Duct leakage is invisible, which is why it is tolerated for years. Nothing drips, nothing alarms, and the house simply becomes slightly less comfortable and slightly more expensive to run. Then one bedroom stops keeping up and somebody finally goes looking.
These are the symptoms, and the places the leaks actually are.
One room that is always off
The most common presentation by far. Everything else in the house is fine, and one room sits several degrees away from the thermostat in both seasons.
Cleaning will not fix this. It means the air intended for that room is going somewhere else, and the usual causes are a branch that has pulled off its boot in a crawlspace, a flex run crushed under attic storage, or a duct that was undersized when the house was built.
Airflow improvement is the single most-mentioned result in our Google reviews, named directly in eleven of them, and this is the symptom behind most of those jobs.
Weak airflow at a register that used to be fine
Different from the room above, because you can feel it at the grille. Hold your hand at a supply that has changed and compare it with one that has not. A clear difference between two registers on the same floor points at that branch, not at the equipment.
A whistle or a rush near the air handler
Air escaping through a gap makes noise. A whistling or rushing sound at the plenum or the first few feet of trunk, especially at start-up, is a seam that is not sealed.
The return side is worse than the supply side for a reason people find counter-intuitive: a leaking return pulls unconditioned air in from wherever it passes through, so a return leaking in a crawlspace is delivering crawlspace air to your bedrooms.
Dust drawn to a joint on exposed ductwork
Look at any visible ductwork in a basement or utility room. If there is a line of dust collecting along a seam, air is moving across it. That is a leak marking itself.
Insulation or debris coming out of a register
Fibreglass strands, dirt or wood chips arriving at a grille mean the run is open to a space it should not be, usually where a boot has separated from the floor or a section has come apart in a crawlspace.
Utility bills climbing with no change in habit
The least specific symptom and the one that finally motivates the call. Every cubic foot of air that leaks out of a supply was heated or cooled by your equipment first, and every cubic foot pulled into a leaking return has to be conditioned from scratch. The equipment compensates by running longer.
Be sceptical of anyone who puts a precise percentage on your house without inspecting it. The honest version is that sealing accessible leaks stops paying to condition space you do not live in, and how much that is worth depends on how leaky it is now.
Where the leaks actually are
In our experience, in this order:
- Boot connections at registers. The joint between the branch and the register boot is frequently unsealed, and floor boots in particular work loose over decades of foot traffic above them.
- Plenum seams at the air handler. The highest-pressure metal in the system, and often the least finished.
- Crushed or disconnected flex in attics. Storage is the enemy. Flex has no memory, so a box left on a run for a decade leaves a permanent restriction.
- Crawlspace runs. Moisture, rodents and time. Insulation sags off, a boot drops, and the branch ends up delivering to the dirt.
- Joints held with duct tape. Which brings its own article, because tape on a duct fails in a specific and predictable way.
What an inspection actually looks at
Attic, crawlspace, basement and any exposed trunk, looking for disconnects, kinks, crushed flex, corroded seams and unsealed joints. Airflow compared register to register so the weak branch is identified rather than guessed at. Then photographs, because nobody should approve work on a duct they have never seen.
Only after that is a repair quoted. That is the process on the repair service page, and the first question it answers is the one worth answering before you spend anything: is this a cleaning problem or a ductwork problem?
