The basement should become warmer - underfloor heating, insulation?

The one radiator that is installed warms up the room as well. We tried it unintentionally when the thermostat broke off... Then the room was nice and warm but the floor was still unpleasantly cold. I don’t know what they did back then with the basement, but it seems to be basically uninsulated. That’s why putting up more radiators would only be a last resort, although probably the cheapest way. I still have 2 radiators here that we took out when we renovated the bathroom. But as I said, either I heat the room for several days before every party at maximum power or we have it warm upstairs and still cold feet :(

I can't quite understand the problem. We have similar conditions: basement bar (about 32m²), 1 radiator, house from the 80s, ceiling height 2.2m. Ok, your room is bigger, but I currently have 14°C in our basement bar without heating as well. With the radiator, I can get the room up to 22°C within a day, if you want that. Our problem is usually that when there are 15 people in the room, within 1-2 hours we are usually at about 24-25°C room temperature and the first ones want to open the windows. No one has ever complained about cold feet, as you usually wear shoes anyway. I have never seen underfloor heating in a basement bar and I also consider it not very practical, because it would also take extremely long to warm up the room and it would be difficult to adjust it afterwards.

For insulation alone, 2-3cm of insulation is basically useless. In my opinion, that won't do you any good and it's no more than a thicker impact sound insulation anyway. The simplest option from my perspective is to replace the tiles with laminate or vinyl. That at least feels noticeably warmer and then maybe add a radiator to heat the room faster.

I also believe that "Schuhe" would be the cheapest solution, but if the real wish is to warm the floor, then an electric underfloor heating system would be just predestined for this case. The installation height is low, the "lead time" and the costs are also low. And since the room is only used sporadically, electricity consumption plays a minor role.

Yep, that would be the best solution. If the room gets warm enough from the radiator. For the feet, E-floor heating. Done.

Vacuum insulation panels. Extremely effective (0.003 to 0.008 W·m−1·K−1), but unfortunately also very expensive.

Thank you for the suggestion. The things don't sound bad. However, I can hardly find any offers for them. Do they have another name? I also tried [Vakuumisolationspaneele] etc.