Duct Blaster® 101: How to Read Your Utah Home’s Duct Leakage Report

If you’ve heard “your ducts are leaky” but haven’t seen the data, this guide shows exactly how to read a Duct Blaster® report—what CFM25 means, how to gauge pass/fail targets, and when sealing with Aeroseal duct sealing makes sense. (Spoiler: real-world homes often see dramatic leakage reductions after sealing.)

First, the basics

• Test pressure: Duct leakage is measured at a standard 25 Pascals (0.10 in. w.c.).
• Units: Results are reported as CFM25—cubic feet per minute of air escaping at 25 Pa.
• Two common tests:
  • Total duct leakage (entire system, regardless of where the air goes).
  • Leakage to outdoors (air that actually escapes the home’s thermal boundary).

How to read your report (step by step)

1. Find the raw number: Look for the pre-test CFM25 value. That’s your baseline leakage.
2. Normalize it: Divide CFM25 by your home’s conditioned floor area and multiply by 100 to get CFM25 per 100 sq ft. This helps compare across different home sizes.
3. Compare to targets: New-construction codes commonly target ≤ 4 CFM25 per 100 sq ft for total leakage at post-construction (jurisdictions vary). Existing homes aren’t required to meet that, but it’s a useful benchmark for “tight.”
4. Look for pre/post: If you sealed the ducts, your report should include a post-test. The difference is your verified improvement.

What counts as “good” for Utah homes?

Rules of thumb (existing homes vary by age/duct location—attics are usually leakier):

• ≤ 4 CFM25/100 sq ft: Excellent/tight (often new builds or well-sealed systems).
• 5–10 CFM25/100 sq ft: Typical for decent systems; comfort can still improve.
• 10–20+ CFM25/100 sq ft: Leaky; expect hot/cold rooms and higher bills. Strong Aeroseal candidate.

Note: Code thresholds and test type (total vs. outdoors) differ by jurisdiction and build stage. We’ll explain which applies to your situation and provide documentation.

Why your ducts might leak

• Unsealed seams at takeoffs, boots, and plenum joints
• Old tape/foam failures or flex-duct connections loosening over time
• Remodels and basement finishes that disturb prior connections

How sealing changes the numbers

Inside-the-duct sealing with Aeroseal typically produces a big drop in leakage—often 70–90% reduction—and you’ll see it verified on the post-test certificate. That usually translates to more air reaching rooms, smoother temps, and lower run time.

Test-day checklist (what we do)

1. Inspect & prep: Mask registers, isolate the coil, and set up the calibrated Duct Blaster® fan and gauge.
2. Pre-test: Pressurize the duct system to 25 Pa and record CFM25 baseline (total or outdoors depending on scope).
3. Seal (if needed): We recommend Aeroseal duct sealing when the data shows it will materially improve comfort/efficiency.
4. Post-test & report: Repeat at 25 Pa; deliver a before/after report you can keep for your records or incentives paperwork.

FAQs

Do ducts “inside the envelope” matter?
Yes—leaks still waste airflow and comfort even if some air stays indoors. Also, many Utah systems still require testing depending on layout and code pathway.

Which test is “right”—total or outdoors?
For retrofit decisions, total leakage is the simplest “how leaky is my system?” number. For new homes and some programs, leakage to outdoors may be specified. We can run either (or both) and explain the implications.

Will I feel the difference?
Most homeowners notice better room-to-room balance and quicker heat/cool times once leakage is cut and airflow is delivered where it should be.