Hot water - timed or on constant - what's more efficient?

[voicey]

We've moved into a flat where there is a communal boiler which routes hot water to radiators and through a mains pressured hot water tank (indirect of course). Energy is metered and charged at the same price regardless of when it is used. In the past I've always had a timer on the hot water to heat the tank up in the night ready for the morning. However - would it be more economical to have the timer on constant (there is an option for this) - so that when hot water is used the heat is topped up - or just to have it timed for the night time?

Or should I find something more important to think about....

 

[kevnurse]

I would suggest that you trial both methods, trying to use the water at a similar rate in both cases. The longer the trial period for each method, the more accurate your comparison will be.

 

[D_Hailsham]

Is the hot water tank well insulated, e.g one or two inches of factory installed foam?

 

[TicklyT]

I was just wondering how the heating is metered, as the flow temperature, return temperature and flow rate are all significant.

If the return temperature isn't monitored, depleting the stored water before re-heating, or maintaining the cylinder temperature significantly below the heating water temperature may be more efficient for you than maintaining a high water temperature.

If both are monitored, that's a different ball game.

Trouble is, reducing the stored hot water temperature too far may invite nasties like legionella to move in.

 

[bengasman]

...Trouble is, reducing the stored hot water temperature too far may invite nasties like legionella to move in.

It's unvented.

New(ish) unvented cylinders are well insulated, so there will be little in it to stick it on a timer in your case.

 

[Mottie]

I’ve resurrected this thread rather than start a new one as I had a 'discussion' with someone last week for exactly the same question. I have always kept our hot water on constant. They have there’s on just once a day. I say constant is more efficient and liken it to keeping a car at a steady speed. Their method is akin to the car slowing down and then accelerating back up to speed which will use more fuel. We both have the same circumstances - two people living at home, both have one shower each, every evening. Dishwasher and washing machines are both cold fill. Don’t know about their hot water cylinder but ours is a two year old unvented one and very well insulated - I get no heat off of ours and the only heat in the airing cupboard comes from the pipes that are routed through there.

So, who's right or is there so little in it that it make no difference.