Measuring Building Airtightnesswith a Blower Door

Gary NelsonThe Energy Conservatory

Minneapolis, MNwww.energyconservatory.com

Hidden Construction DetailsOften the largest and most important air leaks

Hidden Construction Details

Duct LeakageIn some homes, this is the highest priority

(particularly in the sun belt)

Why Airtightness Matters

• Durability of building components - moisture condensation in components.

• Comfort.• Energy use. • Indoor air quality.• Reducing callbacks and risk.

Purposes of a Blower Door Test

• Document the air tightness of houses (are they leaky - tight -or somewhere in between) and compare to program standards.

• Help find air leaks by inducing air to move through all leaks atthe same time (chemical smoke, IR camera, feeling with you hand, zonal pressures).

• Help determine the need for mechanical ventilation by estimating natural infiltration rates.

• Investigate duct leakage problems. • Determine the effectiveness of air sealing activities (compare

before and after measurements).• Estimate design infiltration loads for heating and cooling.

Purposes of a Blower Door Test

• Note: Blower Doors do not directly measure natural infiltration rates. They measure air tightness (e.g. how big isthe hole in the building envelope) and infiltration rates are mathematically estimated using infiltration models. Infiltration estimates may be off by 50% or more.

Blower Door Equipment

• Adjustable aluminum frame and nylon panel.

• Calibrated fan.• Digital pressure gauge to

measure building and airflow through the fan.

Preparing the House for a Test

• Close all exterior doors and windows.• Open all interior doors.• Adjust spillage susceptible combustion appliances so they do

not turn on during the test.• Turn off all exhaust appliances.• Close fireplace and woodstove doors.• Other intentional openings may be sealed depending on

program guidelines.

Blower Door Test (single point)

• Blower Door fan is used to depressurize (blow air out) or pressurize (blow air into) the house.

• Adjust fan until the house pressure is changed by 50 Pa. (approx. pressure caused by 20 mph wind)

• Flow through the fan needed to create a 50 Pa change is one metric of house air tightness (CFM@50).

Supply

Return

BlowerDoorFan

Crawlspace

Attic

-50-50

Blower Door Test

Supply

Return

BlowerDoorFan

Crawlspace

Attic

-50-50

• Blower Door readings can also be expressed as total equivalent hole size (square inches).

• Can also normalize for house size. One method is to normalize for volume (ACH@50). – <1.5 - very tight– 1.5 to 3 - tight– 3 to 6 - typical pretty good

new construction or retrofit– 6 to 10 - leaky– 10 to 20 - very leaky

Tightness Standards

• Air tightness standards often normalize by building envelope area.• ASHRAE 90.1-2004 Addendum z (proposed) standard is

.4CFM@75Pa/ft2 (≈.31CFM@50Pa/ft2)• Building America (DOE) standard is .25CFM@50Pa/ft2

• UK standard is .55CFM@50Pa/ft2. Testing required for commercial buildings >1000m2 since 2002. Houses are type tested. Building must also meet the design air permeability used for calculating compliance with the Target Emission Rate (TER)

• Passivhaus standard of .6ACH@50Pa for a 60’X40’X20’ building would be .055CFM@50Pa/ft2. Bemidji Passivhaus is much tighter!

• National Association of Architectural Metal Manufacturers specification: .046 CFM@50Pa/ft2 maximum for walls exclusive of operable windows.

Measurements of Commercial Buildings

• Persily and Grot, 8 US office buildings: .16 to .79 CFM@50Pa/ft2

• Tamura and Shaw, typical wall leakage in Canada:.08, .231, and .46 CFM@50Pa/ft2

for tight, average, and leaky walls.• Persily and Grot measured natural infiltration in 8 new office

buildings: .1 to .6 ACH

Blower Door Fan Basics

flow sensor

• Airflow is determined by measuring flow sensor pressure (with reference to upstream of fan).

• Airflow can only be measured in one direction (from inlet to exhaust).

• Motor is reversible for diagnostic purposes only.

Blower Door Fan Basics

• Flow Rings are needed when measuring flows below 2,400 cfm (tight houses).

• Failure to use Flow Rings can lead to large errors.

• Pressure gauge will indicate if a Flow Ring is needed.

Fan Configuration Flow Range (cfm) forModel 3 Fan

Open (no Flow Ring) 6,300 - 2,400Ring A 3,000 - 900Ring B 1,000 - 300

Digital Pressure Gauge

• DG-700 is a 2 channel differential pressure gauge.

• Simultaneous display of both house pressure and fan flow readings.

• Proper tubing connections and gauge settings are critical.

Other Tests Using A Blower Door

• Air Leakage Path investigation– Blower Door with an

Infrared Camera.– View wall before

Blower Door test– View wall with

Blower Door running.– Changes in IR images

are caused by air leakage.

– Handheld smoke puffer.

Other Tests Using A Blower Door

• Duct Leakage Diagnostics – Pressure Pan test to quickly

determine if duct work is connected to the outside. With Blower Door maintaining 50 Pa, test registers with Pressure Pan.

– Blower Door subtraction measures duct leakage to outside by comparing Blower Door test – one with registers open and one with registers sealed.

Other Tests Using A Blower Door

• Zone Pressure Testing– Measure pressure change in

attached unconditioned zones (e.g. attic) with Blower Door running.

– Helps to quickly identify dominant house leaks.

– Can be used to quantify leakage rates, but method is complicated.

Blower Door Software

• TECTITE software is used to calculate air tightness results including:– Air tightness metrics (cfm50,

ACH50, leakage areas, other normalized leakages and building leakage curve).

– Infiltration rates (both design and average annual).

– Recommended mechanical ventilation (based on ASHRAE 62.2).

– Estimated cost of infiltration.

Automated Testing with a DG-700

• Computer required. • TECTITE Software.• Fan control cable.• Serial cable.

Advantages of Automated Tests

• Quickly collect thousands of test data points which improves test accuracy in windy weather.

• Allows better estimates of leakage areas by measuring at multiple building pressures.

• Reduces operator errors and increases consistency between tests by providing operator prompts.

Data Logging with the DG-700

• Connect DG-700 to laptop and simultaneously record fan depressurization and vent performance.

• TECLOG software is available at no-charge.

More Useful Information• Visit www.energyconservatory.com• Articles on airsealing and duct leakage diagnostics.• All product manuals and guides are online.• Links to other sites.• Demo versions of TECTITE.• BSRIA website has good best practices recommendations for

air tightness of various building types: www.bsria.co.uk• Building Science Corporation website has a wealth of building

science information and recommended details: www.buildingscience.com

• Joe Lstiburek and John Straub here Dec 19 & 20 for a building science course focusing on commercial buildings.