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[scotview]

But.... when designing a wet system if one wants different temps in different rooms, and one sizes the rads accordingly, it works, even without internal wall insulation. Provided of course that one keeps the doors shut.
V8

Yip, your right, here's an example. Our bedroom & ensuite shower room is a zone. When we waken, say 7 am, we set the temperature to 21 degrees. It takes our small 15kW gas boiler about 12 minutes to get the room up to temperature (it's only heating that room), there are two towel rails in the shower room so it gets lovely and warm quickly. After we get up we set the bedroom temperature back to 14 degrees and the temperature decays throughout the day. I generally set the bedroom temperature to 20 degrees at 10 pm, by my phone app, and the room is lovely and warm at bed time. All this could be on a timer on the local stat but we find it works better to set temperatures as required.

So, only heat the room when needed (generally for 12 minutes in the morning and evening). Save energy and have luxury of showering at 21 degrees in the shower room. What's not to like. BG said our boiler was under sized at 15 kW but it works perfectly well with zone heating and has good modulation.

I recon most gas central heating systems are grossly oversized and could be a lot more user friendly and cost effective.

[DrFfybes]

If the outside walls were perfectly insulated, then after a while the entire interior would reach a uniform temperature (and you turn off the heater or you bake). In practice the outside walls can be pretty well insulated, an order of magnitude better than an interior wall is reasonable. Making reasonable assumptions about the geometry that means the temperature difference between rooms is an order of magnitude less than the temperature difference between the rooms you want to heat and the outside. So outside at 0C, rooms you want to heat at 20C, shut off rooms 18C.

If the outside walls are only as well insulated as interior walls you have outside at 9C, rooms you are heating at 20C and shut off rooms at 10C.

Presumably you only have one radiator in the middle of your house then ?

AIUI stud walls between rooms (except en-suites) need to be insulated... ours certainly are (well, the ones that aren't solid brick anyway).

100mm rockwool in a stud wall has an R value of 2.27, plus the plasterboard (2 x 0.45) making about 3.2 in total. You'd be doing well to find a typical UK house with an exterior wall of 10x that. Internal brick or block walss will alos have quite good R-value.

There's also the factor of rising heat, a downstairs unheated room will usually be colder than an upstairs one, assuming there is loft insulation.

Paul

[9873210]

If you shut down a large proportion of the house then perhaps zoned heating and insulating interior walls makes sense, but that's not how most houses are used. Few people want to be restricted to less than half the house or have to grab a parka to visit the loo....

But.... when designing a wet system if one wants different temps in different rooms, and one sizes the rads accordingly, it works, even without internal wall insulation. Provided of course that one keeps the doors shut.
Or at least, it did in our 1920 house with its brick internal walls and single room stat in the hall.

It works in your 1920 house because there is little or no little insulation in the outside walls. If the outside is insulated more heat leaks between rooms than to the outside and the interior reaches a more uniform temperature.

Poor insulation is a bug not a feature.