Special attention has to be paid when it comes to insulating ventilation ducts. Distinguishing between 4 zones we recommend following insulation:
A) Ducts carrying air with outside temperature (intake and exhaust) within the thermal envelope
Vapour resistant insulation of 25-100mm, e.g. Armaflex or pre-insulated ducts. Without vapour barrier, normal insulation material will attract condensation and loose its insulating qualities.
B) Ducts carrying air with ambient temperature within the thermal envelope
Usually no insulation required.
C) Ducts carrying heated supply air within the thermal envelope
25-50mm of insulation, e.g. ductwrap.
D) Ducts carrying air with ambient temperature pertruding out of the thermal envelope
100mm of insulation, e.g. ductwrap.
Ducts of category A should be kept as short as possible to prevent heat losses and reduce costs for insulation.
Ducts of category D should be avoided, e.g. in a cold loft by placing the loft insulation over the ducts.
Please also note to avoid placing ambient ducts within the insulation layer of outside walls or ceilings. Weakened insulation is a cold bridge and reduced the efficiency of the HRV system.