Case Study: Three Systems, One Home, 92% Less Duct Leakage
If your home has several HVAC systems, each one can leak differently and gain differently from sealing. This case study covers a Bay Area home with three systems serving the bedroom wing, the kitchen area and the garage side, jobs M-04, M-11 and M-15. Combined leakage dropped from 962 to 81 CFM25, a 92% reduction, and register airflow rose 42%. All three finished at 30 CFM25 or lower. Here’s why the gains weren’t equal.
Key Takeaways
| Common Question | Short Answer |
|---|---|
| How much did leakage drop across the home? | Combined leakage fell from 962 to 81 CFM25, a 92% reduction. How to read the numbers |
| How tight did the systems get? | All three finished at 30 CFM25 or lower, which is excellent for a home system. Duct sealing glossary |
| How much more air reached the rooms? | Total register airflow rose from 1,154 to 1,633 CFM, an increase of 479 CFM or 42%. |
| Why did one system gain 79% and another 22%? | Systems that delivered less air before sealing had more room to improve. The kitchen system was already delivering the most air. See all results |
| Do I need to seal every system in my home? | Not always. We test each system separately so you can decide based on the numbers. Book a test |
| What does sealing three systems cost? | Aeroseal sealing is $3,000–$3,500 per system, and multi-system discounts are available. See our price list |
1. The Starting Point
All three systems had moderate to high leakage. Leakage is measured in CFM25, the cubic feet per minute of air escaping when the ducts are held at 25 Pascals of pressure.
| System | Duct leakage (CFM25) | Register airflow (CFM) |
|---|---|---|
| Bedroom wing (M-04) | 292 | 307 |
| Kitchen (M-11) | 329 | 566 |
| Garage side (M-15) | 341 | 281 |
| Combined | 962 | 1,154 |
The leakage numbers were fairly similar, between 292 and 341 CFM25. The airflow numbers were not. The kitchen system was delivering about twice as much air as the garage-side system.
2. What the Tests Showed
All three systems fell in the leaky range on MaxSeal’s working guide, between 150 and 400 CFM25. In homes with numbers like these, the usual pattern is noticeable comfort differences, with rooms at the end of long runs getting the least air.
The airflow readings told a more useful story than leakage alone. The bedroom wing and garage-side systems were each delivering around 300 CFM or less. The kitchen system was delivering 566 CFM. That difference turned out to predict which systems would gain the most.
3. What We Did
Each system was sealed as its own job, with a baseline test, sealing and a final test.
Our Typical Aeroseal Process
- Baseline test. Measure leakage with a calibrated Retrotec fan and airflow at every register with a flow hood.
- Hand repair. Fix any gaps too large for Aeroseal, which seals holes up to about 5/8 inch.
- Prepare the system. Block the registers and isolate the furnace and coil so sealant only builds at the leaks.
- Seal. Inject the Aeroseal sealant while a computer tracks leakage live.
- Final test and report. Retest leakage and airflow and provide a before and after report for each system.
4. The Results
| System | Leakage before → after (CFM25) | Leakage reduction | Airflow before → after (CFM) | Airflow change | Theoretical runtime reduction |
|---|---|---|---|---|---|
| Bedroom wing (M-04) | 292 → 30 | 90% | 307 → 437 | +130 CFM (+42%) | ~30% |
| Kitchen (M-11) | 329 → 28 | 91% | 566 → 692 | +126 CFM (+22%) | ~18% |
| Garage side (M-15) | 341 → 23 | 93% | 281 → 504 | +223 CFM (+79%) | ~44% |
| Combined | 962 → 81 | 92% | 1,154 → 1,633 | +479 CFM (+42%) | ~29% |
All three systems beat MaxSeal’s standard target of under 50 CFM25. Two finished under 30, and the bedroom wing finished at 30.
The runtime figures use the formula 1 − (airflow before ÷ airflow after). For the garage side, that’s 1 − 281 ÷ 504, about 44%. For the kitchen, 1 − 566 ÷ 692, about 18%. Combined, 1 − 1,154 ÷ 1,633, about 29%. These are theoretical, and real savings depend on equipment, settings and weather.
5. What This Means for Similar Homes
The three systems ended up with nearly identical leakage, yet their airflow gains ranged from 22% to 79%. The difference comes down to the starting airflow. The garage-side system delivered the least air before sealing and gained the most. The kitchen system was already delivering the most and gained the least.
| This home (combined) | Systems starting at 250–450 CFM25 | All 38 systems | |
|---|---|---|---|
| Leakage reduction | 92% | 85% average | 86% average |
| Airflow gain | +42% | +36% average, +33% median | +47% average, +38% median |
| Airflow added | +479 CFM total | +182 CFM average per system | +225 CFM average per system |
That matches the wider data. Systems delivering under 400 CFM before sealing gained a median 38%, while those delivering 700 CFM or more gained a median 22%. If you’re deciding which system to seal first, the one with the weakest airflow is often the one with the most to gain. After sealing, the new readings can also show where register or damper adjustments would help.
Conclusion
This home’s three systems leaked a combined 962 CFM25. After sealing, leakage fell 92% to 81 CFM25, every system finished at 30 CFM25 or lower, and register airflow rose 42% overall.
The gains differed because the starting airflow differed. Testing each system shows which ones leak, which ones are starved for air, and where sealing will make the biggest difference.
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Related: Two-system home case study · 182% more airflow case study · Aeroseal results study · Air balancing vs. duct sealing