This may be a "how long is a piece of string" question, but how long should a room about 12' by 13' with solid walls and a bay window take to heat up from 16c to 21c? I know it's been cold recently, but it's taking 4 or 5 hours or so which seems excessive. The radiator, which is a double 160cm x 44cm (5'3" x 1'5") located in the bay, gets very hot and the boiler is a Worcester 28CDi. We have 10 radiators (includes 2 large doubles and 4 smaller doubles) in all. Since all of the radiators get very hot I wouldn't have thought the boiler is undersized. Is the radiator undersized for the room or is this just normal? It's only since I've installed a programmable thermostat (we didn't have a room thermostat before) that we've got proper control over the system and can see what's going on.