# Large Building Air Leakage Test Calculator.

Online calculator analyzes the air
flows required to pressure test
the airtightness of a large
building with calibrated fans.

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This page includes a online calculator that analyzes the flows required to test the airtightness of a large building by pressurization or depressurization with one or more calibrated fans. The calculator uses javascript, and it will not work if your web browser does not support javascript, or if you do not have javascript enabled.

The calculations default to recent UK airtightness recommendations for "ATTMA Normal Practice" and "ATTMA 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:

Table 1: ATTMA Air Leakage Index (m3/hr/m2 [cfm/ft2] {L/s/m2} @ 50Pa)
Building Type ATTMA Best Practice Leakage Index ATTMA Normal Practice Leakage Index
Offices (naturally ventilated) 3.0 [0.1641] {0.83} 7.0 [0.3828] {1.94}
Offices (mixed mode ventilation) 2.5 [0.1367] {0.694} 5.0 [0.2735] {1.39}
Offices (air conditioned/low energy) 2.0 [0.1094] {0.56} 5.0 [0.2735] {1.39}
Factories/Warehouses 2.0 [0.1094] {0.56} 6.0 [0.3281] {1.67}
Superstores 1.0 [0.0547] {0.28} 5.0 [0.2735] {1.39}
Schools 3.0 [0.1641] {0.83} 9.0 [0.4922] {2.50}
Hospitals 5.0 [0.2735] {1.39} 9.0 [0.4922] {2.50}
Museums and Archival Stores 1.0 [0.0547] {0.28} 1.5 [0.0828] {0.42}
Cold Stores 0.2 [0.0109] {0.056} 0.35 [0.0191] {0.097}
Dwellings (naturally ventilated) 3.0 [0.1641] {0.83} 9.0 [0.4922] {2.50}
Dwellings (mechanically ventilated) 3.0 [0.1641] {0.83} 5.0 [0.2735] {1.37}

An "Old Practice Leakage Index" has been included in the calculator below that defaults to twice the UK "ATTMA Normal Practice Leakage Index" in order to expand the range of the calculations to include older buildings.

These 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 71-9265 m3/h (42-5450 cfm) @ 50 Pa) and for large mobile fans (e.g. the Infiltec G54 mobile fan with flows of 7-26 m3/s (15-55 kcfm) @ 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 256,000 m3 (9,000,000 ft3) food distribution warehouse in Manchester, UK.

