[GuB-42]

Yes, ventilation causes heat losses, but it is necessary.

There are ways around it though. The simplest is to not make sure ventilation goes where it needs to go. Modern buildings use mechanical ventilation to make sure every living space gets properly ventilated so one room doesn't get too much and another too little. Even better, some building use heat exchangers to heat/cool the incoming air with outgoing air, minimizing losses. Other techniques involve passing the fresh air underground, which, in a temperate climate gets you some free heating in the winter and free cooling in the summer.

Obviously, to limit heat losses, you want to reduce conduction and radiation too, which can be done without sacrificing ventilation.

[Cthulhu_]

The issue with heat exchangers and the like is noise on the one hand (can be suppressed of course), having it on the right setting (not too high if there's few people, not too low if there's many), and keeping the conduits clean (dust, moisture and heat is a great combo for some).