Advanced Infiltration Tool Guide

What this tool does – [Tool]

This tool calculates the hourly infiltration for a selected date range (one day to one year) and the resulting sensible load on a heating and/or cooling system. Daily average infiltration rates (stack, wind, and combined) and daily infiltration load on heating and cooling systems are displayed on separate charts for the selected date range. Additionally, balanced or unbalanced ventilation can be combined with infiltration with the results displayed in a table and on a chart, along with the resulting additional load on the heating and/or cooling system. The tool combines the powerful AIM-2 infiltration model with typical meteorological year data (TMY3 for the US and CWEC for Canada) for over one thousand weather locations in North America. The tool can be used for:

  • Determining the heating and/or sensible cooling infiltration load for the date range selected, annual or otherwise.
  • Disaggregating (separating) the total infiltration for a selected date range into stack-induced and wind-induced infiltration.
  • Determining the energy savings resulting from building air sealing activities (lowering the CFM50 blower door value).
  • Determining the change in infiltration energy load caused by raising or lowering the thermostat setting.
  • Calculating the increase (decrease) in infiltration resulting from clearing trees (planting trees) around a house. This is done by changing the “Building shelter class”.
  • Finding the infiltration impact of an open flue or chimney.
  • Investigating the effect leakage distribution has on infiltration.
  • Determining the impact of whole-building ventilation (balanced and/or unbalanced) has on heating and/or cooling fuel use.
  • Examining the effects and differences of balanced and unbalanced ventilation on airflow through a building during a selected date range.
  • Examining the effects of infiltration and ventilation to determine when infiltration supplies enough fresh are for acceptable indoor air quality, and when it does not.

Calculated values

  • Hourly stack, wind, and total infiltration, and ventilation and infiltration. These values are reported as low, average, and high for the selected date range.
  • Daily average infiltration rates for the selected date range (infiltration chart): stack, wind, and combined values.
  • Daily average ventilation, total infiltration, and combined rates for the selected date range (ventilation & infiltration chart).
  • Infiltration load on the heating system for the selected date range.
  • The additional load on the heating system due to ventilation, for the selected date range.
  • Combined ventilation and infiltration load on the heating system for the selected date range.
  • Infiltration load on the cooling system for the selected date range.
  • The additional load on the cooling system due to ventilation, for the selected date range.
  • Combined ventilation and infiltration load on the cooling system for the selected date range.
  • Daily ventilation and infiltration load on heating and cooling systems (chart) for the selected date range.


  • 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).
  • This tool, based on the AIM-2 infiltration method, is not intended for buildings of more than three stories above grade, or for multi-unit buildings.
  • All the results under the date range selectors are calculated for the date range you select.
  • The low (high) values in the table will most likely be lower (higher) than the lows (highs) in the first chart. This is because the chart plots daily average values, while the table reports hourly values.
  • Use the default percentages for leakage distribution unless you have reason to believe you have more accurate values. The default percentages are dependent on the building height and whether or not the building has a vented crawlspace.
  • Make sure you read the pop-up help for “Terrain category” and “Building shelter class” before making your selection from the drop-downs. Click/touch on the input label to read the pop-up help.
  • Regarding the “Building has open flue/chimney” section inputs:
    • Do not include flues and/or chimneys that are closed, such as fireplaces with tight-fitting dampers.
    • If there are multiple open flues, add their areas and average their heights.
  • Regarding the “Building has a ventilation system” section inputs:
    • This section accommodates balanced and/or unbalanced ventilation. Enter the know flow rates of the whole-building ventilation fans.
    • If the whole-building ventilation fan(s) are automatically controlled to turn on and off, enter the effective ventilation flow rate that results from the intermittent operation.
  • Check “Show infiltration chart” and/or “Show ventilation & infiltration chart” and/or “Show infiltration energy chart” to display the interactive charts. Select the corresponding “Chart units”. The chart values change as tool inputs above it are changed. Please refer to the “Interactive chart use” section below for more information.

Interactive chart use

This tool includes three interactive charts that can be used to display results; it may also be used for educational, sales, and marketing purposes. For example, you can save a chart in one of four different file formats, embed it into a customer report, or print it separately.

Tips for using the interactive charts:

  • Click/touch the series labels in the legend of either chart to turn the corresponding chart data on or off. For example, in the first chart, you can turn on or off the data series for “Stack”, “Wind”, and/or “Total”.
  • Click/touch the menu icon in the upper right corner of the chart to show the choices for printing the chart or downloading it as an image file in PNG, JPEG, PDF, or SVG format. You are free to use the downloaded image in any way, including reports, presentations, websites, as long as the attribution for “Residential Energy Dynamics, LLC” is included.
  • If you save the chart as an SVG file, you can change the title or any other chart element with the use of third-party software. Examples of third-party software include Inkscape (a free version is available) and Adobe Illustrator.


The Alberta Infiltration Model (AIM-2) applies to low-rise (up to three stories) detached, single-family, residential structures. The development of the empirical model began in the 1980s and was more finely developed over the next decade by David Wilson, Iain Walker, Larry Palmiter, Tami Bond, Max Sherman, and others.

For the mathematical model used for this RED Calc Free tool, “over 3400 hours of measured ventilation rates from the test houses at the Alberta Home Heating Research Facility were used to validate the predictions of infiltration rates and to compare the AIM-2 predictions to those of other infiltration models. The AIM-2 model had bias and scatter errors of less than 15% for wind-dominated ventilation, and less than 7% for buoyancy (“stack-effect”) dominated cases.”

Best Practices

Select the weather station closest to the site you are analyzing. If your location is close to a state border, you might find the closest weather station is in another state. The map feature in the Weather Station Data (TMY) tool is helpful for determining this.does