How do I do this - suggestions?

[Nygge72]

I'm in the process of adding insulation to a summer cottage. There is an old "out-ventilation" pipe, very old model. Square-shaped. So my question is, are there modern ones that can be coupled with the old one?

If not, I'm considering whether it would be possible to just place a round pipe inside this one, then seal around it in a suitable way?

 

[maah]

A round pipe with some foam sealant around it becomes the simplest, cheapest, and best solution.

 

[Nygge72]

A round pipe with some foam around it becomes the easiest, cheapest, and best solution.

That's what I thought too.