Duct Blaster vs. Blower Door: When to Use Which—And How to Use Both Better

If you're serious about building performance, you need both weapons in your arsenal: the duct blaster and the blower door.

But when do you use one over the other? And how can you squeeze maximum value out of each test?

Let’s break it down so you can work faster, test smarter, and bill like a pro.

The Blower Door: Test the Whole House

The blower door system is designed to test the entire building envelope. That means it finds leaks in walls, windows, floors, ceilings—everywhere air escapes or infiltrates.

• Primary Use: Whole-house air leakage measurement (ACH50)
• Required For: IECC code compliance, Energy Star, HERS ratings
• When to Deploy: Before insulation, after drywall, and during retrofits

It creates negative pressure, exaggerates the leaks, and lets you prove performance—or spot failures—fast.

The Duct Blaster: Target the HVAC System

The duct blaster (aka duct tester) zeroes in on leakage within the ductwork itself.

This is critical in new builds and retrofits, especially where ducts run through unconditioned space or tight plenums.

• Primary Use: Measuring duct leakage to outside (CFM25 or CFM50)
• Required For: IECC compliance, California Title 24, ENERGY STAR HVAC installs
• When to Deploy: After mechanical is trimmed out, but before final finishes

Connect it at the return. Seal the supply vents (we recommend reusable Vent Caps. Run, get your numbers. Done.

Using Both: The Real Pro Move

When you run a blower door and a duct blaster together, you unlock advanced diagnostics:

• Pinpoint whether leakage is in the building shell or the duct system
• Verify HVAC sealing quality before commissioning
• Build trust with clients through clear, visual proof

And if you’re a HERS rater, RESNET/BPI pro, or energy consultant, having both systems means you never have to say “I’ll come back later.”

Bundle It and Save

At Vent Cap Systems, we offer exclusive discounted bundles for pros who buy both:

• Get a free MiniPack with duct tester or Duct Blaster purchase – Add value and tools to your duct testing setup
• Get a free Total Home Pack with blower door purchase and complete the seal

The Bottom Line

If you’re only using one of these tools, you’re missing out—on diagnostics, credibility, and revenue.

Use the blower door to test the house. Use the duct blaster to test the system. Use both to elevate your business.