I have considered heating just the rooms required, the TRV
can be set to a schedule, and you can set a sequence so rooms are heated just before your going to use them.
However the main problem for me seems to be speed. Theory is sound, for £15 per room (2019 price when I bought them) you can set each room only to be heated when required.
But set wife's bedroom to 18ºC 24/7 she does not like room too hot, but allowing it to cool to 15ºC during part of the day, it was simply not re-heating on time for her to use it.
The same applies to the wall thermostat, theory great, set to 15ºC at night, and 18ºC in the morning, but in practice just takes too long to re-heat.
Last house had a Myson fan assisted radiator, I never realised how good it was, until I moved here and had not got it. It was so much faster at heating a room.
I have looked at the radiator selection charts, it says room of A x B size needs a C kW output radiator to maintain the room temperature, but that means CH running 24/7, what I want to know is no the size to maintain the room temperature but size to lift it from Eco setting at say 16ºC to comfort at say 20ºC in ½ hour.
In theory that should be easier than the size to maintain, as losses through the walls and windows will not effect it so much, but set up 4 thermometers in a room with heating on, and one can record widely different temperatures, sitting here at my PC, one shows 20.7ºC the other 18.4ºC and they are less than a meter between them.
This looks so easy
showing how the heat naturally flows, but stick a fan on the radiator and it works so much better. I looked at these
and thought what a good idea, so got a small fan and a thermostat which I put on radiator return pipe, so once radiator warm the fan would turn on. It turned on for about 5 minutes the radiator stone cold.
Looked at Myson, and realised the propriety type have nothing to restrict water flow, but this also means when off, hot water returned to boiler, this was OK before the condensation boiler, but with a modern boiler that return hot water will turn boiler down, OK if all rooms heating together, but selecting one room at a time, means other rooms return hot water and turn down boiler.
The fan assisted does not turn water flow on/off, but turns fan on/off or with better versions 5 speeds. This would work if radiators plumbed in series, but they are not, they are plumbed in parallel.