If this hasn't already been said: lag the tank, fit a timer. My heating heats the DHW for a couple of hours in the early morning, and that's it until the following day. Tank stays hot through the day more than sufficient for bedtime ablutions, because it's well lagged. If you need to draw off a lot of hot water later in the day you could always set the timer to give an early evening boost.
By insulationg it?
Even if you switch the system off at bath time you're still going to have a lot of heat in the cylinder overnight. If you care at all about run cost your cylinder should be insulated, in which case there's very little saved by turning the HW off - in winter, approximately nothing, since lost heat effectively does the same job as CH heat.
The one time it would make a bit of sense to turn HW off is if you're one of those people that bathe once a week and otherwise wash cold. But those folk are pretty well gone now.
Requiring the ability to run a CH system with CH on and HW off made sense once. IMHO it no longer does.
NT
With good lagging, relatively little heat will be "lost". However also keep in mind where it is lost to - i.e. it ends up leaking into the house in most cases, where it will simply reduce the amount that needs replenishment from the CH at this time of year ans so is mostly cost neutral.
I think it rather depends on what you mean by "HW off"... In many cases the traditional Y plan layout makes less sense that it used too when boilers had fixed rate outputs, and cylinders were slow recovery types that could perhaps only absorb 5kW at best. In those situations having both on truly "at once" was worthwhile.
In more modern systems W plan or S plan often makes more sense - with serial rather than parallel operation of DHW and CH.
I meant over a longer timescale, ie having the programmer set to HW off - it just isn't useful afaics.
NT
Spose it might for frost protection while on holiday etc.
Are you saying that W- or S-plan systems are serial, or just that they allow for that option? My S-plan system, only two years old, is running parallel ATM, with the boiler supplying heat to both CH and DHW simultaneously.
It makes sense if you have a modern boiler with flow temperature control and a suitable control system which makes use of it. Running water at 30C throuch a cylinder coil is more likely to cool the cylinder, not heat it!
Just changed my S plan to W plan for this reason.
In article <HYxIF.285955$ snipped-for-privacy@fx25.am, snipped-for-privacy@blueyonder.co.uk says... HW and both.
You missed a trick there, Adam!
Just been reading this thread out to Helen who pointed out that you forgot about finally using the bath water to flush the loo!
W is always serial - there is no mid position, so you can only have CH or DHW but never both at once. (its also what you typically get with most combi boilers)
S Plan(+) can be either, but is the only common plan that allows for more than two zones, so becomes the plan of choice in many cases even if the "parallel" operation option is never used.
(I use S+ with three zones, two CH, and one DHW. Since I also use weather compensation, the CH flow temperature would vary rarely be high enough to also heat the DHW - so the system will never operate the DHW in parallel with CH, although it can operate the two CH zones in any combination)
Troll. Moi?
I don't know why this is so difficult to grasp: The hot water cylinder contains a full amount of piping hot water after one hour on the boiler. I use the water for a bath and washing up. I have no other need for hot water -- apart from the washing machine every 10 days. although the washing machine has its own heater, of course.
Therefore there is no need whatsoever to have the boiler constantly firing to bring the cylinder temperature up again if I'm not going to use any more hot water that day.
Not only is the volume of hot water sufficient for a bath and the washing up, I'm talking about washing up several times a day, plus washing my hands after using the facilities. I don't have a dish washer.
MM
It is insulated, and very efficiently. That's how the one hour's worth of boiler use provides enough hot water until the next day.
MM
The cylinder IS insulated! On your second point, you're suggesting using the hot water cylinder as a form of central heating when I've got a perfectly well-functioning central system anyway?
"Let's switch off the central heating and sit around the hot water cylinder in the airing cupboard, folks!"
I have a bath three times a week and the one hour on the boiler provides all the hot water I need and then some.
Well, sorry, but that's the way I do it.
MM
You haven't provided any valid reason *for me* to have the hot water on all the time.
Do you have a kettle of water boiling all the time in case someone wants a cup of tea?
MM
It "leaks" upwards (where all heat leaks...) and upwards is the loft, as the airing cupboard is on the first floor.
MM
Of course I'm not. It looks like you're being facetious.
Sure, do whatever works for you. I only mentioned it since people often get overly concerned about the costs of DHW production, when in reality they are typically dwarfed by the space heating costs.
Absolutely. During the summer, when the CH is off, the HW burns a very small amount of oil to get me my tankful of very hot water. The heating oil lasts a very long time.
MM
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