The key is balance. Radiators should be placed near typical cold spots in open plan living spaces – like by patio doors, large windows, or external walls. That said, you should also think about where people actually sit and spend time.
You could opt to position a radiator by the kitchen, with another near the lounge area, and maybe one by the dining table if you tend to eat at the table frequently. Avoid sticking all your radiators on one single wall or you’ll end up with half the room toasty and the other half clasping for warmth.
For further information, take a look at our article, The best radiators for open plan living spaces.