A Walnut Creek homeowner called about uneven comfort. Front rooms felt right. The back rooms stayed cold in winter and warm in summer, and moving the thermostat did nothing. The equipment was fairly new and ran the way it should, so I did not suspect the furnace or the condenser. The complaint had the signature of a delivery problem, not a production problem.
The crawl space told the real story
I checked the unit first and confirmed it was working. Then I went under the house with a flashlight. That is where the job actually was.
Several duct sections had pulled apart at the joints. Others sagged far enough to pinch the airflow down to a trickle. In at least two spots the flex duct had torn open completely. The system was moving air, but a good share of that conditioned air emptied into the crawl space before it reached the back of the house. Static pressure was off. Airflow was unbalanced. The homeowner had been paying PG&E to heat the dirt under the floor.
This is the most common “the HVAC isn’t working” call that turns out to have nothing to do with the HVAC. Crawl-space ductwork is the part of the system nobody looks at, because you cannot see it without crawling under there.
Mapping every run, then sealing what counts
I mapped each duct run end to end against the equipment outputs, so I knew which register every length of duct was supposed to feed. From there the work was specific.
We repaired and re-supported the disconnected and sagging sections. Joints got resealed with HVAC-grade mastic. I do not use duct tape on duct seams. The adhesive dries out and the tape lets go in roughly 18 months, while mastic stays put for 20 years and more. A few sections of duct material had degraded past patching, so those came out and got replaced rather than nursed along. On the repaired runs we installed fresh R-8 insulation to stop heat from bleeding off into the crawl space.
The detail that made the fix hold
What made this repair stick was finishing it with a pressure test. After the work, I tested the system and confirmed balanced airflow at every register, so nothing was guessed and nothing got signed off on a hunch.
There is a judgment call worth naming here. A lot of contractors will quote a new system before they will quote a duct repair, because the new system is the bigger ticket. The rule I use runs the other way. Rule out duct integrity first. If the ducts leak 30 percent, a new high-efficiency system leaks 30 percent too, and the homeowner spends $15,000 to keep the exact comfort problem they started with. The duct repair on this job cost a fraction of that and fixed the cause.
What the homeowner ended up with
Consistent airflow at every register. Even temperatures room to room. A duct system that should last the rest of the equipment’s service life. The homeowner reported a noticeable drop on the following month’s PG&E statement, and the repair is covered by our 1-year warranty.
If your rooms heat and cool unevenly and the system itself seems fine, the ducts are the first place I look. You can read more about how we approach this on our ductwork and HVAC repair work, handled through our HVAC division, Bay Area HVAC Service.
