Hidden duct leakage rarely manifests with a single symptom, so contractors start by reading the house. They note rooms that stay warmer or cooler than the rest, registers that hiss, and supply air that carries dust or attic smells. They ask when comfort drops, such as after a filter swap, on windy days, or late in the afternoon when attic temperatures rise. Longer run times, higher utility bills, and uneven humidity can point to air loss before it reaches the grille. They also watch for pressure clues like doors that drift, a weak return pull, or a musty back bedroom.
How the checks unfold
- Visual Tracing from Air Handler to Registers
A systematic walkthrough often finds the first evidence without opening a wall. The crew follows the duct path from the air handler outward, inspecting plenums, takeoffs, and branch connections where seams can separate over time. At each boot, they check the gap between the metal and drywall, since that joint can dump supply air into an attic or pull dusty air into the stream. Flexible duct is inspected for crushed sections, loose inner liners, torn jackets, or straps that allow runs to sag until the collars loosen. The metal duct is checked for loose drive cleats, end caps, and dried-out tape. With the blower running, they feel for air movement at suspected joints, mark locations, and compare leakage risk to nearby insulation and framing. They also inspect return platforms and filter slots, because small bypass gaps can mimic a much larger duct leak. If access allows, they peek behind return grilles for disconnected liners and gaps where sheet metal meets framing inside the cavity.
- Quantifying Leaks with Pressure and Flow Testing
After the map is built, contractors measure how much air is actually escaping. A duct blaster can pressurize the duct system to a standard test pressure and report leakage in airflow units, letting them separate minor seepage from a major failure. They also check the supply plenum pressure and total external static pressure to determine whether the blower is encountering additional resistance from collapsed ducts, debris, or closed dampers that can hide leakage. Smoke pencils or fog help pinpoint the exact opening while the ducts are pressurized, making wisps visible at seams, boots, and return boxes. In Peoria, AZ, this step is critical because superheated attic air pulled into the returns can raise indoor temperatures and make cooling feel inconsistent. Contractors may isolate sections with temporary blocks to learn whether the loss is on a trunk, a branch, or a return chase. They listen for rushing air in adjacent cavities, which often indicates a leak dumping supply into a chase or soffit.
- Thermal Imaging and Room-by-Room Diagnostics
Infrared imaging adds another layer when leaks are buried under insulation or tucked in chases. With the system running steadily, a camera can reveal hot streaks along ceiling lines where a boot is leaking into the attic, or a branch run that is losing capacity through a torn jacket. Contractors pair those images with register temperature checks, comparing each room to the supply plenum to see where the biggest drop occurs. They use airflow hoods or anemometers to measure delivered airflow and then compare the results with what the equipment and duct sizing should support. When a room shows low airflow but normal temperature, they suspect a restriction. When temperature and airflow both fall, a disconnected or heavily leaking branch moves to the top of the repair list. They confirm findings by checking room pressures with the doors closed, since pressure spikes can indicate missing return paths that worsen leakage. For hard-to-reach runs between floors, tracer gas or acoustic microphones can narrow the leak zone without demolition.
- Inspecting Hidden Cavities and Structural Pathways
Some of the most damaging duct leaks occur where ducts pass through framing, wall cavities, or between floors, making direct access difficult. Contractors examine attic decking, crawlspace ceilings, and soffits for indirect clues, such as dust trails, insulation displacement, or temperature differences, that suggest air movement behind the surfaces. They remove select grilles and use inspection cameras to view inside wall cavities, looking for loose boots, disconnected branch lines, or gaps around framing penetrations. They also check panned returns that rely on framing cavities, since these often leak at seams or pull unconditioned air from unintended areas. When accessible, they carefully lift the insulation to inspect hidden trunk lines and confirm that the joints remain sealed and mechanically secure. They also evaluate vibration points near the air handler, since constant movement can loosen connections over time. This step helps ensure that no hidden leaks continue to waste airflow and undermine overall system performance.
Final Verification for Long-Term Comfort and Clean Indoor Air Performance
Once leakage points are identified, contractors plan repairs that improve delivery rather than just covering symptoms. They seal major trunk joints and plenum seams first, since those losses waste the most airflow. Boots and takeoffs get sealed with mastic and approved tapes backed by proper fastening, and damaged flexible connections are reattached with collars that grip the inner liner. After sealing, they repeat leakage testing to document improvement and confirm that static pressure stayed within safe limits. They finish by verifying room airflow, checking return pathways, and adjusting fan speed so the system runs steadily and stays clean indoors overall. Read More