The fan was originally used in a heating system. The entire hot air based heating system from the 1960s was exchanged in favor of something more modern, but I did not throw away the biggish radial fan. The fan in from 1991, it was made by Ziehl-Abegg and has a 250mm diameter.

Here are details of its modern siblings

Fortunately, the fan can work without all the control electronics from the old heating system by simply connecting it to mains voltage.