Duct & Envelope Testing is required for new construction and new installs. We recommend this task during all remodels or retrofits that have the opportunity to improve or degrade these values.
Both tests are for air leakage. Duct leakage is looking for the total leakage from both the return and supply side of your HVAC ducts, a typical home of 15+ years old has an air leakage of 25%.
That means a 4 ton AC unit is only getting 3 tons of cooling thru the register vents to you.
The envelope test is how much your home leaks, your Energy Auditor or Technician needs to convert this to ACH50. Which means under the test conditions how many times per hour did all of the air in the house get replaced with outside air (ACH = air changes per hour). The
more times replaced, then the more your HVAC has to run to condition that new air. If it doesn’t get replaced enough, you could get indoor air quality issues. An Energy Auditor can provide the proper guidance and recommendations.