My living room, 3.3m x 4.4m, is easily heated up by a double panel, double fin radiator.
My bedroom on the otherhand (2.7m x 3.9m) struggles to be heated by double panel, single fin radiator. It was originally a single panel radiator which was replaced to address the lack of heat.
Both rooms are exposed on 2 sides, and the living room has also has a glass balcony door.
Originally a single panel radiator was on the bedroom internal wall, when installing the double panel radiator, it was installed under the window to improve convection.
For good measure I attached some radiator foils behind all the radiators although it hasn't resulted in a noticeable improvement.
The living room curtains rest on a shelf that protrudes ever so slightly over the radiator (less than an inch) and is directly above it. Same for the bedroom, but the shelf is about 20cm higher than the radiator.
I'm struggling to understand why the bedroom is struggling to be heated up. The radiator will be boiling hot to touch yet this isn't translating into a warmer room. The flat generally has poor insulation due to concrete walls but I have no issues heating up the living room.
EDIT - pictures: http://imgur.com/a/mJIoU
I did a few checks using a thermal leak detector (https://www.amazon.co.uk/Black-Decker-TLD100-Thermal-Detector/dp/B0044R87BE) and had the following findings.
Aiming the detector at the middle of the rad towards the top, I got a living room reading of 57.3C and a bedroom reading of 55.9C. I pointed it at the window away from an area above the rad and got a reading in the living room of 16.1C and bedroom 12.3C.
I think the difference can possibly be explained by the fact the living room had a balcony so the windows are not as exposed as much to the elements.
Using the same device and incense sticks, I've previously hunted around for draughts and did the 'classic' check using paper between the window and the frame to test the strength of the grip between the two (paper didn't slide out at all).
The thermostat is branded Salus and it turned up to max. Hot air is definitely emanating from the top