No single gap looks serious. A typical system has dozens of joints, and a few hundredths of a square inch at each can add up to a leak the size of a window. The loss is a share of everything the blower delivers.
Service · Alhambra, CA
Duct Sealing and Leakage in Alhambra, CA
Duct leakage can be measured, and the measurement is what turns a hopeful repair into a verified one. A pressurized test reports how much air escapes, sealing with the right materials closes the gaps, and a second test confirms that it worked.
What you are seeing
When sealing and testing make sense
- Sound ducts, high losses
The runs are intact but joints leak across the system.
- Permit requirement
A replacement or alteration needs verified leakage.
- Comfort complaints
The house runs long without reaching the setpoint.
- Before new equipment
Leaks are closed so the new system is not wasted on the attic.
How it works
How small gaps add up
Leakage is expressed as a percentage of the blower's airflow, which is why a test with instruments, rather than a look by eye, is the only way to know.
- Total leakage
Air lost anywhere in the system, to the attic or the outdoors.
- Leakage to outside
Air lost to unconditioned space only, which matters most for energy loss.
- Return leakage
Attic air drawn in, which adds dust and heat to the coil.
Property type
Why older Alhambra systems leak at the seams
Ducts from earlier decades were sealed with cloth tape, which dries and peels in attic heat. Even careful work done under older practice leaves seams that modern testing exposes.
- Cloth tape
Loses adhesion within a few summers.
- Foil tape
Peels at corners when the adhesive ages.
- Unsealed seams
Plenums and trunks built before sealing was required.
Technique
How a leakage test and sealing proceed
Seal the registers
Temporary covers are placed over every grille.
Pressurize
A calibrated fan raises the duct pressure to a set test value.
Read the flow
The airflow needed to hold that pressure is the leakage.
Find the gaps
Fog, smoke or hand feel locates the biggest leaks.
Seal with mastic
Joints and seams receive a brushed layer of mastic, with mesh for wide gaps.
Retest
The pressure test is repeated after the mastic cures.
Describe why you want the ducts tested and whether work is planned, and the call can say how the test fits.
(626) 687-0603Phase order
Baseline, seal, cure, verify
The first test shows how much leakage exists. The sealing follows, and the second test cannot be run until the mastic has cured. The difference between the two numbers is the improvement.
Triage order
Why mastic is preferred over tape
- Mastic
A paste that cures into a flexible, durable seal.
- Listed tape
Approved foil tapes can be used, but only when applied to clean, dry metal.
- Cloth tape
Fails in heat and is not an accepted seal.
- Mesh
Wide gaps are bridged with fiberglass mesh and then coated.
Local detail
Testing in a hot Alhambra attic
Leakage tests are easier on a day when the attic is not at its peak, so Alhambra crews often schedule them in the morning or in cooler months. Los Angeles County homeowners should expect the attic to be hot even then.
Measured results
What the verification test records
- Total leakage
The measured percentage is within the Title 24 limit.
- Airflow
The system moves its rated volume across the coil.
- Report
The rater files the result so the permit can close.
Documentation
Raters, permits and Title 24 verification
California's Title 24 requires third-party verification of duct leakage on many replacements and alterations. The technician files the permit with the City of Alhambra Building Division, and the rater is independent of the installer.
Ask who arranges the rater and when the retest takes place. Scope and pricing are set directly with the independent technician.
Safety protocol
Preparing the house for a leakage test
- Clear the registers
Furniture and rugs should not block any grille.
- Expect covers
Temporary covers sit over every register for the duration of the test.
- Keep pets away
The test fan is loud and the attic access is open.
Scope: Emergency diagnostic dispatch, whole system replacement and ductwork replacement only. Scope and pricing are provided directly by independent licensed contractors.
Common questions
Questions about duct sealing and testing in Alhambra
Is duct testing available in 91801, 91803 and 91804?
This guidance covers Alhambra homes in ZIP codes 91801, 91803 and 91804.
What does a duct leakage test measure?
It measures the airflow needed to hold a set pressure in the sealed duct system, which equals the air that leaks.
Why does mastic last longer than tape?
Mastic cures into a flexible coating that holds its grip through heat swings. Cloth tape dries and peels.
Who performs the Title 24 verification?
An independent third-party rater, separate from the installing technician, performs and files the test.
A heating or cooling fault rarely fixes itself.
Call and describe the problem in Alhambra: what the system is doing, what it did first and how old the equipment is.