Blower door testing in Tennessee must comply with the 2018 International Energy Conservation Code (IECC), which requires residential buildings to achieve an air leakage rate of 3 ACH50 or less. Testing protocols follow the ANSI/RESNET/ICC 380 standard, which governs equipment calibration, testing procedures, and documentation requirements.
At Middle Tennessee Blower Door, every test we perform adheres to these national standards. As a RESNET certified energy rater with over 20 years of construction experience, Chris Lewis ensures your documentation meets the requirements that building inspectors across Nashville, Franklin, Murfreesboro, and throughout Middle Tennessee expect to see.
Tennessee adopted the 2018 International Energy Conservation Code (IECC) with state-specific amendments for residential construction, effective July 16, 2020. This applies to one and two-family dwellings and townhouses throughout the state. Tennessee is a home rule state, meaning codes are enforced at the local jurisdiction level, but the 2018 IECC serves as the statewide minimum standard.
The State Fire Marshal's Office oversees building code enforcement, and any new residential construction project requiring a permit must demonstrate compliance with these energy efficiency requirements before receiving a certificate of occupancy.
The 2018 IECC establishes specific air leakage limits based on climate zone. Tennessee falls primarily within Climate Zones 4A and 3A, which require a maximum air leakage rate of 3 ACH50, meaning no more than 3 air changes per hour when the building is pressurized or depressurized to 50 Pascals.
Tennessee IECC 2018 Air Leakage Requirements:
Requirement
Standard
What It Means
Maximum Air Leakage
3 ACH50
3 complete air changes per hour at 50 Pascals pressure
Test Pressure
50 Pascals (0.2 in. w.g.)
Standard pressure differential simulating worst-case conditions
Testing Protocol
RESNET/ICC 380 or ASTM E779
Approved national standards for test procedures
Documentation
Written signed report
Results must be provided to building official
For context, the previous 2009 IECC allowed up to 7 ACH50, meaning current standards are more than twice as stringent. This reflects the building industry's improved understanding of how air leakage affects energy efficiency, comfort, and indoor air quality.
RESNET, the Residential Energy Services Network, is a national nonprofit organization that establishes standards for energy efficiency ratings and inspections in residential buildings. When you work with a RESNET certified rater, you are working with someone who has completed rigorous training, passed national examinations, and maintains ongoing quality assurance requirements.
RESNET certification requires:
Completion of HERS Rater training and supervised field ratings
Passing the National Rater Core Exam
Passing the RESNET Practical Simulation Exam
Passing the National Rater Combustion Safety Simulation Exam
Ongoing contract with a RESNET Quality Assurance Provider
Completion of probationary ratings under supervision
This certification matters because building inspectors across Middle Tennessee recognize RESNET credentials as meeting the "approved third party" requirement that many jurisdictions now require for blower door testing. Your test results carry the credibility that code officials expect.
The ANSI/RESNET/ICC 380 standard is the American National Standard for testing airtightness of building enclosures, duct systems, and mechanical ventilation systems. Developed jointly by RESNET and the International Code Council (ICC), this standard provides the detailed procedures that testers must follow to produce accurate, consistent, and legally defensible results.
The 380 standard specifies:
Equipment calibration requirements and acceptable tolerances
Building preparation procedures before testing
Test pressure requirements and measurement protocols
Calculation methods for air leakage rates
Documentation and reporting requirements
Quality assurance procedures
The standard allows for both single-point and multi-point testing methods, providing flexibility while maintaining accuracy. It also includes specific procedures for testing attached dwellings like townhouses and duplexes, where shared walls create unique testing challenges.
ACH50 stands for Air Changes per Hour at 50 Pascals. This measurement tells you how many times the entire volume of air inside your home would be replaced with outside air in one hour if the building were held at the test pressure of 50 Pascals.
The calculation formula is: ACH50 = (CFM50 x 60) / House Volume
Where CFM50 is the cubic feet per minute of air flowing through the blower door fan at 50 Pascals, and house volume is the total cubic footage of the conditioned space. A lower ACH50 number indicates a tighter building envelope with less air leakage.
For example, a 2,000 square foot home with 9-foot ceilings has a volume of 18,000 cubic feet. If the blower door measures 900 CFM50, the calculation would be: (900 x 60) / 18,000 = 3.0 ACH50, which would exactly meet the Tennessee code requirement.
When ductwork runs through unconditioned spaces like attics, crawlspaces, or garages, the 2018 IECC also requires duct leakage testing. The standard requires total duct leakage of no more than 4 CFM per 100 square feet of conditioned floor area, or leakage to outside of no more than 4 CFM per 100 square feet.
Duct testing uses similar equipment to blower door testing but measures air leakage from the HVAC distribution system rather than the building envelope. The ANSI/RESNET/ICC 380 standard covers duct leakage testing procedures as well, ensuring consistent methodology across both tests.
Middle Tennessee Blower Door provides both blower door and duct leakage testing services, allowing builders to get complete code compliance documentation from a single visit.
The Tennessee State Fire Marshal's Office has been working toward adoption of the 2021 building codes, including updates to energy efficiency requirements. While implementation has faced delays, builders should be aware that updated standards are on the horizon. The 2021 IECC maintains the 3 ACH50 requirement for most residential buildings but includes additional provisions for multi-family and attached dwelling units.
The trend nationally is toward increasingly stringent air leakage requirements. The original 2009 IECC allowed 7 ACH50, the current 2018 IECC requires 3 ACH50, and some voluntary programs like Passive House require 0.6 ACH50 or less. Building tight from the start positions your projects well for both current requirements and future standards.
Code compliance is the minimum requirement to obtain a certificate of occupancy, but the standards behind blower door testing serve broader purposes. Proper air sealing reduces energy costs, improves indoor comfort by eliminating drafts and hot spots, prevents moisture problems that can lead to mold and structural damage, and improves indoor air quality by controlling where air enters the building.
When your testing is performed by a certified professional following established standards, you get more than a pass or fail result. You get documentation that stands up to inspection, actionable information about where problems exist if remediation is needed, and confidence that your building performs as intended.
Every blower door test we perform follows IECC requirements and RESNET protocols. Your documentation meets the standards that building officials across Davidson, Williamson, Rutherford, Sumner, Wilson, and surrounding counties expect. Same-day results, professional reporting, and the technical expertise to help identify and resolve issues when they arise.