Christian McArdle wrote:

That's the crux of the question for me. The longer the heating is off,
the further it cools, and the more energy you need to put in to raise
the temperature again.


The efficiency will be higher letting it cool. The only effect that will
reduce efficiency compared to the alternative as that things get overheated
in an attempt to reheat the house to a comfortable level too quickly. This
is only likely to happen if the house is high thermal mass (i.e. thick stone
walls) and the cycling frequent. It would actually require a pretty
pathological set of parameters to make it less efficient, too.



Yes. Experience shows that it is marginally less efficient to do 24 hrs,
but not nearly as much as 'simple theory' predicts.

And teh iusses are as you say, thermal mass to insulation level ratios.

There is a lower limit on thermal mass - and that is the enclosed air
volume of the house.

As insulation levels rise to the point where heat input is drastically
reduced, the rate of cooling of that air mass makes it almost silly to
stop heating it. Air change factors start to dominate the loss equations
anyway.

There are side issues to do with whether boilers are more or less
efficient dong long burns to heat up big storage elemnents, or lots of
short blasts to keep a fast responding house 'up to temperature'

So it is complex.

Whilst timed CH in older less well insulated houses of lightweight
constrctions is definitely a huge saveing, its by no means clear ij teh
fcvase of modern well insulkated stuff.

My sister, in Sweden, has no concept of time clocks. The CH is switched
on in the autumn, and off in the late spring, and thermostats control
the house temperature. Thats all triple glazed 8"" rockwool no cold
bridges stuff.


Higher insulation would tend to reduce the heat losses, keeping the fabric
warmer for longer. This will reduce the differences between the two methods.


Exactly.



Christian.