I actually bought a small electric heater for the table online for €30 and tested it over the weekend. The device is app-controlled and has 1500W. I managed to raise the room temperature from 17.5 degrees to 19.5 degrees in about 1 hour. I was really satisfied! Sure, it consumes a lot of electricity, but it's definitely worth it for a cozy darts evening with friends.
Advantage: Nothing large or fixed needs to be installed, it can also be used if the heating fails, it looks really cool, and it doesn’t take up any space at all.
The only drawback is definitely the power consumption. But I only turn it on when I spend a few hours in the darts room with friends (which doesn’t happen that often, especially not from November to March) – during the other months, you don’t need it anyway.
I will give it a try with that. If I then install the room divider with curtain, the heat certainly won’t be distributed throughout the whole room anymore.
Price-wise, it’s really attractive too :) I’m really satisfied with it so far and will keep it for now.