple fans placed
over the fixtures being vented.
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Table 6-12
[Click any image or table to see an enlarged version with additional detail, commentary & source citation.] |
Bath Fan Noise Issues
The biggest homeowner objection to bath fans,
their noise, has been addressed with the introduction of
whisper-quiet bath fans from a number of manufacturers.
Choose the quietest fan for the job, preferably one rated
1.5 sones or less (one sone roughly equals the sound of a
quiet refrigerator motor).
Recommendations for Bathroom Fan Location
 For optimal ventilation, locate the
exhaust grilles near the source to be ventilated, typically
over the tub or shower. In smaller baths, a single, central
exhaust point is usually adequate, while in larger baths,
multiple smaller fans (or a remote fan with separate pickups)
will be more effective.
Bathrooms with enclosed toilet
areas or steam showers should have separate exhaust
grilles in those areas. Since all exhaust fans require
makeup air, the bathroom door needs to be undercut to provide
makeup air when bathroom windows are closed.
Our photo (left) illustrates location of a bathroom exhaust vent over the shower stall - placed to maximize the effectiveness of exhaust of moisture during shower use. We used a GFCI circuit to assure safety for anyone changing bulbs in this fixture. Photo courtesy Galow Homes.
Advice for Bath Fan Controls
The Home Ventilating Institute (HVI) recommends
that a fan be left on for 20 minutes after use of a bath
or shower to remove all excess moisture from the room and
ductwork. A timer switch is the simplest way to accomplish
this.
Another option is a dehumidistat switch, which will
automatically operate the fan whenever the humidity level
rises above a preset level. A manual override allows normal
operation of the fan for other bathroom uses.
Bath Fan Ductwork Specifications
Examples of good, bad, and horrible fan duct work installations are found at our bath venting home page: BATHROOM VENTILATION
A ventilating fan must overcome the resistance,
called “static pressure,” created by the ductwork, including
transitions, elbows, and the wall or roof cap. The
advertised airflow of bath fans is typically based on a static
pressure of 0.1 (inches of water gauge) although some also
publish the airflow rating at 0.25 inches, which gives a
better estimate of actual airflow in most installations.
A
static pressure of 0.1 is roughly equivalent to 15 feet of
straight, smooth 4-inch duct with a 100 cfm fan. A typical
installation with about 20 feet of duct, two elbows, and a
wall cap has an equivalent duct length closer to 80 feet (see Table 6-13).
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Table 6-13
[Click any image or table to see an enlarged version with additional detail, commentary & source citation.] |
How well a particular fan can overcome the ductwork’s
resistance to airflow is highly variable and is indicated
by its fan curve, available from the manufacturer.
Inline fans mounted remotely and exterior fans are generally
the most powerful.
A typical installation with two
elbows and 20 to 30 feet of duct reduces the rated airflow
of a standard fan by anywhere from 10 to 30%. With long
runs, multiple elbows, or corrugated flex duct, airflow
may be reduced by 50% or more. To ensure good airflow,
follow these guidelines:
- Use smooth ductwork of the same size or slightly
larger than the fan outlet. Thin-walled PVC pipe
works well and is easy to seal.
- Keep duct runs as short and straight as possible.
- Where possible, use broad sweeps rather than
90-degree angles to change direction.
- Seal all joints in metal duct with foil-backed tape or
duct mastic, not cloth duct tape.
- For a standard installation, choose a slightly larger fan
size than required. Where duct runs exceed about
25 feet plus two elbows, choose a larger fan size and
check the fan curve to determine actual airflow.
Condensation in ductwork is also a concern in cold
climates. To avoid problems, insulate the ductwork to at
least R-5 or run it below the ceiling insulation. Also keep
any metal duct seams facing upward and slope the duct
slightly toward the exterior outlet so that any condensation
drains to the outside. Avoid any sags in the ductwork,
which are potential pooling areas for condensation.
