What Is a Duct Blaster Test?
A duct blaster test measures air leakage in your HVAC duct system. It’s performed using specialized duct blaster equipment. The test involves temporarily sealing off all supply and return registers, connecting a fan (typically at the central return), and creating negative pressure inside the ductwork.
As the fan pulls air through the system, the amount of air is measured by a pressure gauge (called a manometer). The more air coming in (through holes and gaps), the higher the leakage rate.
When Is the Duct Blaster Test Performed?
Testing usually happens in the final stages of construction, after systems are installed and HVAC is trimmed out, but we can also perform rough-in tests if the air handler is already in place. If you’re wondering how much a duct blaster test costs, reach out for a local quote. Our team covers all major markets in the Carolinas.
What’s a Good Duct Leakage Score?
A great score is 3% Leakage to the Outside (LTO). That’s the benchmark set by Duke Energy’s Residential New Construction Program—and it’s how your project qualifies for utility rebates (assuming all other program requirements are met). Here’s a quick breakdown of targets:
North Carolina Code Targets
- 5% Total Leakage (5 CFM25/100 sf)
- 4% Leakage to the Outside (4 CFM25/100 sf) *aligns with Energy Star requirement*
South Carolina Code Targets
- 12% Total Leakage or 8% LTO (post-construction)
- 6% Total Leakage (rough-in)
Duke Energy Rebate Target
- 3% Leakage to the Outside
Airtight Systems (0% LTO)
These are typically achieved in spray-foamed attics or when all ducts are designed to be located inside the thermal envelope.
Total Leakage vs. Leakage to the Outside (LTO)
Total Leakage includes all duct leakage, whether it’s inside the home, between floors, or in crawlspaces and attics. High total leakage means conditioned air isn’t making it where it needs to go, leading to inconsistent temps and unhappy homeowners.
Leakage to the Outside focuses just on the unconditioned spaces (think attics, basements, and crawl spaces). This is the leakage that’s literally costing you money, wasting energy and cutting comfort.
Pro Tip: Design your HVAC to be inside the thermal envelope, for 0% leakage to the outside. Ducts don’t belong in 140 degree attics in the summer!
How to Pass Your Duct Blaster Test the First Time
Want to nail it on the first try? Here are a couple of field-tested strategies that make a big difference:
1. MORE MASTIC
Specifically at flex duct to collar connections. Mastic should be used generously on the metal duct boot BEFORE sliding the inner air liner onto the boot. This provides an extremely strong seal between the flex air liner and the metal boot. A zip tie or tape alone won’t cut it.
2. Seal Around Boots and Boxes
Caulk the gap between supply boots or return boxes and the sheetrock. You’ll have a hard time meeting code without doing this. Duct leakage is typically cut in half with this one single step.
Want more best practices? Check out our blog on wrapping ducts tighter (Christmas in July edition) →
Or watch our field crew in action on SHINE TV! →
What If You Don’t Pass?
Don’t sweat it. Our team of certified field technicians has seen it all (and sealed it all). We’ll help you troubleshoot the issue and recommend cost-effective solutions. We’ll come back for a re-test once the fixes are made.
Ready to Get Started?
Whether you’re aiming for code compliance or trying to maximize energy performance, our Builders Energy Services team is here to help. Looking for a duct blaster test near you? We provide duct leakage testing across North Carolina and South Carolina. Get in touch to schedule your duct blaster test and make sure your next build is sealed tight.
