Why smart thermostats don't always save you money

[richbee]

I like having my Tado room & radiator thermostats - so we can heat whichever room or rooms we are using. I'm working form home so my office is the only room which is being heated.
It detects when we go out and reduces the temperature to whatever I've got it set to.

There is a daily program for heating the bedroom up as we get up and go to bed, and kitchen at dinner time, etc, but it's quite often tweaked if we're doing something different - it's pretty obvious that you have to modify to suit, unless you have a very fixed schedule, and they are so much easier to control than the old fashioned central heating programmers - we can even ask 'she who must not be named' (Alexa!) to change the temperature if we want to

In most homes this isn't a good idea. The heat just migrates to the unheated rooms and all you have effectively done is reduce your heating systems emitter surface area and is less efficient.

I can understand that some of the heat leaks out into other rooms, but surely it's more efficient to heat 1 room instead of 8?

[AE-NMidlands]

I like having my Tado room & radiator thermostats - so we can heat whichever room or rooms we are using. I'm working form home so my office is the only room which is being heated.
It detects when we go out and reduces the temperature to whatever I've got it set to.

There is a daily program for heating the bedroom up as we get up and go to bed, and kitchen at dinner time, etc, but it's quite often tweaked if we're doing something different - it's pretty obvious that you have to modify to suit, unless you have a very fixed schedule, and they are so much easier to control than the old fashioned central heating programmers - we can even ask 'she who must not be named' (Alexa!) to change the temperature if we want to

In most homes this isn't a good idea. The heat just migrates to the unheated rooms and all you have effectively done is reduce your heating systems emitter surface area and is less efficient.

I can understand that some of the heat leaks out into other rooms, but surely it's more efficient to heat 1 room instead of 8?

Isn't this why building regs have required zoning of house heating for several years now? In our house it woukd be something like (much smaller boiler) heats 1/3 of house initially, say bedrooms early for when you get up, then downstairs living/working area through the day, then perhaps the lounge and another room in the evening and back to the bedrooms for late evening.
I thought one of the good things about blutooth radiator valves (on top of them being thermostatic valves) was that you can have virtual zones, so they are much more flexible...
A

[Swwils]

I like having my Tado room & radiator thermostats - so we can heat whichever room or rooms we are using. I'm working form home so my office is the only room which is being heated.
It detects when we go out and reduces the temperature to whatever I've got it set to.

There is a daily program for heating the bedroom up as we get up and go to bed, and kitchen at dinner time, etc, but it's quite often tweaked if we're doing something different - it's pretty obvious that you have to modify to suit, unless you have a very fixed schedule, and they are so much easier to control than the old fashioned central heating programmers - we can even ask 'she who must not be named' (Alexa!) to change the temperature if we want to

In most homes this isn't a good idea. The heat just migrates to the unheated rooms and all you have effectively done is reduce your heating systems emitter surface area and is less efficient.

I can understand that some of the heat leaks out into other rooms, but surely it's more efficient to heat 1 room instead of 8?

This would be the case if you lived in a tent or similar building where the temperature drops significantly when the heating is off. Otherwise (with a condensing boiler) it is almost always more efficient to keep the heating ON but at a sensible setback temperature when required. You are heating those rooms whether you like it or not.

In a "perfect" heating system TRVs would not be needed at all. In a "almost perfect" system the TRVs just act as temperature limiters for the W's introduced into the room by people in there at the moment, or calculation errors like bit higher solar gain.

In the UK, these bluetooth / smart TRVs can cause real issues; as if a single rad requests heat from the system - its unlikely the boiler will be able to modulate low enough for this demand and it will just cycle - absolutely destroying any efficiency. (And some boilers might report this behaviour as "super efficient" since they just determine efficiency as "% of time run at lowest modulation".)

Of course this assumes you have a nicely setup and designed system. A 30Kwh combi that has a minimum modulation of 7kw is going to cycle almost all the year in any house in the UK.