Radiators and convectors are placed at the HVAC zone level. To place a radiator or convector, navigate to the HVAC zone, click on the Add radiative-convective unit tool and then select the required unit from the drop-list. Then, making sure that the cursor is inside the boundary of the required zone, left click with the mouse to place the radiator/convector.
The unit will be automatically positioned at the bottom centre of the zone:
