- Rooms that are always too hot in summer or too cold in winter often indicate duct leaks near that zone rather than an undersized system.
- Duct pressure testing quantifies leakage before and after sealing — so results are measurable, not estimated.
- Aeroseal injected sealant reaches leaks inside inaccessible duct sections; mastic sealing addresses accessible joints manually.
Rooms with persistent comfort complaints despite a working system
When one room consistently runs 5–8 °F warmer in summer or colder in winter than adjacent spaces, duct leakage near that branch is a leading suspect. Balancing dampers can help, but sealing the leaks recovers energy and often resolves the comfort issue simultaneously.
Dust accumulation at registers or high utility bills
Leaky return ducts draw unconditioned air — and with it, dust — from attics and wall cavities into the supply air stream. Elevated dust at supply registers combined with higher-than-expected utility bills is a reliable indicator of duct system issues.
How ducts leak and where leaks concentrate
Most duct leakage occurs at joints, connections between flex duct and metal collars, and panned-joist returns common in older North Shore construction. Connections made with standard duct tape — not mastic or foil tape — fail over time as the tape adhesive dries and cracks.
Aeroseal vs. manual mastic sealing
Aeroseal introduces a polymer aerosol into pressurized ductwork; particles accumulate and seal leaks up to ¾ inch from the inside without requiring access. Manual mastic sealing uses a fiber-reinforced compound applied to accessible joints. Legendary assesses which approach fits the duct layout and leakage profile before recommending either.
Duct tape — not the right product for ducts
Standard cloth duct tape fails within a few years in attic and crawl space temperature extremes. HVAC-grade mastic or UL-listed foil tape are the correct materials for duct sealing — any other product should be considered temporary at best.
Sealing without post-test verification
Duct sealing that isn't followed by a post-work pressure test provides no confirmation that leakage was actually reduced. Legendary includes pre- and post-sealing measurements so the improvement is documented.
Questions homeowners ask
- How much can duct sealing reduce my utility bills?
- Typical results range from 10–25% reduction in HVAC-related energy use depending on pre-sealing leakage rates. Legendary provides a pre-test leakage measurement so you can estimate the potential savings before committing.
- Is duct sealing disruptive to the home?
- Aeroseal requires sealing all supply and return registers temporarily during the injection process — typically a half-day project. Manual mastic sealing in accessible attic or basement spaces causes minimal disruption. Both are completed in one visit.
- Does duct sealing qualify for ComEd or Nicor rebates?
- Rebate availability for duct sealing varies by program year. Legendary checks current ComEd and Nicor program schedules and advises on any applicable incentives at the time of your estimate.
Editorial provenance
Content by Legendary Service editorial team
Updated:
Methodology
Guidance compares the stated system factors, applicable utility program rules, and the conditions that must be confirmed in the home. Figures are planning ranges, not quotes; Legendary Service provides an upfront flat-rate price after diagnosis.