Duct sealing in Acalanes Ridge, CA that keeps conditioned air inside the house

Where the air goes when ducts are not sealed

Ducts are assembled from many pieces: trunks, branches, fittings, boots and the plenums that connect to the equipment. Every joint is a potential leak. Over time, tape dries out, fasteners loosen and connections separate. The result is conditioned air escaping before it reaches a register, and on the return side, air being pulled in from places you would never choose to breathe from.

Supply leaks and return leaks cause different problems. Supply leaks waste energy and reduce the air reaching rooms, so the system runs longer to satisfy the thermostat. Return leaks draw in air from attics, crawl spaces and garages. That air can carry dust, insulation fibers, moisture and odors into the system. In humid weather, return leaks from a hot attic can also add a large moisture load that the air conditioner has to remove.

A return leak in a hot attic does more than waste energy. It pulls dusty, humid air straight into the system.

The most common leak points are predictable. Connections at the air handler or furnace cabinet, the joints where branches leave the trunk, and the gap where a register boot meets the ceiling or floor are frequent offenders. Panned joist cavities and building framing used as return ducts in older homes are notoriously leaky because they were never designed to be airtight.

Materials make the difference between a repair that lasts and one that fails in a season. We use duct mastic, a thick sealant that stays flexible, on accessible joints and seams, reinforcing larger gaps with mesh. Where tape is appropriate, we use products listed for duct sealing. Standard cloth duct tape is not used for this purpose because its adhesive breaks down under heat and time.

Testing guides the work. Where access and conditions allow, a duct leakage test pressurizes the system and measures how much air escapes. Repeating the test after sealing shows how much was gained. Even when formal testing is not practical, we check pressures and visible leakage so you know what was addressed and what remains.

Some ductwork cannot be reached without opening finished surfaces. We tell you which sections were sealed and which were not accessible, rather than implying the entire system is tight. When ducts are damaged, undersized or crushed, sealing alone will not solve the problem, and our Ductwork Install And Replace service may be the better fit.

Sealing is often paired with insulation on runs that pass through unconditioned spaces, since a sealed but uninsulated duct still loses heat through its walls. All work is quoted at a flat rate before it begins and covered by our written workmanship warranty.

Signs your ducts are leaking

Leaks are hidden, so symptoms are usually the first clue.

How we seal ductwork

The work follows a clear sequence so the results can be measured and explained.

1. Access and inspection

   Accessible ducts in attics, basements and crawl spaces are inspected for leaks and damage.

2. Leakage and pressure checks

   Testing is performed where practical to establish a starting point.

3. Joint and seam sealing

   Mastic and listed tape are applied to joints, seams and fittings.

4. Boot and plenum sealing

   Register boots and equipment connections are sealed to surrounding surfaces.

5. Follow-up measurement

   Leakage or pressure is checked again so the improvement can be documented.

Factors that affect duct sealing

The scope depends on how much of the system can be reached and its condition.

Duct sealing questions