Leaky ducts can deliver less conditioned air to occupied rooms or pull unwanted air into the return system. A room that never feels comfortable, unexplained dust, or a high bill can justify an assessment. None of those symptoms proves a duct leak by itself. Insulation, windows, equipment settings, and airflow restrictions can produce similar complaints.
Supply and return leaks have different effects
Supply ducts carry air from the equipment toward rooms. A leak into an unconditioned attic may send useful cooling or heat outside the intended space. Return ducts bring air back. Leakage there can draw attic or crawl-space air into the system before it reaches the equipment. The DOE duct-improvement checklist identifies added moisture and pollutants among the concerns with returns in unconditioned areas.
Location matters. A leak inside the conditioned enclosure does not have the same consequences as one into a hot attic. It may still impair room delivery or pressure balance. Ask the contractor to distinguish total leakage from leakage to outside the conditioned space, and to explain the test method used.
Avoid the “30 percent off your bill” shortcut
ENERGY STAR describes typical duct losses of roughly 20–30 percent of the air moving through a duct system. That general statement is not a measurement of your house and is not a promise of 20–30 percent whole-house utility savings. Air leakage, delivered heating or cooling, equipment input, and total household energy are different quantities.
Here is an intentionally simplified example. Assume your household spends $2,400 annually on energy, of which $1,200 is attributed to heating and cooling. If a project truly reduced that HVAC portion by 10 percent, savings would be $120, or 5 percent of the whole bill. The 10 percent assumption is illustrative and is not inferred from a leakage test. This calculation shows why the denominator matters.
What to record before the assessment
Make a room-by-room list: which spaces are uncomfortable, what time of day it happens, whether doors are open, and whether the problem occurs in heating, cooling, or both. Save bills with usage in kWh or therms and the billed rates. A higher dollar amount alone can reflect a rate change.
From normal occupied areas, note furniture covering registers and whether returns are unobstructed. Do not enter a hazardous crawl space or touch damaged insulation to collect evidence. Photos of accessible disconnected or crushed ducts are useful, but the absence of visible damage does not rule out leakage.
| Observation | Question for the assessor |
|---|---|
| Room improves when its door is open | Is there an adequate return-air path? |
| Problem began after attic work | Were ducts disconnected, crushed, or disturbed? |
| Dust appears near a return | Is the return enclosure sealed, and is the filter fitting correctly? |
| Weak airflow at one register | Is the branch restricted, leaking, or improperly balanced? |
| Humidity rises during operation | Are return leaks or drainage problems contributing? |
What a useful repair proposal includes
Request a sketch or description of the affected branches, the material and condition of the ducts, and the diagnostic findings. The DOE checklist calls for inspection, pre- and post-work leakage testing, and airflow verification. Ask that the final report contain actual results rather than a checkmark labeled “tested.”
Separate sealing, damaged-section repair, insulation, and airflow correction in the price. They solve related but different problems. An intact leaking joint may be a sealing candidate; a collapsed flexible branch may need physical replacement before sealing can help.
How to judge the result
Agree on the acceptance measurements before work starts: leakage target and method, airflow at problem rooms, and restoration of insulation and access. Afterward, compare comfort under similar weather and door conditions. Weather-adjusted energy analysis is more informative than comparing one mild month against one severe month.
Use our sealing-versus-replacement guide to organize competing proposals. The best scope addresses the measured defect and verifies the result; it does not promise a universal saving based on the age of the ducts.