 ONLINE BUILDING LEAKAGE CALCULATOR IN METRIC UNITS: (click here for US Units) ------------------------------------------------------------ Instructions: you can type your building dimension INPUT DATA into the boxes below, and the building leakage CALCULATED DATA will be updated for your entries: ------------------------------------------------------------ INPUT DATA: Building Dimensions: (type your building data into each box to replace the defaults) Total Building Floor Area: square meters. Height of 1 Story: meters. Number of Stories: . Ratio of Length to Width (input 1 when Length=Width, 2 when Length=2xWidth, etc.) ------------------------------------------------------------ Calculations: all of the building leakage data below is calculated from the building dimension INPUT DATA above that you have entered or from the default values. Do not enter data in the CALCULATED DATA boxes below. To update all of the calculations below, click on any of the CALCULATED DATA boxes. To return to the default values, press your browser refresh button. ------------------------------------------------------------ CALCULATED DATA: Calculated Building Dimensions: (click on any box to recalculate all boxes) Building Width: meters. Building Length: meters. Building Surface Area: square meters (includes envelope floor, wall and ceiling). Building Volume: cubic meters. Calculated Maximum Allowable Test Flow @ 50 Pa if Building Just Meets Leakage Index: (click on any box to recalculate all boxes) Old Practice Leakage Index flow (10 m3/hr/m2 or 2.78 L/s/m2 or 0.5469 cfm/ft2 @ 50 Pa): m3/h or L/s or m3/s. ATTMA Normal Practice Leakage Index flow (5 m3/hr/m2 or 1.39 L/s/m2 or 0.2734 cfm/ft2 @ 50 Pa): m3/h or L/s or m3/s. ATTMA Best Practice Leakage Index flow (2.5 m3/hr/m2 or 0.694 L/s/m2 or 0.1367 cfm/ft2 @ 50 Pa): m3/h or L/s or m3/s. NOTE 1: the default Normal and Best Leakage Practice for office buildings operating in mixed mode are from the ATTMA March 2006 standard. NOTE 2: An Old Practice Leakage Practice has been included in the calculator below that defaults to twice the UK "ATTMA Normal Practice Leakage Index" in order to expand the range of the calculations to include older leakier buildings. NOTE 3: if the test is done at pressures other than 50 Pa, then scale flow by the ratio of test pressure divided by 50 Pa to the 0.65 power. For example, if the test is done at 75 Pa, then the flow shown above is increased by (75/50)^.65 = 1.30. NOTE 4: for other leakage indexes, the flows above scale proportional to the leakage index. For instance, if the desired leakage index is 1.0 m3/hr/m2, then the flows for this index are 1/10 of the flows for the leakage index of 10 m3/hr/m2 (Old Practice). Maximum Allowable Leak Area If Building Just Meets Leakage Index: (click on any box to recalculate all boxes) Old Practice Leakage Index (10 m3/hr/m2 or 2.78 L/s/m2 or 0.5469 cfm/ft2 @ 50 Pa) equivalent area: square meters. ATTMA Normal Practice Leakage Index (5 m3/hr/m2 or 1.39 L/s/m2 or 0.2734 cfm/ft2 @ 50 Pa) equivalent area: square meters. ATTMA Best Practice Leakage Index (2.5 m3/hr/m2 or 0.694 L/s/m2 or 0.1367 cfm/ft2 @ 50 Pa) equivalent area: square meters. NOTE 1: Assumes building cracks have a pressure exponent of 0.65. NOTE 2: for other leakage indexes, the leakage areas above scale proportional to the leakage index. For instance, if the desired leakage index is 1.0 m3/hr/m2, then the leakage areas for this index are 1/10 of the flows for the leakage index of 10 m3/hr/m2 (Old Practice). Number of E3 Stacked Blower Door Fans Required For Test: (click on any box to recalculate all boxes) Old Practice Leakage Index (10 m3/hr/m2 or 2.78 L/s/m2 or 0.5469 cfm/ft2 @ 50 Pa): E3 fans. ATTMA Normal Practice Leakage Index (5 m3/hr/m2 or 1.39 L/s/m2 or 0.2734 cfm/ft2 @ 50 Pa): E3 fans. ATTMA Best Practice Leakage Index (2.5 m3/hr/m2 or 0.694 L/s/m2 or 0.1367 cfm/ft2 @ 50 Pa): E3 fans. NOTE 1: the E3 calibrated flow is 71-9265 m3/h (42-5450 cfm) @ 50 Pa, and 3 fans can be stacked in each doorway. NOTE 2: for other leakage indexes, the number of E3 fans above scale proportional to the leakage index. For instance, if the desired leakage index is 1.0 m3/hr/m2, then the flows for this index are 1/10 of the E3 fans for the leakage index of 10 m3/hr/m2 (Old Practice). Number Of G54 Mobile Fans Required For Test: (click on any box to recalculate all boxes) Old Practice Leakage Index (10 m3/hr/m2 or 2.78 L/s/m2 or 0.5469 cfm/ft2 @ 50 Pa): G54 fans. ATTMA Normal Practice Leakage Index (5 m3/hr/m2 or 1.39 L/s/m2 or 0.2734 cfm/ft2 @ 50 Pa): G54 fans. ATTMA Best Practice Leakage Index (2.5 m3/hr/m2 or 0.694 L/s/m2 or 0.1367 cfm/ft2 @ 50 Pa): G54 fans. NOTE 1: the G54 calibrated flow is 7-26 m3/s (15-55 kcfm) @ 50 Pa, and predicted flows below 40% of maximum may not permit a full multi-point test covering 20-60 Pa. NOTE 2: for other leakage indexes, the G54 fans above scale proportional to the leakage index. For instance, if the desired leakage index is 1.0 m3/hr/m2, then the G54 fans for this index are 1/10 of the fans for the leakage index of 10 m3/hr/m2 (Old Practice). Air Changes Per Hour at 50 Pa: (click on any box to recalculate all boxes) Old Practice Index (10 m3/hr/m2 or 2.78 L/s/m2 or 0.5469 cfm/ft2 @ 50 Pa): ACH50. ATTMA Normal Practice Leakage Index (5 m3/hr/m2 or 1.39 L/s/m2 or 0.2734 cfm/ft2 @ 50 Pa): ACH50. ATTMA Best Practice Leakage Index (2.5 m3/hr/m2 or 0.694 L/s/m2 or 0.1367 cfm/ft2 @ 50 Pa): ACH50. NOTE 1: Compare to a 1 story, 150 m2 (1500 ft2), 3m (10ft) high house, where Old Practice = 10 ACH50, ATTMA Normal Practice = 5 ACH50, and ATTMA Best Practice = 2.5 ACH50. NOTE 2: for other leakage indexes, the ACH50 above scale proportional to the leakage index. For instance, if the desired leakage index is 1.0 m3/hr/m2, then the ACH50 for this index are 1/10 of the flows for the leakage index of 10 m3/hr/m2 (Old Practice). Please send calculator problem reports and comments to .
For further assistance, call Infiltec toll free at (888) 349-7236 or (540) 943-2776.

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