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RED Calc Free Help Air Leakage Metrics
Air Leakage Metrics Tool User Guide

Air Leakage Metrics
Red Calc Tool User Guide

What this tool can do for you

You can calculate up to eight air leakage metrics, including ACH50, equivalent leakage area (EqLA), effective leakage area (ELA), specific leakage area (SLA), and more. Determine if your building complies with the International Energy Conservation Code or Energy Star Qualified Homes requirements for ACH50 or the Washington State requirement for SLA. (See references below.)

This unique RED Calc tool uses our "solve-all" technique, but in a different way than our other solve-all tools. Instead of selecting one of eight values to solve, you select one of eight values to enter; the other seven are solved by the tool.

You will find this tool very useful for determining airtightness code compliance and target tightness values, and for your education.

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Photo courtesy Retrotec

Calculated values

  • Leakage at 50Pa
  • ACH50
  • Equivalent leakage area (EqLA)
  • Effective leakage area (ELA)
  • Specific leakage area
  • Leakage at 50Pa / floor area
  • Leakage at 50Pa / surface area
  • Leakage coefficient

Tips

  • Clicking the label for any input or result will cause a popup help box to appear. This help box includes the allowed and normal values (for inputs). Read more.
  • In the bottom section of the tool, you must select one of the eight metrics with the radio buttons and enter its value. All seven other metrics will be calculated.
  • A few of the calculated results in the bottom section of the tool require that certain input values to be entered in the top section of the tool. For example, "Leakage at 50Pa / floor area" and "Specific leakage area" require that "Floor area" in the top section of the tool be entered. Additionally, "Leakage at 50Pa / surface area" requires the "Surface area" in the top section of the tool to be entered.

Inputs and field measurements

  • Floor area - this is usually the floor area of the building that is exposed to the blower door test. This input is not required. However, the "Specific leakage area" and "Leakage at 50Pa / floor area" results will not be calculated, or used to calculate other results, unless the floor area value is entered.
  • Volume - this is usually the part of the building corresponding to the blower door test. This input is not required. However, "ACH50" will not be calculated, or used to calculate other results, unless the volume is entered.
  • Surface area - this is usually the external surface of the building that is exposed to the blower door test. Some practitioners include only the surface area that is above grade. This input is not required. However, the "Leakage at 50Pa / surface area" result will not be calculated, or used to calculate other results, unless the surface area is entered.
  • Pressure exponent - the default value is 0.65. Unless you know the actual pressure exponent of the building, use this default value. If you have the results from a multipoint blower door test on the building and know the actual pressure exponent, use the actual pressure exponent.
  • One of the following eight metrics in the bottom section must be entered as an input. Click the radio button to select the metric you wish to enter; the seven other metrics will be calculated.
    • Leakage at 50Pa - results of your blower door test.
    • ACH50 - the building air changes per hour at 50 pascals of pressure, or the building leakage airflow at 50Pa normalized by the house volume. See the International Energy Conservation Code for ACH50 requirements for different climate zones in the U.S (see map below).
    • Equivalent leakage area (EqLA) - The cross-sectional area of a sharp-edged hole that would have the same leakage flow rate as the building if both were subjected to a 10 pascal indoor/outdoor pressure difference. This metric is the origin of the "CFM50 divided by 10" rule.
    • Effective leakage area (ELA) - The cross-sectional area of an orifice hole (shaped like the blower door hole) that would have the same leakage flow rate as the building if both were subjected to a 4 pascal indoor/outdoor pressure difference.
    • Specific leakage area - The Effective leakage area (ELA) divided by the floor area of the conditioned floor area.
    • Leakage at 50Pa / floor area - The air leakage at 50Pa divided by the floor area. This is often used to assess construction and building envelope tightness, because it normalizes the building leakage per unit of floor area.
    • Leakage at 50Pa) / surface area - The air leakage at 50Pa divided by the building surface area. This is often used to assess construction and building envelope tightness, because it normalizes the building leakage per unit of building envelope surface area. Some practitioners include only surface area that is above grade and the resulting metric is sometimes referred to as the Minneapolis leakage ratio (MLR).
    • Leakage coefficient - The building leakage rate when there is an indoor/outdoor pressure difference of 1Pa across the building envelope. This value is typically determined using a multipoint blower door test.

Best practices

Some of the metrics calculated by this tool are used by various codes and standards. For example, the International Energy Conservation Code requires the ACH50 values for the Code years and climates shown in the map and tables below.

IECC airtightness requirements
International Energy Conservation Code tightness requirements
Source: Air Leakage Guide, September 2011. U.S. Department of Energy

Some other published requirements include the Canadian R-2000 Program of 1.5 ACH50 and the Passivhaus Standard of 0.6 ACH50. Also, see the table below for the Energy Star Qualified Homes requirements.

  Energy Star Qualified Homes Version 3 

Climate Zone  ACH50 
 1 - 2  6 
 3 - 4  5 
 5 - 7  4 
 8 3
Source: Energy Star Qualified Homes, Version 3 (Rev. 03) National Program
Requirements (see References below)

Related tools

  • Design Infiltration with AIM-2: This tool calculates the stack-induced, the wind-induced, and the combined infiltration for given indoor/outdoor temperatures and wind speed. The primary use case is determining the design infiltration rate that can be used in a heating or cooling load calculation for system sizing.
  • Advanced Infiltration with AIM-2: This tool calculates the hourly (low, average, and high) stack, wind, and combined infiltration for a selected date range (one day to one year); and the infiltration load on a heating and/or cooling system for the same date range. Additionally, daily average infiltration rates (stack, wind, and combined) and daily infiltration load on heating and cooling systems are displayed on separate charts for a selected TMY3 weather station location and the selected date range.

References

  • ANSI/ASTM E799-10. Standard Test Method for Determining Air Leakage Rate by Fan Pressurization. ASTM International, West Conshohocken, PA.
    Comment: Blower door testing protocol.
  • CAN/CGSB 149.10-M86. Determination for the Airtightness of Building Envelopes by the Fan Depressurization Method. Canadian General Standard Board, Gatineau, Quebec, Canada.
    Comment: Blower door testing protocol.
  • Energy Star. ENERGY STAR Qualified Homes, Version 3 (Rev. 03) National Program Requirements. Effective April 1, 2011.
  • Sherman, M. and Chan, R. Building Airtightnes: Research and Practice. Lawrence Berkeley National Laboratory Report No. LBNL-53356 September 2011.
    Comment: A scholarly overview of airtightenss testing and leakage metrics.
  • U.S. Department of Energy Building Technologies Program Air Leakage Guide. September 2011.
    Comment: A good document keyed to the 2012 version of the International Energy Conservation Code.

Version 2016-07-06_01:30
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