As you may have heard, the RESNET 380 standard will replace RESNET Ch. 8 which dictates how raters test homes for envelope leakage, duct leakage, mechanical ventilation, and duct system air flows. Any home permitted on or after July, 1 2018 must be tested in accordance to the 380 Standard. The standard currently applies to all single-family homes as well as multifamily projects that are three stories or less. There are more updates coming for multifamily so make sure you are signed up to receive email updates from RESNET.


One goal of the 380 standard is to improve consistency throughout the HERS process and to reduce the need for Raters to make judgement calls when taking measurements in the field. To help achieve this, the standard includes definitions for:

  • Conditioned Space Volume
  • Unconditioned Space Volume
  • Infiltration Volume
  • Conditioned Floor Area
  • ELA & other metrics

Envelope Leakage Testing

Another goal of the standard is to provide flexibility by offering various test methods. For blower door testing, both single and multi-point tests are allowed. To make testing and calculations faster and easier, automatic testing software from equipment manufacturers such as the rCloud app is also allowed. One key item to note for single-point testing is blower door leakage readings must be adjusted by adding 10% to the CFM50 or ELA for new homes being tested for a HERS rating. This is a function that rCloud will do automatically when the RESNET 380 test standard is selected in the software.

Duct Leakage Testing

Similar to RESNET Ch. 8, ducts are to be pressurized or depressurized to 25 Pa when tested for leakage. Both total and leakage to outside tests are permitted including the Delta Q method. One key change for testing ducts is a rater cannot connect to a return grille unless there are three or less returns and/or the total duct leakage is < 50 cfm, or local jurisdiction prevents connection to blower access. Otherwise, the DucTester fan will need to be attached at the air handler. You may attach the DucTester fan at the return grille if local codes require you to have a license to remove the air handler access panel or if the air handler is located in an area with limited access.

Mechanical Ventilation Testing

When testing mechanical ventilation, airflow can be measured at the inlet with a powered flow hood, exhaust box, or passive flow hood. It can also be tested at the outlet with a powered flow hood or by using the bag inflation method or in the duct using a flow measurement station which can be a permanent or temporarily installed device.

Total Heating/Cooling System Airflow

RESNET 380 requires raters to measure the total air flow of a heating and/or cooling system. This can be done by pressure matching where the rater will measure the pressure differential from the supply plenum to the home, attach the DucTester fan at the blower access or return grille, then turn on DucTester to match the measured pressure differential. This test can also be done using a calibrated flow plate that can be inserted into the filter slot.

You can watch a video recording of this webinar below. Visit our YouTube page for even more informative videos & stay tuned for more articles from Retrotec to keep you informed on industry news, tips and tricks from the field, and new product updates and releases.

About the Author:

Sam Myers, marketing & training consultant for Retrotec. Prior to joining the Retrotec team, Sam held the role of a Building Science Specialist, where he managed field operations for building performance programs. With Retrotec, he attends many conferences and trade shows, as well as holds specialized webinars and presentations. Sam can also be found out in the field conducting studies and trying out new equipment and techniques.