[perceptronas]

Windows>

Heat exchangers can be up to 90% effective at saving heat, while window ventilation will be 0%.

Noise pollution>

In my cold climate, whoever goes with heat pumps - they usually go with "air-water" systems. Meaning only outside you have fans and inside you have your typical floor heating.

[dx034]

Much higher than 90%. The one I had in the passive house I lived in was specified to 98% at most temperature ranges. I guess most of the time the temperature difference isn't that large anyway (<20C) so they will lose next to no heat.