thank you for your answer
but, after spending 30000 euros minimum on the heating system (geothermal/UFH) with a tight budget, 5000 euros extra is a lot of money!
that's why we definitely want to install something cheaper or the HRV, but by ourselves. but the engineering part seems very complicated...
for a quote for a simple ventilation system, we got none cause we didn't find anybody who would waste their time doing it: not interesting enough for them financially, I suppose!
any tip on how to install the HRV ourselves? how much would materials cost (2500sq ft)? and where can we buy them?