I have an apartment with KNX thermostats and relay module with controls underfloor heating valves. I am thinking about integrating this into home assistant. AFAIK I need to get KNX to IP gateway for that. But do I need to call somebody to add that IP gateway to the KNX network or can I do it myself? I see that ETS is a software for programming devices, but I don’t have any existing configuration/project files, so I assume I will need to reprogram everything from scratch in this case?
You’ll need some way to communicate with the bus. Look at what is already installed - maybe there already is an IP interface, maybe you have a USB interface (which can be used by some software to simulate an IP interface - look up “knxd”).
If there is none you’ll need to buy one (you’ll probably find used ones for ~100€). Some can draw the needed power from the bus, some need an external power supply and some can use PoE. There are “KNX IP Router” and “KNX IP (Tunnelling-)Interface” devices - you’ll not need a router (they are way more expensive and trickier to install).
If you mean hardware-wise then I’d say, if you have to ask, you’ll probably be better off calling someone to install it.
On the software side its easy if you have the project file and an ETS license. Without its tricky, but doable - you will just have to assign an address to the interface that’s not already in use by another device (these are in the form of “1.0.20” and often written directly on the devices by the installer). With ETS demo-version you should be able to assign it, and maybe also scan your installation for addresses in use.
You can read and send to all group addresses currently in use. That means it is possible to do everything that can currently be done by buttons, displays etc. but you can’t add/change functionality to a device without ETS.
It will also be lots of work to find out which group address is assigned to which function.
I’d recommend to try to get the project file so you can at least have a look at how things are set up in your system. ETS is quite expensive, but you may find someone with a license who is willing to help you out with eg. exporting group address reports or something like that (without a license you can’t open the project file).