Hot water time - leave on constant?


Postby pen28 » Sat Jun 07, 2008 7:23 am

Can anyone help. I have a boiler (not combi) and I was told it was cheaper to leave my timer on constant instead of having it come on twice a day for the hot water. Not sure if this is right - can anyone help please.
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Postby htg engineer » Sat Jun 07, 2008 12:35 pm

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Postby plumbbob » Sun Jun 08, 2008 10:20 am

To even consider leaving the boiler on 24/7, you must have a cylinder thermostat fitted otherwise the boiler will be cycling regardless of the water temperature in the cylinder and will be very wasteful.
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Postby htg engineer » Sun Jun 08, 2008 5:43 pm

"To even consider leaving the boiler on 24/7, you must have a cylinder thermostat fitted otherwise the boiler will be cycling regardless of the water temperature in the cylinder and will be very wasteful."

How ?

the water in the boiler will only heat the water to the temperature set on the boiler thermostat. The boiler will only come back on when the water in the primaries have cooled. If the water in the cyclinder is hot, then the primaries wont cool very quick.

I know what you mean by having a cylinder stat fitted - but to say the boiler will continue cycling regardless of the cylinder temperature is rubbish - that means the water would end up boiling ????

When the temperatur in the primaries does drop - the boiler will come back on but only for seconds.

I know two people that have their hot water on 24/7 and one's a housewarmer back boiler, one's a potterton back boiler, both gravity HW - and the water is at a maintained temperature 24/7.

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Postby plumbbob » Sun Jun 08, 2008 8:38 pm

Now come on Htg, that is a silly post.

As you know in a "Y" plan system the tank stat providing there is no call for central heating, will prevent the boiler from firing at all and thus the water contained in the boiler itself and the pipework to the tank will be allowed to cool to ambient temperature.

As the cylinder unlike the pipework and boiler is heavily lagged, it will remain at temperature for several hours and consequently the boiler will not be called to fire at all. Compare that to the fact that the heat loss from the boiler and associated pipework will call for the boiler stat to fire every few minutes albeit for the minute or so you say. Don't you think that wastage is important then?

And to prove my point, why do you think cylinder stats are fitted?

And of course the boiler won't boil the water, just keep heating it up to temp again and again which is unnecessary.

I would also point out that on some older designed systems without a stat, the pump would be running for 24/7.

Your original post suggesting there have been no calculations done regarding the cost effectiveness between heating on a timed basis and a 24/7 basis is as far as I know, correct.

However what worries me about that theory is it's like saying a car will use more fuel if you only fill it up on empty rather than topping up at each garage as you pass. Not having a cylinder stat fitted is the equivalent of having the pump dribbling when you are not even on the forecourt.

But is the water required to be at temperature all the time? Well of course not! Not in the middle of the night and as you yourself pointed out Htg, not if you are out at work in the day.

Frankly, anything outside the cylinder that is heated unnecessarily is bad news and wasteful.

I have no idea how the idea that on a proper planned system, having water on 24/7 is more efficient than heating on demand, I just can't prove it either way but common sense asks why should it cost more to lift the temperature a good deal occasionally rather than lift a little way often when you have heat losses to consider.

Just think of paying for the heat loss from those 28mm pipes belonging to the people you know Htg, especially on a day like today!
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Postby htg engineer » Mon Jun 09, 2008 11:01 am

Yes I know why you have a cylinder stat - exactly the reason you're saying - energy efficiency, the stat will shut the system down when the temperature is met and will not bring it back on until the hot water temp drops.

Gravity system - pump running for hot water 24/7 ? since when ????

'And of course the boiler won't boil the water, just keep heating it up to temp again and again which is unnecessary.'

That's all i'm sayin the - hot water will stay at a constant temperature,
You said 'the boiler will be cycling regardless of the water temperature ????

'Just think of paying for the heat loss from those 28mm pipes belonging to the people you know Htg, especially on a day like today!'
yep - I have explained this to them, and as they're in their 70's they have the 'we know best' approach to life - so don't waste my breath anymore.

I'm not arguing that it is not wasteful - but to say the boiler will keep cycling regardless of the water temperature is incorrect, that sounds as if you're saying the water will continue to heat up - that's how it read to me.

I wouldn't have a boiler on 24/7 but people do - and i have no hard evidence to say that you save or waste money , some companies advise to leave heating and water on 24/7 as they say it costs more to heat from cold each time.

As for wastage, people work for their money if they or I want to waste it - that's their business. I don't agree with the government pushing that global warming is caused by humans - and will push anything that makes money - it's a process like everything else, what caused the ice age ? what killed the dinosaurs ? cars, boilers ???
live and let live

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