Where in a room is the best place to have radiators (outside wall etc)?

[Pannacotta]

We need to renovate our ancient heating system and many of the huge rads are below windows and we want to have full length curtains.
Is there any reason why they are mostly on outside walls, are they not just heating the cold air coming in? Would they be just as/more effective on inside walls?
Thanks

Best place, imho, is inside wall, just by a door. You almost never want to put furniture just in front of the door, whereas people often want a bed or table etc. under the window.
Rads on outside walls radiate a lot of heat to outside, on an inside wall they keep more heat in the house.
I don't understand why under windows was traditional, either.

But if you put it just by the door into each room, every time someone enters the room they help to move air near the rad, and consequently into/around the house much more efficiently.

Thanks lljkk, that makes much more sense to me, and woudl make it much easier for us in terms of both curtains and furniture.

is underfloor heating out of your price range?

Radiators are put on the outside wall, under a window because otherwise you get a steep temperature gradient across the room.

tis true about the temp gradient thing. We have a room with one by-door radiator (inside wall), and one under-window. Under window one isn't working just now, and the room is MUCH colder on that side than the other.
However on the flip side, if we do just want to have one radiator on, then the room is bearable if the door one is on, and cold if it's just the window one, suggesting that the door one is heating the room more efficiently.
And in my experience, having radiators behind curtains is super-ineffective. We have this in bedrooms, and our compromise is to have thinnish curtains and thicker blinds mounted inside the window frame. When the heating comes on we shut the blinds but not the curtains; curtains get shut when we come up to bed.

Its hard to know what is best as I really want long curtains in all the bedrooms/reception rooms. It is a cold house with tall ceilings. Have been trying not to use the rad in our bedroom and the temp hovers around 16 degrees.
We will update the system but cannot afford underfloor heating, sadly.

This may help.

Thanks lala, that is v helpful.

DH and I have been having this discussion (row!) for years. he says the rad under the window heats cold air as it comes through into the room. i argue that that rad under the window is spending its time trying to heat up a freezing cold pane of glass thereby not heating up the room.

have you costed out your curtains? (I was personally shocked at how much it was to curtain my bay window in my Victorian house and couldn't stretch to having them meet the floor which would have been 2.7 metres .. at 2.3 metres they cost me £450 over 6 years ago .. and that's just ONE window treatment)

Curtains will be v pricey Twiglett but we plan to get them done room by room. Thick lined curatins help loads with retaining heat IME so think its worth it...

My PILs have thick curtains with rads under the windows. To heat the rooms they need to tuck the curtains up on top of the radiators - which looks horrible and still isn't that efficient!

I hate radiators under windows as I always want long, sweeping curtains...BUT, technically it is the most efficient place to put them.

I've tried arguing with DP (who is a carpenter and builder but from a boffin /scientist background) and unfortunately he is right. Although I don't care - I still hate them under windows!

We've compromised and gone for shutters