Install the ventilation system outside?

Hello, I wanted to ask if a ventilation system always has to be installed inside the house, or if there is also the possibility to install it from the outside (directly on the house wall) and then insulate the entire house with Styrofoam. Or are there problems regarding thermal bridges? The house is completely detached.

If the pipes are in the insulation, there is naturally less insulation at this point and thus a thermal bridge. If you want to retrofit a house with a ventilation system, consider a decentralized system.

When installing components into the insulation, all the hairs on the back of my neck stand up from an energy perspective. Our structural engineer = energy consultant has strongly advised against it, as it will lead to thermal bridges.

When installing components into the insulation, all the hairs on the back of my neck stand up from an energy perspective. Our structural engineer = energy consultant strongly advised against it because it will create thermal bridges.

That's why I'm asking :)

Now one more question: If I have 20 degrees in the room and 0 outside, then the air in a decentralized ventilation system is exchanged... On average, 10 degrees should come out. Isn't that a huge energy loss? Sure, if I open the window, air at 0 degrees comes in, but I only ventilate once a day? Regards

Not necessarily. Decentralized systems also exist with heat recovery and an efficiency of up to 90%.