Kitchen and Bath Product Manufacturers, Sources, Associations
Bath Fan Manufacturers
American Aldes
www.americanaldes.com
Remote location single- and multi-port exhaust ventilators
Broan-Nutone LLC
www.broan.com
Low-sone Broan bath fans, also single- and multiport
remote location exhaust ventilators; Nutone ceiling-mount
bath fans
Fan Tech
www.fantech.com
Remote location inline-duct fans
Kanalflakt
www.kanalflakt.com
Remote location inline-duct fans
Marley Engineered Products
www.marleymeh.com
Ceiling-mount bath fans and general kitchen and room
exhaust fans
Panasonic
www.panasonic.ca/English/ventilationfans
Low-sone, Energy-Star-compliant ceiling-mount, inline,
and wall bath fans
Kitchen Exhaust Fan Companies
Amana
www.amana.com
Pop-up and traditional range hoods
Bosch
www.boschappliances.com
Chimney style, downdraft, and traditional range hoods,
stainless steel and colors
Kitchenaid
www.kitchenaid.com
Retractable downdraft, slide out, island, and traditional
range hoods
Broan-Nutone LLC
www.nutone.com
Nutone downdraft, island, and traditional range hoods
Dacor
www.dacorappl.com
Commercial-style, stainless-steel pop-up and overhead
range hoods; hood liners for custom canopies
Gaggenau
www.gaggenau.com/us
Chimney-style, pop-up, slide-out, and island range hoods
in stainless-steel, aluminum, and glass
Jenn Aire/Maytag Corp
www.jennaire.com
Pop-up, under-cabinet, wall, soffit, island, and fans and
hood liners for custom canopies
Thermador
www.thermador.com
Updraft, downdraft, and island-range hoods
Wolf Appliance Co.
www.wolfappliance.com
Pop-up, chimney-style, wall, and island-range hoods
in stainless steel
Kitchen & Bath Industry Associations
Association of Home Appliance Manufacturers(AHAM)
www.aham.org
National Kitchen and Bath Association (NKBA)
www.nkba.org
Ceramic Tile Institute of America
www.ctioa.org
Home Ventilation Institute (HVI)
www.hvi.org
Marble Institute of America
www.marble-institute.com
Porcelain Enamel Institute (PEI)
www.porcelainenamel.com
Tile Council of America (TCA)
www.tileusa.com
-- Adapted with permission from Best Practices Guide to Residential Construction.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
- Eric Galow, Galow Homes, Lagrangeville, NY. Mr. Galow can be reached by email: ericgalow@gmail.com or by telephone: 914-474-6613. Mr. Galow specializes in residential construction including both new homes and repairs, renovations, and additions.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- "The Elimination of Unsafe Guardrails, a Progress Report," Elliott O. Stephenson, Building Standards, March-April 1993
- "Are Functional Handrails Within Our Grasp" Jake Pauls, Building Standards, January-February 1991
- Access Ramp building codes:
- UBC 1003.3.4.3
- BOCA 1016.3
- ADA 4.8.2
- IBC 1010.2
- Access Ramp Standards:
- ADA (Americans with Disabilities Act), Public Law 101-336. 7/26/90 is very often cited by other sources for good design of stairs and ramps etc. even where disabled individuals are not the design target.
