Why can't my radiator heat up my bedroom?

Question

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: https://i.sstatic.net/uAFh7.jpg

Further info:

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

Answer 1

That radiator certainly looks big enough to heat the room you describe.

The windows -- Maybe the living room window is better insulated than the bedroom window. You may be able to feel the difference by resting your hand on the glass. Also, the living room drapes may be better insulators than the bedroom curtains.

Drafts -- You can use a joss stick or a punk stick to detect drafts, and to monitor the convection in both rooms. You will have to sit still for a minute to let the eddy currents from your moving around to die down.

With concrete construction, any cold drafts would likely come in around the ceiling, or around the window. Also check switch and outlet plates.

Convection -- When a radiator is under a window, the downdraft from the window fights with the updraft from the radiator. Usually one or the other wins out, so there is circulation throughout the room. Maybe in your case they almost balance.

The real mystery is, of course, why the convection in the living room is so different from that in the bedroom. With patience and joss stick smoke you may be able to see what is really happening.

A remedy -- In my house I had a similar problem. I solved it by adding a room fan, on its lowest setting, to move air over the radiator. My bedroom went from uninhabitable to toasty. If you have any kind of fan or blower on hand, try experimenting with blowing against the wall below the radiator to assist the natural convection.

If this works I would suggest two small (5 inch or 8 inch dia) table rotary fans placed on the floor, about 4 inches from the baseboard, blowing toward the radiator. I would rewire the fans in series for lower speed, but that's just me.

Answer 2

Check the radiator has enough power to heat-up the room: use this tool, insert the room measures and choose your building type (if it's an american-style woody house choose pre-1980 low insulation even if it's newer), then look if the required wattage matches with the radiator you choose for the delta-t you use (60°C flow, 10°C delta).

If match, it means that your house is really leaky, if your radiator rating is lower, you have to put on a bigger one (or increase the flow temperature on your boiler)

Also check your thermostatic valve data-sheet as most valves couldn't be installed vertically, and this kind of installation may lead to misbehaving