Every cubic metre of air that escapes through a duct seam is air the fan has paid to move and the chiller or boiler has paid to condition. On a typical UK office AHU running 12 hours/day, 20% leakage equates to several thousand pounds a year in wasted utilities — and to a noticeable drop in the supply rate that reaches occupants, undermining the ventilation rate target and worsening CO₂ levels.
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Why leakage matters
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Manual sealing — when it's the right tool
- New-build and accessible plant-room ductwork
- Identified leaks at flanged joints, branch take-offs, damper frames
- Where mastic, butyl tape or replacement gaskets can reach the leak
- Verified by post-seal pressure test to DW/143
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Aeroseal — when ducts are inaccessible
The system isolates a duct section, pressurises it, and injects atomised polymer sealant. The particles travel with the leaking airflow and accumulate at the leak edge until the gap closes. Pre- and post-seal leakage is measured by the system itself, producing a verified report. It works on rectangular and round duct, supply and return, and on grease-cleaned kitchen extract where TR19 compliance has been re-established first.
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What UK projects typically achieve
Aeroseal projects on UK commercial offices typically reduce measured leakage from 25–30% to 3–6% in a single intervention. Manual sealing produces similar results where access permits but takes 3–5× longer per metre of duct and depends heavily on operative skill.
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The IAQ benefit
Sealed ductwork delivers the supply rate that was specified — meaning measured CO₂, TVOC and PM2.5 actually respond to the AHU. Most "the ventilation doesn't work" complaints in older UK offices resolve to a leakage problem, not a plant-capacity problem. Always test leakage before specifying a new AHU.
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Frequently asked questions
What is Aeroseal?
Aeroseal is an aerosolised polymer sealant injected into pressurised ductwork. It travels with the airflow, accumulates at leak points, and seals them from the inside. The system measures pre- and post-seal leakage and produces a verified leak-rate reduction report — typically 80–95% sealed in a single application.
How much does ductwork leakage cost?
Industry data puts typical UK commercial duct leakage at 15–30% of design flow. That translates to a fan running 20–40% over-power to hit the supply rate at the diffusers — paid for as wasted electricity every hour the AHU runs. Sealing pays back in 2–5 years on most office and retail buildings.
When should I use manual sealing instead?
Manual sealing (mastic, foil tape, gaskets at flanges) is appropriate for accessible new-build ductwork and major leak points found by inspection. Aeroseal is the right tool for retrofit on hidden ductwork (ceiling voids, risers, plant decks) where access for hand-sealing is impractical.
Does sealing affect indoor air quality?
Yes — positively. Leaky supply ductwork pulls in ceiling-void air (dust, insulation fibres, occasionally rodent contamination) instead of clean conditioned air. Leaky returns can short-circuit airflow and reduce dilution of CO₂ and VOCs in the occupied space.