Case Study: Sealing Both Systems in a Two-Story Home Nearly Doubled Airflow
If your home has one system upstairs and another downstairs, both can leak, and both can leave rooms short on air. This case study covers a Bay Area home where MaxSeal sealed both systems, jobs H-03 and H-13. Combined leakage dropped from 1,034 to 172 CFM25, and register airflow rose 93%, from 1,371 to 2,647 CFM (cubic feet per minute). Here’s what the tests showed and what it means if your home has two systems.
Key Takeaways
| Common Question | Short Answer |
|---|---|
| How much did leakage drop in this home? | Combined leakage fell from 1,034 to 172 CFM25, an 83% reduction across both systems. How to read the numbers |
| How much more air reached the rooms? | Total register airflow rose from 1,371 to 2,647 CFM, an increase of 1,276 CFM or 93%. |
| Which system improved more? | The downstairs system doubled its airflow, from 876 to 1,752 CFM. Upstairs rose 81%, from 495 to 895 CFM. |
| Do both systems need sealing? | Only if both leak. We test each system separately, so you can see the numbers for each before deciding. Book a test |
| Is there a discount for sealing two systems? | MaxSeal’s Aeroseal sealing is $3,000–$3,500 per system, and multi-system discounts are available. See our price list |
| How does this compare to other homes? | Both systems started in the 450–650 CFM25 range, where our systems gained 64% on average. See all results |
1. The Starting Point
Both systems were leaking heavily. Leakage is measured in CFM25, the cubic feet per minute of air escaping when the ducts are held at 25 Pascals of pressure. Each system was tested separately.
| System | Duct leakage (CFM25) | Register airflow (CFM) |
|---|---|---|
| Upstairs (H-03) | 469 | 495 |
| Downstairs (H-13) | 565 | 876 |
| Combined | 1,034 | 1,371 |
Together, the two systems were leaking over 1,000 CFM25.
2. What the Tests Showed
Both systems fell in the severe range on MaxSeal’s working guide, with more than 400 CFM25 of leakage each. In homes like this, the usual pattern is uneven temperatures between floors, with rooms at the end of long runs getting the least air.
In a two-system home, leaks in one system can make the other look like the problem. If upstairs feels warm, it’s easy to blame the upstairs unit. Testing both systems shows where the air is actually going. Here, both systems had significant leakage, so both were sealed.
3. What We Did
We sealed each system as its own job, with a baseline test, sealing and a final test for each one.
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.
Sealing usually takes one day per system.
4. The Results
| System | Leakage before → after (CFM25) | Leakage reduction | Airflow before → after (CFM) | Airflow change | Theoretical runtime reduction |
|---|---|---|---|---|---|
| Upstairs (H-03) | 469 → 92 | 80% | 495 → 895 | +400 CFM (+81%) | ~45% |
| Downstairs (H-13) | 565 → 80 | 86% | 876 → 1,752 | +876 CFM (+100%) | ~50% |
| Combined | 1,034 → 172 | 83% | 1,371 → 2,647 | +1,276 CFM (+93%) | ~48% |
The runtime figures use the formula 1 − (airflow before ÷ airflow after). For downstairs, that’s 1 − 876 ÷ 1,752, or 50%. For upstairs, 1 − 495 ÷ 895, about 45%. Combined, 1 − 1,371 ÷ 2,647, about 48%. These show how much less time each system would need to deliver the same air, in theory. Real energy savings depend on equipment, settings and weather, and results vary.
Both systems finished above MaxSeal’s standard target of under 50 CFM25, yet each cut its leakage by 80% or more and gained a large amount of airflow.
5. What This Means for Similar Homes
| Upstairs (H-03) | Downstairs (H-13) | Systems starting at 450–650 CFM25 | All 38 systems | |
|---|---|---|---|---|
| Leakage reduction | 80% | 86% | 88% average | 86% average |
| Airflow gain | +81% | +100% | +64% average, +47% median | +47% average, +38% median |
| Airflow added | +400 CFM | +876 CFM | +291 CFM average | +225 CFM average |
Both systems gained more airflow than average for their leakage range. If your home has two systems and some rooms never feel right, test both. One may need sealing and the other may not, or both may, as in this home. Sealing both at once can also qualify for a multi-system discount.
Conclusion
This home’s two systems were leaking a combined 1,034 CFM25. After sealing, leakage fell 83% to 172 CFM25, and register airflow rose 93%, from 1,371 to 2,647 CFM. The downstairs system doubled its airflow.
Your results will depend on your own ducts, but every one of the 38 systems in our data gained airflow. A test of each system is the place to start.
Get a Free Consultation or call (408) 400-3630.
Related: Three-system home case study · 182% more airflow case study · Aeroseal results study · Price list