- ANSI A117.4 Accessible and Usable buildings and Facilities (earlier version was incorporated into the ADA)
- ASTM F 1637, Standard Practice for Safe Walking Surfaces, (Similar to the above standards)
- America's Favorite Homes, mail-order catalogues as a guide to popular early 20th-century houses, Robert Schweitzer, Michael W.R. Davis, 1990, Wayne State University Press ISBN 0814320066 (may be available from Wayne State University Press)
- American Plywood Association, APA, "Portland Manufacturing Company, No. 1, a series of monographs on the history of plywood manufacturing",Plywood Pioneers Association, 31 March, 1967, www.apawood.org
- ASHRAE resource on dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries. The following three ASHRAE Handbooks are also available at the InspectAPedia bookstore in the third page of our Insulate-Ventilate section:
- 2005 ASHRAE Handbook : Fundamentals : Inch-Pound Edition (2005 ASHRAE HANDBOOK : Fundamentals : I-P Edition) (Hardcover), Thomas H. Kuehn (Contributor), R. J. Couvillion (Contributor), John W. Coleman (Contributor), Narasipur Suryanarayana (Contributor), Zahid Ayub (Contributor), Robert Parsons (Author), ISBN-10: 1931862702 or ISBN-13: 978-1931862707
- 2004 ASHRAE Handbook : Heating, Ventilating, and Air-Conditioning: Systems and Equipment : Inch-Pound Edition (2004 ASHRAE Handbook : HVAC Systems and Equipment : I-P Edition) (Hardcover)
by American Society of Heating, ISBN-10: 1931862478 or ISBN-13: 978-1931862479
"2004 ASHRAE Handbook - HVAC Systems and Equipment The 2004 ASHRAE HandbookHVAC Systems and Equipment discusses various common systems and the equipment (components or assemblies) that comprise them, and describes features and differences. This information helps system designers and operators in selecting and using equipment. Major sections include Air-Conditioning and Heating Systems (chapters on system analysis and selection, air distribution, in-room terminal systems, centralized and decentralized systems, heat pumps, panel heating and cooling, cogeneration and engine-driven systems, heat recovery, steam and hydronic systems, district systems, small forced-air systems, infrared radiant heating, and water heating); Air-Handling Equipment (chapters on duct construction, air distribution, fans, coils, evaporative air-coolers, humidifiers, mechanical and desiccant dehumidification, air cleaners, industrial gas cleaning and air pollution control); Heating Equipment (chapters on automatic fuel-burning equipment, boilers, furnaces, in-space heaters, chimneys and flue vent systems, unit heaters, makeup air units, radiators, and solar equipment); General Components (chapters on compressors, condensers, cooling towers, liquid coolers, liquid-chilling systems, centrifugal pumps, motors and drives, pipes and fittings, valves, heat exchangers, and energy recovery equipment); and Unitary Equipment (chapters on air conditioners and heat pumps, room air conditioners and packaged terminal equipment, and a new chapter on mechanical dehumidifiers and heat pipes)."
- 1996 Ashrae Handbook Heating, Ventilating, and Air-Conditioning Systems and Equipment: Inch-Pound Edition (Hardcover), ISBN-10: 1883413346 or ISBN-13: 978-1883413347 ,
"The 1996 HVAC Systems and Equipment Handbook is the result of ASHRAE's continuing effort to update, expand and reorganize the Handbook Series. Over a third of the book has been revised and augmented with new chapters on hydronic heating and cooling systems design; fans; unit ventilator; unit heaters; and makeup air units. Extensive changes have been added to chapters on panel heating and cooling; cogeneration systems and engine and turbine drives; applied heat pump and heat recovery systems; humidifiers; desiccant dehumidification and pressure drying equipment, air-heating coils; chimney, gas vent, fireplace systems; cooling towers; centrifugal pumps; and air-to-air energy recovery. Separate I-P and SI editions."
- Principles of Heating, Ventilating, And Air Conditioning: A textbook with Design Data Based on 2005 AShrae Handbook - Fundamentals (Hardcover), Harry J., Jr. Sauer (Author), Ronald H. Howell, ISBN-10: 1931862923 or ISBN-13: 978-1931862929
- Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
- Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
- How could homes be designed and built more efficiently?
- What kinds of construction and production techniques worked well and which did not?
- How did people use different kinds of spaces in their homes?
- What roles did community planning, zoning, and interior design play in how neighborhoods worked
- The Circular Staircase, Mary Roberts Rinehart
- Energy Savers: Whole House Systems Approach to Energy Efficient Home Design [copy on file as /interiors/Whole_House_Energy_Efficiency_DOE.pdf ] - U.S. Department of Energy
- "Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
- "Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
- "Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
- "Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
- Gypsum Construction Guide, National Gypsum Corporation
- Gypsum
Construction Handbook [purchase at Amazon.com] H17, Technical
Folder SA920 and PM2, PM3 and PM4, United States Gypsum Company, 125 South Franklin ST., PO Box 806278, Chicago, IL 60680-4124,
- Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
- Ice Dam Leaks in building attics and roof cavities, how to inspect for evidence of leaks, identify causes, and
- What Style Is It?: A Guide to American Architecture, Rev., John C. Poppeliers, S. Allen Chambers, Wiley; Rev Sub edition (October 6, 2003), ISBN-10: 0471250368, ISBN-13: 978-0471250364
- ...
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