The Importance of HERS Ratings and Airflow Verification for ADU Projects in San Diego

juniortherater
May 6
3 min read

Accessory Dwelling Units (ADUs) are becoming a popular solution for housing needs in San Diego. As homeowners and builders work to add these smaller living spaces, meeting energy efficiency standards is critical. One of the key ways to ensure compliance and improve home performance is through HERS ratings, blower door testing, duct leakage testing, and airflow verification. These services help ADU projects pass inspections and create more comfortable, energy-efficient homes.

Eye-level view of a technician performing blower door testing on a residential home in San Diego — Technician conducting blower door test on ADU in San Diego

What is a HERS Rating and Why It Matters

The Home Energy Rating System (HERS) is a nationally recognized index that measures a home's energy efficiency. A lower HERS score means the home uses less energy compared to a standard new home. For ADU projects in San Diego, achieving a good HERS rating is often required to meet local building codes and pass energy inspections.

HERS ratings matter because they:

Verify energy efficiency: They provide an objective measure of how well the ADU performs in terms of energy use.
Help pass inspections: Many jurisdictions require a HERS verification report before issuing final occupancy permits.
Reduce utility costs: A better rating means lower energy bills for homeowners.
Increase comfort: Efficient homes maintain more consistent temperatures and better indoor air quality.

For example, a San Diego homeowner building an ADU might find that investing in proper insulation and sealing air leaks improves their HERS score by 10 points, which can translate into hundreds of dollars saved annually on energy bills.

The Role of Blower Door Testing

Blower door testing is a diagnostic tool used to measure the airtightness of a building. During the test, a powerful fan is mounted in an exterior door frame to depressurize the home. This process reveals leaks where air escapes or enters the building envelope.

For ADUs, blower door testing helps:

Identify air leaks that reduce energy efficiency.
Ensure compliance with California’s Title 24 energy standards.
Improve indoor comfort by reducing drafts and moisture intrusion.
Support accurate HERS ratings by providing data on building tightness.

In practice, a blower door test might reveal gaps around window frames or poorly sealed attic hatches in an ADU. Fixing these leaks can improve the home’s energy performance and help it pass inspection.

Why Duct Leakage Testing is Essential

Duct leakage testing measures how much air escapes from the ductwork in heating, ventilation, and air conditioning (HVAC) systems. Leaky ducts can waste energy, reduce system efficiency, and cause uneven heating or cooling.

For ADUs in San Diego, duct leakage testing:

Ensures HVAC systems operate efficiently by minimizing air loss.
Improves indoor air quality by preventing contaminants from entering ducts.
Supports accurate airflow verification for balanced ventilation.
Contributes to better HERS scores by reducing energy waste.

For example, a duct leakage test might find that 20% of conditioned air is lost through leaks in an ADU’s duct system. Sealing these leaks can improve comfort and reduce energy bills.

Airflow Verification and Its Impact on Energy Efficiency

Airflow verification checks that HVAC systems deliver the correct amount of air to each room. Proper airflow is crucial for maintaining comfort, controlling humidity, and ensuring efficient operation.

In ADU projects, airflow verification:

Balances heating and cooling to avoid hot or cold spots.
Prevents system overwork by ensuring proper airflow rates.
Supports compliance with energy codes requiring balanced ventilation.
Enhances occupant comfort by maintaining consistent temperatures.

For instance, airflow verification might reveal that a bedroom in an ADU receives only half the required airflow, causing discomfort. Adjusting dampers or registers can fix this issue and improve overall system performance.

How These Services Work Together for ADU Success

HERS ratings, blower door testing, duct leakage testing, and airflow verification are interconnected steps that ensure an ADU meets energy efficiency standards. Together, they:

Provide a clear picture of the home’s energy performance.
Identify areas for improvement before final inspections.
Help builders and homeowners meet San Diego’s strict energy codes.
Increase the value and comfort of the ADU.

A typical process might start with blower door testing to find air leaks, followed by duct leakage testing and airflow verification to optimize HVAC performance. Finally, a HERS rater reviews all data to assign a rating that reflects the home’s efficiency.

Practical Tips for ADU Builders and Homeowners in San Diego

Schedule testing early in the construction process to address issues before finishing work.
Work with certified HERS raters who understand local codes and requirements.
Invest in quality insulation and sealing to improve blower door test results.
Ensure HVAC systems are properly designed and installed for balanced airflow.
Use test results to guide improvements that boost energy efficiency and comfort.