The calculations default to recent UK airtightness recommendations for "Normal Practice" and "Best Practice" for office buildings with mixed mode ventilation from the UK Air Tightness Testing and Measurement Association (ATTMA) test standard Technical Standard 1: Measuring the Air Permeability of Building Envelopes (TS1). The full list of ATTMA building air leakage recommendations in Metric and US units is shown in Table 1 below:
|Building Type||Best Practice Leakage Index||Normal Practice Leakage Index|
|Offices (naturally ventilated)||3.0 [0.1641]||7.0 [0.3828]|
|Offices (mixed mode ventilation)||2.5 [0.1367]||5.0 [0.2735]|
|Offices (air conditioned/low energy)||2.0 [0.1094]||5.0 [0.2735]|
|Factories/Warehouses||2.0 [0.1094]||6.0 [0.3281]|
|Superstores||1.0 [0.0547]||5.0 [0.2735]|
|Schools||3.0 [0.1641]||9.0 [0.4922]|
|Hospitals||5.0 [0.2735]||9.0 [0.4922]|
|Museums and Archival Stores||1.0 [0.0547]||1.5 [0.0828]|
|Cold Stores||0.2 [0.0109]||0.35 [0.0191]|
|Dwellings (naturally ventilated)||3.0 [0.1641]||9.0 [0.4922]|
|Dwellings (mechanically ventilated)||3.0 [0.1641]||5.0 [0.2735]|
An "Old Practice Leakage Index" has been included in the calculator below that defaults to twice the UK "Normal Practice Leakage Index" in order to expand the range of the calculations to include older buildings.
These leakage index recommendations are based on leakage per surface area and not the commonly used air changes per hour (ACH) comparison used for smaller residential buildings. When the buildings of different size are compared, ACH does not provide a good comparison between buildings, and leakage per surface area comparisons provide a better measure of envelope construction quality. The online calculator below is provided as an introduction to large building air leakage testing, and it should not be used for actual testing.
One problem with large building tests is determining the type and quantity of fans necessary to perform a test. The online calculator estimates the number of fans required, both for blower door fans (e.g. the Infiltec E3 stacked blower door fan with up to 3 fans in each doorway and each fan capable of flows of 100-5450 cfm @ 50 Pa) and for large mobile fans (e.g. the Infiltec G54 mobile fan with flows of 15,000-55,000 cfm @ 50 Pa). Experience has shown that is undesirable to arrive at a test with either too much fan capacity or too little fan capacity.
For more information on large building air leakage testing, see the Infiltec Large Building Envelope Airtightness page. Click here to see pictures of a test of a 9,000,000 ft3 (256,000 m3) food distribution warehouse in Manchester, UK.