Yes Homekit Device Integration. I too have them on another network, but I am repeating mDNS between my main LAN and my IoT VLAN
I just want to confirm - you say you can control your heat pump (on and off) WITHOUT any internet connection? Your HA can connect to and control the Mysa device?
I’ve been trying to find some sort of Mysa API but it appears to be a closed system requiring the internet to make it work.
I do not have Homekit/Google/Alexa or any other internet spyware, just a stand alone HA and no internet connection for IOT.
I don’t think there is an open API. They are using the HomeKit support feature of the thermostat. Use the HomeKit Controller integration in home assistant and it will find native HomeKit supported devices on your network (that are not connected to another HomeKit controller/hub). Easy. No apple hardware needed.
Edit: no internet needed either for HomeKit. It runs local unlike Google/Alexa
You are correct, add the Mysa thermostat to HA as a HomeKit device, and it all works offline
Do note that you lose some functionality, like fan-only mode and swing