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Whole house ventilation systems: This article explains how to design, buy, and use a whole house ventilation system to improve indoor air quality in homes.

This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons. But many indoor contaminants are simply too small to see, or are not particles at all but rather gases or chemicals. See ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY for our full list of environmental hazard identification and remedy related to buildings. See VENTILATION in buildings for our full list of building ventilation articles.

© Copyright 2012 InspectAPedia.com, Daniel Friedman, Steve Bliss, Wiley & Sons, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

Whole House Ventilation Strategies for Improving Indoor Air Quality

There are a number of strategies for providing whole-house ventilation, which vary in cost, complexity, and effectiveness. All strategies, however, can be categorized as either exhaust-only, supply-only, or balanced (Below we provide Table 7-1 - Whole House Ventilation Strategies).

Guide to Sizing House Ventilation Systems - How Many CFM of Vent Fan Capacity are Needed?

As detailed in Best Practices Guide to Residential Construction:

ASHRAE Standard 62-1989 recommends a minimum ventilation rate in houses of 15 cfm per person, or .35 air changes per hour (ACH), whichever is greater. Based on the ACH method, a three-bedroom house of 1,500 sq ft with 8 ft ceilings would require:

(1,500 x 8) x .85
x .35 / 60 = 60 cfm

Multiplying the volume by .85 accounts for partitions and exterior wall thickness.

Using the per person method and assuming two people in the master bedroom and one in each other bedroom, the rate is also 60 cfm.

The revised ASHRAE standard 62.2, released in 2003, uses the formula of 7.5 cfm per person (based on the number of bedrooms plus one) plus an factor of .01 cfm for each square foot of house area. For example, based on the new ASHRAE standard, the same three-bedroom, 1,500-square-foot house would require:

(7.5 x 4) / (1,500 x .01) = 45 cfm.

As these calculations show, a low ventilation rate is adequate if run on a continuous basis. A higher continuous rate would be advisable for a home with higher-than-average moisture levels or pollutant sources such as smoking. Intermittent ventilation can also work as long as the total daily ventilation rate is equivalent, but is most effective when the system is timed to operate when people are home breathing air and generating pollutants.

A two-speed or variable-speed fan provides flexibility, allowing the ventilation rate to be raised when needed, for example when painting a room or during a party. More important than the precise number of cubic feet per minute, however, is a well-designed system that is quiet, reliable, and low- maintenance, ensuring it will actually be used.

TABLE 7-1 Whole House Ventilation Strategies

Installation Tips for Whole House Ventilation Systems

Whole-house ventilation systems should be installed by people familiar with the equipment. Since they normally operate at 100 to 200 cfm rather than the much larger fans found in air handlers, they are less forgiving of errors. Numerous field studies have found heat-recovery ventilators performing poorly due to installation errors and poor maintenance.

For good performance with whole-house ventilation systems, follow these general guidelines:

• Size the whole house ventilation system correctly. Oversizing will increase heating and cooling costs.
• Choose quiet, efficient fans in the house ventilation equipment
• Keep HVAC or ventilation duct runs as short and straight as possible.
• Locate fresh air intakes away from pollution sources such as cars, pesticides, and outlets from HVAC equipment or exhaust fans.
• Seal all ducts and insulate where required. Examples: Insulate intake ducts that run though a hot attic or exhaust ducts that pass through a cold, unheated space.
• Integrate spot ventilation in bathrooms or provide separately.
• Use separate spot ventilation in kitchens due to grease.
• Place supply registers high on walls and away from beds, sofas, chairs, and other places likely to cause occupant discomfort.
• Keep controls as simple and automatic as possible.
• Educate homeowners about the system and maintenance requirements.

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

Questions & Answers regarding this article

Questions & answers about how to buy, install, use & maintain a whole house ventilation system & ventilation system impacts on indoor air quality.

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Technical Reviewers & References

• InspectAPedia.com^® - Daniel Friedman - Publisher & Editor.
• Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
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  VENTILATION, WHOLE HOUSE STRATEGIES

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
• 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.
• Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
• Historic Preservation Technology: A Primer, Robert A. Young, Wiley (March 21, 2008) ISBN-10: 0471788368 ISBN-13: 978-0471788362

Air Leaks, Moisture Problems, Vapor Barriers & Ventilation in buildings - References, Products

• Basement Moisture Control, U.S. Department of Energy
• Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF] ISBN-10: 0471331724 ISBN-13: 978-0471331728
• Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008) ISBN-10: 1405161035 ISBN-13: 978-1405161039
• Crawl Space Moisture Control, U.S. Department of Energy
• Energy Recover Ventilation Systems for buildings, U.S. Department of Energy
• Energy Savings Methods: Whole House Systems Approach, U.S. Department of Energy
• Log Homes: Minimizing Air Leakage in Log Homes, U.S. Department of Energy
• Log Homes: Controlling Moisture in Log Homes, U.S. Department of Energy
• Log Homes: Log Home Design, U.S. Department of Energy
• Moisture Control in buildings, U.S. Department of Energy
• Moisture Control in Walls, U.S. Department of Energy
• Quality Standards for the Professional Remodeling Industry, National Association of Home Builders Remodelers Council, NAHB Research Foundation, 1987.
• Quality Standards for the Professional Remodeler, N.U. Ahmed, # Home Builder Pr (February 1991), ISBN-10: 0867183594, ISBN-13: 978-0867183597
• Natural Ventilation for buildings, U.S. Department of Energy
• R-Value of Wood, U.S. Department of Energy
• Spot Ventilation for houses, U.S. Department of Energy
• Slab on Grade Foundation Moisture and Air Leakage, U.S. Department of Energy
• Straw Bale Home Design, U.S. Department of Energy
• "Vapor Barriers or Vapor Diffusion Retarders", U.S. DOE: how vapor barriers work, types of vapor diffusion barriers, installing vapor barrier
• Ventilation for energy efficient buildings, Purpose, Strategies, etc.,
• Weather-Resistive Barriers, how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
• Whole House Ventilation Systems, U.S. Department of Energy
• Whole-House Balanced Ventilation Systems, U.S. Department of Energy
• Whole-House Exhaust Ventilation Systems, U.S. Department of Energy
• Whole-House Supply Ventilation Systems, U.S. Department of Energy