Quick answer
What is the difference between thermal and acoustic ductwork insulation?
Thermal ductwork insulation limits heat gain or loss between the air in the duct and the surrounding space, and stops condensation on chilled-air runs. Acoustic insulation reduces noise transmission from fans and the duct itself. Supply, extract and chilled-air duties each call for a different combination of the two.
What does thermal ductwork insulation do?
Thermal insulation keeps the air inside the duct close to the temperature it was delivered at. On a heating duct it limits heat loss; on a chilled-air duct it limits heat gain and, crucially, stops condensation forming on the outside. The finish must include a sealed vapour barrier on cold runs.
What does acoustic ductwork insulation do?
Acoustic insulation reduces noise breaking out from the duct into the surrounding space, and noise travelling along the duct from the air handling unit. It is commonly specified as internal lining in the airstream, sometimes combined with external acoustic wrap depending on the noise target.
How do supply and extract differ?
Supply ducts carrying conditioned air usually need thermal insulation to protect the air temperature. Extract ducts often need acoustic insulation to control fan and breakout noise. Chilled supply ducts need a vapour-sealed thermal layer to stop condensation on the duct surface.
Condensation control on chilled-air ducts
When a duct carries cool air through a warmer space, moisture can form on the bare metal. Thermal insulation with a continuous vapour barrier keeps the outer surface above dew point. Gaps at joints or supports are enough to let condensation start, so detailing matters as much as the insulation thickness.
Internal lining vs external wrap
External wrap is the default — mineral wool or foil-faced wrap applied over the outside. Internal lining is specified where acoustic attenuation in the airstream is required, and it must be faced to resist erosion and shedding. Some systems use both, with internal lining for acoustics and external wrap for thermal.
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