How to design and
install ventilation ducts?

In order for the ventilation system to be as efficient as possible, it is crucial that the ventilation ducts are dimensioned correctly and that the installation is carried out correctly.

This is partly about finding the right balance between wanting the ductwork to take up as little space as possible, while on the other hand taking care not to undersize it, as this will overload the ventilation system unnecessarily and may cause problems with the air change balance.

Get our full 32-page guide for selection and installation of residential ventilation right here: Selection Guide for residential ventilation

Choose the correct duct dimensions
Dantherm's recommended dimensions for the ventilation ducts are as follows:

  • Up to 80 m3/h: Ø100 mm
  • Up to 125 m3/h: Ø125 mm
  • Up to 200 m3/h: Ø160 mm
  • Up to 320 m3/h: Ø200 mm
  • Up to 500 m3/h: Ø250 mm


Prevent condensation and energy loss
It's also important to determine the insulation requirements for the ventilation ducts. If the ducts are placed outside the home's indoor climate zone, energy insulators will be required (typically 100 mm).

If the insulation does not cover the pipes in the ventilation ducts completely, condensation can form, which slides down the pipes and causes problems in the system. Just a small section of unprotected pipe can cause the entire system to stop running.

The ducts for fresh air intake and exhaust must always be condensation-insulated with a minimum of 50 mm insulation. Otherwise, condensation may form both outside and inside the pipes with moisture damage as a result.

Choosing the correct valves
A part of the dimensioning process is to choose the correct valve sizes in relation to the specific requirements for air change in the home.

Recommended dimensions of control valves:


  • Utility room, 36 m3/h: Ø100 mm
  • Toilet, 36 m3/h: Ø100 mm
  • Bathroom, 54 m3/h: Ø125 mm
  • Kitchen, 54 m3/h: Ø125 mm

Supply air

  • Up to 40 m3/h: Ø100 mm
  • Up to 60 m3/h: Ø125 mm
  • Up to 90 m3/h: Ø160 mm

For more information, please download Dantherm’s full Selection Guide for residential ventilation.