[changoplatanero]

how do you ventilate without losing all the heat?

[CrazyStat]

Heat recovery ventilation [1] can bring in fresh air and output old air while recovering the vast majority of the heat.

[1] https://en.wikipedia.org/wiki/Heat_recovery_ventilation

[voisin]

These are only compatible with forced air systems, correct? I.e. using in-floor radiant heat would require an entirely separate ventilation system with heat recovery?

[CrazyStat]

Correct.

[thatguy0900]

https://www.energy.gov/energysaver/whole-house-ventilation

Energy recovery ventilation systems gives a good description

[jhgb]

Recuperator ventilation, presumably?