Duct Sealing in Sunnyvale: Better Airflow for Ranch Homes, Additions and ADUs

Key Takeaways

1. Why Ducts Matter in Sunnyvale Homes

Sunnyvale grew quickly after World War II. Census counts show about 9,800 residents in 1950, about 52,900 in 1960 and about 95,400 in 1970, as farmland and orchards turned into neighborhoods. That means a large share of the city's single-family homes came out of the same postwar building boom.

Many of those homes were built for heating, and air conditioning or a heat pump came later on the original ducts. Decades on, joints loosen, flex duct sags and tape dries out. ENERGY STAR estimates a typical home loses 20–30% of the air moving through its ducts, and the rooms farthest from the equipment feel it first.

2. Eichlers: Check for Ducts First

Sunnyvale has one of the largest concentrations of Eichler homes, with more than 1,000 by most counts. Many Eichlers were built on concrete slabs with radiant heat, where hot water runs through tubing in the floor and there is no ductwork. If your Eichler still heats only that way, or cools with ductless mini-splits, Aeroseal doesn't apply, and we'll tell you so.

Some owners have added a ducted system later, often routed through the attic, the roofline or the garage. Those ducts can leak like any others and can be tested and sealed. A free video consultation usually settles whether your home is a fit.

3. Signs Your Ducts Are Leaking

• A back bedroom or the room over an addition never matches the thermostat
• Upstairs runs warm after a second-story addition
• Some registers blow hard while others barely move air
• Dust builds up quickly, even with a good filter
• Ducts run through an attic, crawl space or garage
• A new AC or heat pump feels weaker than expected

A duct leakage and airflow test measures the leakage and the air reaching each room.

4. Additions, Second Stories and ADUs

Sunnyvale homeowners have added on for decades. A family room addition, a second story or a backyard ADU usually means new duct runs tied into old ones, and those connections are where leaks often start.

In our Bay Area data, one ADU system (M-08) went from 320 to 34 CFM25 and gained 24% airflow. CFM25 means cubic feet per minute of leakage at 25 Pascals of pressure.

5. Townhomes and Two-System Homes

If you live in a townhome with its own furnace, air handler or heat pump, your ducts can be tested and sealed like any house. We work only on your unit's system, and we'll tell you if anything appears to connect to a shared building system. Check your HOA's rules on contractor access.

Larger homes and homes with a second-story addition sometimes have two systems. We test and report each one separately, and multi-system discounts apply. In one two-system home from our Bay Area data, the upstairs system (H-03) went from 469 to 92 CFM25 and gained 81% airflow, while the downstairs system (H-13) gained 100%. See the two-system case study.

6. How Aeroseal Seals Without Opening Walls

Most duct leaks hide inside walls, floors and ceilings. Aeroseal reaches them from the inside. We block every register, isolate the furnace and coil, pressurize the ducts and blow in a fine sealant mist. The particles stay airborne until they reach a leak, then build up at its edges until it closes.

Aeroseal seals gaps up to about 5/8 inch, so larger ones get hand-repaired first.

Our Typical Aeroseal Duct Repair Process

1. Free consultation. At your home or by video.
2. Baseline test. A calibrated Retrotec fan measures leakage in CFM25, and a flow hood reads every register.
3. Hand repair. We reconnect separated joints, replace crushed flex duct and close gaps over 5/8 inch.
4. Aeroseal sealing. A computer tracks leakage falling in real time. Aeroseal recommends occupants are out during this stage.
5. Final test and report. You get before and after leakage and airflow in writing.

Most jobs are done in a few hours. Read how it works.

7. What Changes After Sealing: Bay Area Data

These are MaxSeal's Bay Area-wide averages from 38 sealed systems. They are not Sunnyvale results.

In theory, a 38% airflow gain means about 28% less runtime for the same delivered air. Results vary by home. See our results study.

8. Heat Pumps, Smoke Season and Title 24

If you're swapping a furnace for a heat pump, the ducts will carry cooler supply air. Heat lost through leaks makes it feel cool at the register, which people call cold blow. California's Title 24 generally requires a duct leakage test with third-party HERS verification when equipment is replaced, so confirm the target with your contractor or building department. MaxSeal works on ducts only, so we have no equipment to sell.

During wildfire smoke season, sealed return ducts pull less unfiltered attic and crawl space air into the system, so more of your indoor air passes through the filter. See heat pump cold blow and air quality.