Condensation build-up on the outside of ducts containing material with a lower temperature than the ambient air temperature can cause problems. With a high humidity, air can easily condense on the outer surface of ducts. Once this has happened, the water can start dripping and cause damage an discoloration to ceilings and floors. Over time it can cause damage to the ducts that reduces their service life.

With the correct insulation solution, this kind of condensation is easy to prevent. Insulation, of the correct thickness, must be applied in order to keep the insulation surface temperature higher than the ambient air temperature, and an effective water vapour barrier must also be used in order to prevent moisture permeating the insulation.

Aluminium foil faced insulation is the best solution to prevent condensation because it has a very good vapour barrier. All joints should be taped very carefully.