More efficient to have the water AND central heating on together?

[TheSpottedZebra]

Just that, really. I have a condensing (conventional) boiler, and we are getting to the time of year where we have the heating on in the evening, but don't really use hot water apart from in the morning.

Currently, we put the water on in the morning, as if we only had it on in the evening there wouldn't be enough for our showers etc. It wpuld have to be super cold for us to have the heating on innthe morning, and we'd never do so at night, as we're open window /fresh air people...

But my DP is insisting that it is actually more efficient to always have water and heating on together. Is he right?

[DancingLedge]

I'd love to know the answer to that.
Another, sometimes tense, discussion in our house: if the waters cold, and you want to heat it for a bath, does it heat quicker if you turn the heating off?

[wowfudge]

We have the water set to come on half an hour before the heating as I read on MN that the heating takes more from the boiler. If you have them set to come on at the same time, the water might never get to full temperature, depending on how long they are on for. We have the water on in the mornings only. Logic would mean that trying to heat two things would cost more, wouldn't it?

[TheSpottedZebra]

Logic would mean that trying to heat two things would cost more, wouldn't it?

Yes! That's what I think, but he is determined to insist that it's more efficient to have them on together!

[PigletJohn]

if you need to run them both for an hour, it is slightly more efficient to run them together than separately.

It is not efficient to run the heating when not needed.

HW only uses in the region of 25p worth of gas a day so is not significant, assuming you have proper insulation of cylinder and pipes.

[PigletJohn]

DancingLedge

If your cylinder is white, it can absorb a lot of heat from the boiler, and if the boiler is not very powerful, it may warm quicker if timed to start half an hour earlier than the CH. Older yellow boilers, or copper/red ones are slower to warm and absorb less heat so have less effect.

Green and blue ones, somewhere between.

Modern boilers usually have ample power to do both.

A well insulated cylinder loses so little heat that you can warm it 24 hours before your bath, if you want.

[DancingLedge]

Thanks PigletJohn. Cylinder is blue, so an in betweeny one. Boiler is about 5 yes old, and noticeably more efficient than the previous one. So I'll conclude that there's no justification for switching the heating off to heat the water quicker.(just like I always said,DS).
The water does indeed stay hot for a long time once heated. But sometimes runs out when a horde of visiting teens descends.