Check out Komfovent units if you want a ready solution. My setup is Komfovent HRV (over MODBUS TCP), NIBE heatpump (over MODBUS UDP + esphome-nibe), Vaillant gas boiler (over eBUS-WiFi) + a bunch of AirGradients scattered around the house. Nothing has access to the internet, everything is glued together with HA. Works surprisingly well :)