Header Tank sharing hot and cold supplies?

[george (dicegeorge)]

Is it ok to have just one header tank for both hot and cold water?

Is it a good idea to have the hot water take off lower than the cold, so that if the tank runs low (if someone has all the taps running) the immersion heater will not run dry?

Presently there is a huge victorian tank for cold water which feeds a smaller header tank for the hot water feed.

The original huge tank was a bit higher than the hot water header tank, how much difference will a height difference make? I guess it will mean that the taps run a bit slower.

The plastic tank I am installing is 181 litres / 40 gallons

[george]

[Heliotrope Smith]

It is normal practice to use one tank only for cold supply and the supply to the cylinder.

It is not possible to run the cylinder dry by running taps.

Are you sure that the smaller tank is suppling the cylinder and it is not the feed & expansion tank for the boiler?

[Dave Plowman (News)]

The storage tank can't run dry - the water take off is from the top, not bottom.

Strange. Perhaps it made the pipework easier when adding the hot circuit.

It's usually the hot which is slower due to longer pipework and therefore resistance. But the more height you can get the better.

[<me9]

As long as the originals were supplying water to taps, and not topping up the heating system.

True, and it is accepted practice to have the cold take off lower, to avoid any scalding risks from mixer taps.

[Onetap]

On the contrary it is good practice to have the cold slightly lower than the hot water cylinder's cold feed. The reason is that someone using a mixing tap/shower won't get scalded by the cold running out while the hot is still going. A thermostatic mixing valve should stop the cold in that event anyway, and we've all tested out TMVs recently, heven't we?

[Onetap]

Darn! Brain malfunction.

A thermostatic mixing valve should stop the HOT in that event...........

[John Rumm]

ok, and quite normal...

No, you want it the other way round - so if you drain the header tank completely, the hot stops before the cold. Saves a risk of scalding.

(no need to worry about the tank running dry - it can't since it is emptied from the top and filled from the bottom - once you have no pressure from the header the water just sits in it)

It probably made sense to someone when they installed it!

1 bar of pressure is 30' of head. So in absolute terms very little, although in relative terms you may find a shower head that is say only 4' below the header tank water level, gaining an extra couple of feet makes for a 50% improvement.

Don't forget the tight fitting lid...

[george (dicegeorge)]

John Rumm wrote: xxxx

Why tight?

Isnt it just to stop spiders getting into the water?

[g]

[John Rumm]

Well you want a water bylaw kit - as you say keeps crud out etc. So tight as in not a board just sat on top...

[Dave]

We get more crud in the cold water storage tank from the water itself. The bottom of the tank gets a coating of black crud. When our US visitors leave tomorrow, I can find time to get rid of it.

I have posted in the past about this and wondered if I could put something in the tank to break it up and flush it out through the cold water taps. I was advised to use a brush to break it up and flush out.

Dave

[<me9]

I've put a cupful of bleach in a couple of times and left it a few hours, then thoroughly flushed the system. Since then I haven't had to repeat the performance, the black crud hasn't returned.