Best place to site a radiator in a room is under the floor.

I would have thought that usually the window would be the coldest spot anyway?

As Paul says, the traditional positioning is to avoid drafts - the cold air off the window (sinking) is balanced by the warm air from the radiator (rising). The absolute worst is to have the radiator on the opposite wall to the window, as that can create quite a strong circulation (down the window, across the floor around your ankles, up the radiator and across the ceiling).

If you can't do under the floor, another alternative could be skirting board heating (for an example, look here http://www.discreteheat.co.uk/) , which should give an even and unobtrusive heat throughout the room.

Obviously the guys from Discreteheat haven't been around very long. I was fitting Finrad skirting heating 30 years ago. The biggest problems I found were:
Making sure you had enough heat output. It was not always possible to get enough skirting length.
You have to like the style. It ruins the appearance of some older houses.
Lots of fiddles to fit. You take the old skirting off and there is a lot of making good. The floorboards often do not reach the wall and you have to start fitting fillets to stop the air leaks.
Detail problems when you get to doorways and pillars.
Personally I would rather take the floor up and fit UFH.

Underfloor heatings great, fitted it quite a few times in screeds, I've yet to fit it upstairs, cost reasons mainly
most my work is renovations and extensions
It makes sense to me to try and hang the rads on an internal walls as Mike suggests
but this creates cold spots in the room, especially if there is 2 external walls

still not sure of the best place? other than not opposite a window
skirting rads look got but there not cheap and as said to everybodies taste

workaholic, how does underfloor heating work with your ideas on thermally responsive buildings , with its lower flow/return temperature
it needs some time to get going, back to the thermal mass debate, do you suggest a higher F/R temp.?

Yep, Best as in least energy used

thanks Tony

Jim

I have moved most of my radiators to internal walls and crucially fitted a new very efficient condensing boiler. Gas bills have literally halved from what they were. No problems with cold spots that I can percieve though I guess all houses are different

Yes, I agree, but think that that is a misconception. I've done quite a lot of thermal modelling which indicates that ugrading a gas boiler is the single best thing you can do in an old uninsulated building [walls that is]. My old boiler would have probably lasted another couple of years but was starting to need fair bit of maintenance. I assume the efficiency was also where near what it should be. It also had a pilot light [as most old boilers do] and this is often not considered when looking at cost of replacement v payback.

Workaholic
This sounds simple and economic , I think I'm starting to sway in your direction
Do you have many examples of your approach , and rough ideas on energy usage once lived in

cheers Jim

Heat can only be absorbed by internal walls once so you cant wast any there.

It may well be the most efficient place to put a radiator in terms of heating the house and feeling comfortable

It is also the place to put it to maximise heat losses and so it cannot be the most economic place to put it.

I hope we can get to a consensus on this. I'm on the verge of moving a radiator to an interior wall from under the window. Now I don't know what the hell to do.

I sympathise Tony. The internet is fantastic but the problem is that everyone who has an opinion and cares about the environment offers their view. I just wanted to join the debate because projects such as the Yellow House in Oxford seem so serious but sadly perpetuate misunderstandings. People seem convinced but do they know what their homes would be like if they followed Scandinavian guidelines?
I've been following this debate in the UK (there is no debate in the colder countries of Europe!) since 1986 when I renovated a Victorian terraced house in Cambridge and consulted qualified heating engineers. In a couple of rooms I defied their advice along the thinking you refer to and was bitterly disappointed. Not only did cold air invade the rooms through 1970s replacement windows which condensed up (I dried them regularly to prevent mould and mildew forming), furniture inevitably ended up blocking the large radiators on internal walls making me turn up the heating even higher. I even had to hang on to a gasfire I had counted on pulling out and was only effortlessly snug in the rooms with rads under windows (which had much less condensation).
In Sweden I've lived in houses and flats from 1800, 1905, 1945, 1978 and 1990s with different building materials and very different insulation values - always, ALWAYS rads are under windows!
You can put it this way. If you have 2 rads in 2 identical rooms at the same temp for the same time, that alone will not determine the temperature of the room. Wall and window insulation and where you put them will. You can either put them where they stop cold penetration (and condensation!) or where they encourage it!
Hope you find this helpful Tony!

<In the same way as fanheaters inside doorways keep department stores efficiently heated.>

If you call that efficiency then I have no hope for you! Shut the door or have an air-locked porch.

The wall that the rad is sited on heats up much hotter than the rest of the walls in the room hence shows redder or white even on an infra red camera.

It follows that if the wall is hotter then the heat losses are greater and therefore the building must be less efficient in energy terms than it could be.

Commonly radiators are placed under windows too coincidentally just where the hot spots often are -- I rest my case!

No insulation will not stop heat loss it will only reduce it. If you put a radiator on a wall the wall will heat up warmer than the rest of the walls in the room and if it is on an outside wall then it will heat up the outside warmer too -- redder to the IR camera. And greater heat loss even with perfect insulation.