Why do housebuilders fit radiators to external walls, and /or underneath windows, where the heat can escape? Do they have shares in British Gash?
Radiators are traditionally fitted under windows because:
1. the convected warm air rising up from the radiator countered the downdraught from the air being chilled by the cold [single glazed] windows and poorly fitting casements so people can sit closer to the window without getting draughts, [not so much of a problem now with double glazing and better draught proofing]
2. radiators heat by convection currents and radiant heat directly into the room - both counteract the heat loss from the room + balance the colder zone next to the the outside wall, and,
3. radiators under windows don't waste useful wall space where furniture and beds can be located.
Better insulation and lower air leakage means that new build houses keep their heat better so it's not sso important. Gas boilers will no longer be fitted from 2025 under new emerging Building Regs so get rid of your free Government issue Gas shares before then.
[Edit: Beebo beat me to it!]