On Wed, 28 Jan 2004 16:17:29 UTC, Velvet wrote:

Sorry, maybe I wasn't that clear. I know running the overall temp lower
leads to less heat loss, but my question was whether keeping it at (for
example) a min of 17C overnight (which would mean the boiler coming on
and off) would be more cost-effective than letting it cool down
overnight from the 19C in the evening to perhaps 14C before stat turns
it up to 18C for the morning blast of heat.

Bearing in mind I'd likely get no heat overnight from downstairs, since
I don't think they run theirs overnight, I lose a lot of heat quite
quickly, and I'm not sure if it's better to maintain the temperature,
albiet a bit lower, overnight, or just let it drop then have the boiler
firing for a long period in the morning to bring it back up to temp?

I look at this in terms of simple input and output.

To get it to a given temperature in the morning, you either leave it on
all night or you don't.

Heat loss is greater if you leave it on (as the differential is
greater), so you lose more heat overnight if it's on than if it's off.
In both case you need to replace the heat lost. You have more heat loss
to replace if you leave it on.

QED. Turn if off!
--
Bob Eager
begin by not using Outlook Express...