I'm just using it as a space heater for my study, which is also where I work from. While using the computer in Winter I just switch on f@h for both CPU and GPU (AMD 5700x and 6700xt), and this heats up the room. It's a good 300-400W. I have home assistant telling me the temperature in the room and it bugs me to turn it off if it's too hot. That's my "temperature control". I didn't build anything, the computer is just under my desk and it heats up my room.

Originally my plan was to have F@H automatically turn on and off based on temperature, but it turns out the power is low enough and the lag is high enough that you switch it on in the morning, and then once the room is upto temperature you can just switch it off and the room will stay warm the rest of the day.