Location of radiators

your choice, in theory the position of the rad does't make any differance in a closed room, it will radiate heat from the sourse (radiator) and the radiated heat will convect upwards travel onlong the ceiling and fall to the floor where its attracted back to the radiator by the convected currents,
In reality if the woman wants furniture against every wall, its best under the window unless, she wants long curtains to the floor then ts best where SHE says,

 

I just removed a single (big) rad from the centre of our living room and replaced with 2 rads at either end of the same wall as the big rad was so central that we couldnt put our sofa anywhere whithout the heat hitting it from that rad! Check to see if you have any big items of furniture that will be in the way of where a rad might go.

 

As said above - modern rads are far more efficient, and also much better at circulating the heat upwards and around the room, so positioning for heat is not so critical.

But do think carefully about its cosmetic impact and furniture location. Our main rad is behind the sofa, but it's 2 to 3 feet in front, so doesn't affect how the rad heats the room (double-convector).

 

Going back a few years I worked for a firm which was involved with the EAGA installations, on these it was a requirement that the radiator was always installed on an internal wall. When I started back in the 70's we put the radiators under windows for two reasons, first they believed it would convect the heat better under the window and second your less likely to want to put any substantial sized furniture in front of it.
My current thinking, you put it where it suits you but do make sure each one is sized to suit the heat loss for each particular room. There are plenty of online calculators to help you get the right size Rad.

 

Is your boiler a 'combi' type? If so, definitely stick with the larger size, as this is what delivers your domestic hot water. And a seemingly over-sized combi will modulate down the suit the rad system, so no chance of 'overpowering' it.

 

The insulation may have improved, but the heat loss through 1m² of d.g window is still 4 to 6 times greater than through 1m² of cavity filled wall. So you will still get the same problems with draughts near the windows.

 

Under windows is best (with short curtains) as it dead space in a room.
Rad will heat about 90% by convection, less than 10% by radiation.
Tall, narrow column radiators add a modern look to a room and don't take much wall space. But will cost more though. Make sure you've got a solid wall to fix em to though.

 

they're not draughts Sam, they're convection air currents, draughts come through open doors or open windows or beer kegs

 

I thought that draughts was a game played on a chequer board

 

yes, that as well dave,

 

Maybe they are; but they will feel like a draught to the average occupant.