Infiltec blower door test courtesy Steve Bliss - Solar Age

Pascal Calculations & Building Air Infiltration Rate Variation

Calculating pressure in Pascals
- Accuracy in measuring air infiltration rates in buildings
- Air infiltration rate rules of thumb
- Sources of variation in building air infiltration rates & measurements
- Measuring air leakage using a blower door
- Building air changes per hour and blower door tests
- Using a blower door test to improve building energy efficiency & save on heating cost
- Explanation of testing building indoor air movement using air handlers and other fans instead of a blower door - data beyond air infiltration or exfiltration.
Questions & answers about pascal calculations, building air infiltration rate, building air exchange rate, ACH or air changes per hour rates
References

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This article explains methods of measuring building air infiltration rates and the related calculations of pascals. This website discusses how to inspect, diagnose problems in, and install or repair building insulation & ventilation systems including air leaks, air infiltration, heating cost, heat loss, moisture, & interior stains. Readers should also see AIR LEAK DETECTION TOOLS (including an example of use of the blower door test to measure building air changes per hour) and see INDOOR AIR QUALITY IMPROVEMENT GUIDE which includes details about whole house ventilation systems. Our page top photo, courtesy of Steven Bliss, shows an Infiltec blower door test being performed at a home. Accompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Building Air Infiltration Rates & How to Calculate Pascals

Q&A on use of Pascal Calculation - original text. Use your browser's back button to return to this page

The question-and-answer article about Pascals and using rules of thumb to estimate building air infiltration rates based on blower door tests found just below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Pascal-Calculations

I am confused by a slight lack of consistency in magazine articles about air leakage rates. Solar Age Magazine February 1984 p. 47 said that to get the normal air leakage you divide the building air changes per hour (ACH) at 50 Pascals [of pressure, e.g. by blower door testing] by 7.

But the May 1984 issue of the same magazine said 10 ACH at 50 Pascals equals roughly 0.5 natural ACH (dividing by 20). Which one is correct? -- Joe Bockelman, Dayton OH

Answer: Building air infiltration rate rules of thumb

Definition of Pascals (Pa): Pascals is a unit of measurement of pressure or an SI derived unit of pressure or stress. Pascal measurements are used in evaluating building air infiltration rates, often using blower door tests, where relatively small absolute pressure differences become important, so we need a sensitive unit of measurement.

One Pascal or Pa equals one newton per square meter; one bar of pressure equals 100,000 Pa, one atmosphere equals 101,325 Pa, and one psi equals 6.894 x 10³ Pa.

A widely accepted rule of thumb for estimating the natural winter air infiltration rate in a building is to divide the ACH at 50 Pascals by 20.

This is most appropriate for a single-story detached house with no unusual wind loads.

This rough rule of thumb on air infiltration rates works pretty well for averages of large samples of homes, yet for a single home, it is not very reliable.

For example, the average air infiltration rate at 50 Pascals of 35 passive solar homes monitored by SERI was 11.1 ACH. The average natural infiltration rate of this sample (as measured by tracer gas) was 0.5.

So dividing by 20 would have worked well for the average.

Variation in Individual Building Air Infiltration Rates

However, for individual homes in this sample, the correct divisor ranged from 10 to 40. The wind speed, shape of the house, location of the cracks and air leaks, temperature differences, and use of combustion equipment all play a role.

A given number tends to work pretty well for a given type of house under similar conditions. The natural ACH in a single house, though, may change by as much as a factor of 10 depending on the time of year and weather variables.

See AIR SEALING STRATEGIES and also AIR LEAK DETECTION TOOLS for details about sealing air leaks in buildings. See BRICK VENEER WALL INSULATION for a discussion of leaks at brick veneer walls insulated with foam board.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

"Enter the Blower Door", Steve Bliss, Solar Age, February 1984, p. 46-47 -- Adapted with permission, from original material to form this web page article.
Sources of blower doors and more blower door test information:
- Princeton University's Center for Energy and Environmental Studies, http://www.princeton.edu/pei/energy/
- Retrotec Blower Door Sources: www.retrotecblowerdoor.com/ Minneapolis Blower Door Source Information
- Infiltec Blower Door Sources: Lightweight blower door and instrumentation are available from Infiltec - see their online catalog at www.infiltec.com/inf-catb.htm
- The Energy Conservatory Blower Door Source: - www.energyconservatory.com/products/products4.htm

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.

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.

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Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
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
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