International Energy Conservation Code (IECC) Favors ACH50
The Air Leakage Metrics tool is very helpful for compliance with the tightness levels of the IECC for the last three versions, 2012, 2015, and 2018. Air leakage rates must be five ACH50 or less in climate zones 1 and 2 and three ACH50 or less in climate zones 3 through 8. Refer to the IECC climate zone map below to determine the climate zone within which you are working. How do we know if our blower door value for a residential building complies with the IECC? The RED Air Leakage Metrics tool does the work for you. Because the blower doors give a result in CFM50, but the IECC requires compliance with the metric of ACH50, it is necessary to calculate the equivalent ACH50 for the CFM50 result. The RED tool easily accomplishes this.
Notice in the screenshot of the RED Air Leakage Metrics tool above with detailed house values entered in the top input section of the tool: floor area of 2000ft2, a volume of 16,000ft3, a surface area of 3200ft2, and pressure exponent of 0.65 (default value).
Passive House Institute U.S. Rejects ACH50
The Air Leakage Metrics tool can also help determine if your project is in compliance with the Passive House Institute of the U.S. (PHIUS). In 2015 the PHIUS changed its tightness requirement from 0.6 ACH50 to 0.05 CFM50 per square foot of gross envelope area. Why did PHIUS change this requirement? They had a good reason. PHIUS states on its website:
The Winner for Visualizing Building Leakage is EqLA
A Few Useful Tips
- Click on any input or result label in any RED tool to show the help dialogue for that item. Notice the help dialogue for “Leakage at 50Pa” in the screenshot to the right. These help dialogues explain what you need to know about each of the eight air leakage metrics.
- Click on the blue circle with an “i” inside (upper right corner of any RED tool) to see the User Guide. This resource should answer all your questions about the tool.
- All of the air leakage metrics require values to be entered in the upper section of the tool; some require only “Floor area”, others require all to be entered. For example, if you want to know the equivalent CFM50 for a given ACH50, you must enter the building volume. If you are not seeing the results you want (results are always displayed with a blue font, inputs are displayed with black font), make sure you have entered all the inputs in the top section of the tool.
And Finally . . .
When Charlie and I were designing the Air Leakage Metrics tool, we included all the leakage metrics that were useful AND credible, a total of eight. Notice that Air Changes per Hour (ACH) is not included. Many of you remember the “ACH” included in the BPI Building Analyst Professional Standard, which was used for determining mechanical ventilation for the obsolete ASHRAE 62-1989 Standard; 0.35 ACH. Because this value has no meaningful use any longer, we did not include it as one of the tool metrics. If you are currently using ACH in your work, we recommend you find a substitute.