In the last cold snap I tired an experiment, in that I put a 6" desk fan running at its lowest speed under the 800 x 600 double radiator in the lounge, in an open-plan sixties design house.
The result was astonishing. In ten minutes, the thermometer at the other end of the lounge showed an increase of 1 degC (21.5 to
22.5degC), the temperature felt far more even across the lounge, and the TRV ran the system exactly: a setting of '4' gives the calibrated 21 degC, '5' gives 24 degC, and the interpolation is also correct: '4.5' gives 22.5 degC.The TRV is out of the direct air stream, and the lounge is noticeably more comfortable (but not necessarily warmer).