Cold water tank

[Peter Spikings]

Hi,

Something that's been bugging me for a while..... may be missing something obvious here but what's the point of a cold water tank in the loft?

I have an indirect hot water cylinder with immersion but why can't that and all the taps be fed from the mains? I want to use water aerators on my wash basin taps but of course they need mains pressure to work. Also it takes up loads of room in the loft and is a minor flood hazard ;)

The only thing I can think of is water storage in case of the mains failing but I've not experienced that yet in 10 years of owning a house.

Thanks,

Peter.

[Bob Minchin dangling via a don]

Unless specifically designed for it, your indirect cylinder will not withstand mains pressure so don't try that without checking!

Bob

[shazzbat]

But AFAIK there is no reason why all your cold taps and WCs shouldn't be fed from the rising main, they are in my house. Although if you do the WCs, don't forget you'll need to change the ball valves too.

Steve

[Keith W]

Many years ago before water privatisation there were, I believe, regulations which did indeed require all premises to store a quantity of water in case of mains failure. This obviously no longer applies but many houses remain from when it did.

[Andrew Gabriel]

As another poster said, most hot water cylinders are not rated for mains water pressure. You can get ones which are, but they come with a number of additional complications.

It's still an important consideration in places of work, because if you lose toilet and hand-washing facilities (e.g. due to loss of mains water supply with no local storage), you pretty much have to send all your staff home. When designing things like data centres with high availability, one of the things to factor in is enough stored water to support the skelton staff required to be working on-site for a day or two (long enough to get water mains repaired or storage tanks refilled by road tanker). With the widespread use of lights-out data centres, that's less of an issue than it used to be in that much of the operations can be done remotely, but critical facilities still have to maintain staff on-site to handle hardware issues within allowable service times.

[Andrew Gabriel]

Toilet ball-valves used to me much quieter when fed with low pressure. That's much less of an issue with the more modern ones though.

My personal preference is to have kitchen and any basins used for teeth cleaning directly mains fed, but if you have a tank, tank fed supplies used elsewhere (e.g. baths, toilets), so you have some backup available.

[Peter Spikings]

Thanks for all your replies, especially since I posted then promptly forgot doing so, I'm good at that ;)

Good point about the HWC not being able to take mains pressure (I'll take your word for it). Can you get pressure reducing valves that would enable me to feed that off the mains? I know you can get flow reducing ones but that's not the same thing is it? :) If the toilets become too noisy I'll cross that bridge when I come to it.

Thanks,

Peter

[Bob Minchin dangling via a don]

See

Suggest you set to about 0.5 bar = about 16 foot head which will be about the same as a header tank in a two storey house.

Bob

[Heliotrope Smith]

It is NOT possible to feed an open vented cylinder with mains water no matter what kind of valve you fit or how low the pressure.

Neither can a normal cylinder be converted to unvented mains pressure.

The open vent must be kept open at all times so any pressure would send the water straight out through the vent.

[Woody]

The point that no-one has made.

If you have a hot tank running at mains pressure, what happens when you heat the water? Correct, it expands, but if it cannot expand then (Boyle's Law?) the pressure within must increase until you get to the ultimate - tank failure with all of the consequences.

The main idea of the cold header tank is that it feeds both the hot and cold bath taps (and any gravity fed shower) so both supplies are at the same pressure when delivered. If you have one tap from a hot tank and the other from mains then it will be difficult to balance flow and/or temperature, and there is also the possibility of back-feed via a mixer tap or similar which is not allowed.

[Andy Champ]

Boyle's law is for expansion of gasses.

Andy

[Keith W]

Guess the result isn't a lot different though ;o)

[Andy Champ]

More likely to split the tank, but less likely to take the roof off the house when it goes.

Andy

[Peter Spikings]

Thanks for all your replies...... I've looked at the tank plumbing and now get why you can't feed it from the mains.

I still want mains at the taps though, I'll have a dig around and see how the pipes are run, hopefully they'll be separate outputs from the CWT going to the tank/shower (has pump) and the rest.

I'll also be careful about mixer taps and potential back flow to the HWT, we don't tend to use hot water anyway at any sink apart from the kitchen and that already has mains on the cold.

Thanks again,

Peter.