Doesn't it also depend how you're using the heating? An oven you're almost always using from cold, so it makes no difference. But if you turn your heating on and off more frequently than the time it takes to return to ambient, than it's starting from a slightly higher temp if you last had it at 21 rather than 20. Whether it's a noticeable difference is another question.
Not sure what you mean.
There are two temperature settings for central heating; circulating water temperature and target room temperature.
If the room is below the target temperature, the thermostat 'calls for heat'. That starts the water circulation pump running. If the water temp in the boiler is below the circulating water temperature, the boiler will fire, and continue to fire until either:
- Circulating water temperature reaches target (measured on return to boiler)
- Room temperature reaches target
If it is the second, the circulation pump will also stop running.
If your radiators are undersized for your boiler, the boiler will cycle on an off frequently (which is bad for the boiler).
Setting the room thermostat to a higher temperature has no effect how long it takes to get to temperature.
Setting individual radiator thermostatic valves to the maximum WILL heat up the rooms faster. There is a case for having all radiators open to full in rooms that are frequently used. Put thermostat in a hallway or something, set the temp lowish (for your standards), and open rad valves right up in the living room, kitchen. The living room and kitchen will get toasty warm, the rest of the house tolerable.
