Water tank in attic or outside house?

[mike2016]

Hi,

A friend rang me up and suggested, why don't you put your mains water tank elsewhere than in the attic? It's standard on the continent he said, only UK/IRL do the attic tank.

 

New houses here in Ireland don't even install an attic tank and rely on mains pressure only but I'd prefer a buffer as they regularly drop pressure and it gives a reserve if water is cutoff for any reason.

 

But back to the suggestion, I've heard a plumber tell a story about a house where a pipe came off the attic tank and the occupants were out on holidays, water was coming out under the front door. The plumber was next door finishing a job. So naturally I'm keen to avoid this! 

 

I'm planning on building a timber frame so fire and water damage are high on my list to mitigate. I spotted this which might help:

https://www.greentherm.ie/product/rbm-stop-leak-brass/

I know there's no guarantee against a leak, I can install leak detectors but it still worries me....I plan to use Hep2O to minimize junctions...SunAmp for hot water, manifolds etc.

 

So, back to the main question - Attic Water Tank or place it somewhere else outside the main house (but insulated of course)? Thanks!

Edited June 16, 2018 by mike2016

[ProDave]

Just what do you want your attic water tank to do.  If it is to provide the header for your how water, that's not just last century, the one before I think. Have you never been in a modern house and marvelled at the hot water coming out of the tap with the same force as the cold water?

 

In warmer climates they put the hot water tanks outside, but that would not work very well here in the winter.

[Nickfromwales]

Ah, a guaranteed leak free system  ?

They don't make one I'm afraid as it's not down to the system it's mostly down to installer error.

Yes, components do fail, sometimes catastrophically, but more often than not leaks are caused by poor installation or incorrect fittings being used. 

When you go on holidays, turn the water off at the stopcock, simples . 

If your water pressure / flow rate is good, then IMO your about to unnecessarily increase your risks by adding components that you don't need. A 'tank' will give some redundant water storage, but an open tank won't be ideal for potable ( drinking quality ) water provision as I certainly wouldn't want to be drinking from a break tank when I've got cold mains available. Even more so if it's outside and the squirrels ( or worse ) start using it to give the kids swimming lessons . 

FYI, a "mains water tank" to me is a sealed accumulator, not and "open" aka "break tank". If you NEED an accumulator then it would be best off outside so it stays cold, rather than attain house ( ambient ) temp, and fitted in an outhouse or other frost protected location. The added benefit here is that if it ever fails the house stays dry, but, you can fit them in attics onto a drip tray to manage any drips etc. A stone resin shower tray would suffice for eg with the trap made off to an overflow pipe to outside. If there's a problem, simply engineer a solution.

My old boss used to say "If you're coming to me with a problem you should have waited a bit longer and be telling me the solution instead". In fairness we were usually in the middle of one ocean or another, so running to the merchants wasn't an option  

 

Best to first decide exactly WHY you want a tank before deciding what type and where it'll go. 

[billt]

9 hours ago, ProDave said:

Have you never been in a modern house and marvelled at the hot water coming out of the tap with the same force as the cold water?

 

We've just been staying in a relatives house with a modern water supply system (no storage tank) and marveled at just how absolutely awful it is!

Turn on a second tap and the flow in the first reduces, turn on a cold tap and the flow from the hot reduces. Takes ages for the hot water to flow (combi boiler), then, if someone turns on a cold tap the water gets hotter. Every house I've been in with a combi boiler has had similar issues.

 

When I redid our system (with 400l storage in the loft) I made sure that there was no interaction between the taps and the hot water doesn't change temperature when another tap is turned on. And the flow rate and pressure at each tap is adequate and equal for both hot and cold.

 

Our water supply is private, the mains electricity is not completely reliable, so it was eminently sensible to have loft storage which holds enough for at least 2 days and doesn't need power to pressurise the system. These days, if there was a decent mains water supply I would probably do it differently, but bad performance isn't a reason to condemn gravity stored systems.

[ProDave]

26 minutes ago, billt said:

 

We've just been staying in a relatives house with a modern water supply system (no storage tank) and marveled at just how absolutely awful it is!

Turn on a second tap and the flow in the first reduces, turn on a cold tap and the flow from the hot reduces. Takes ages for the hot water to flow (combi boiler), then, if someone turns on a cold tap the water gets hotter. Every house I've been in with a combi boiler has had similar issues.

 

When I redid our system (with 400l storage in the loft) I made sure that there was no interaction between the taps and the hot water doesn't change temperature when another tap is turned on. And the flow rate and pressure at each tap is adequate and equal for both hot and cold.

 

Our water supply is private, the mains electricity is not completely reliable, so it was eminently sensible to have loft storage which holds enough for at least 2 days and doesn't need power to pressurise the system. These days, if there was a decent mains water supply I would probably do it differently, but bad performance isn't a reason to condemn gravity stored systems.

A small combi is probably the root of the first problem. Fit a decent size or better, a system boiler and a good size unvented hot water cylinder.

 

The second problem may be poor mains water pressure or flow rate. you mention a private water supply.. Borehole? Spring? moire details.  If flow rate is poor fit an accumulator (big expansion tank rated for potable water) at the inlet to boost flow during high demand.

 

You "solution" of a big water tank in the lof just ensures that all the taps get low pressure and flow, rather than that only being a problem if you turn on too many at once.

[Jeremy Harris]

31 minutes ago, billt said:

 

We've just been staying in a relatives house with a modern water supply system (no storage tank) and marveled at just how absolutely awful it is!

Turn on a second tap and the flow in the first reduces, turn on a cold tap and the flow from the hot reduces. Takes ages for the hot water to flow (combi boiler), then, if someone turns on a cold tap the water gets hotter. Every house I've been in with a combi boiler has had similar issues.

 

When I redid our system (with 400l storage in the loft) I made sure that there was no interaction between the taps and the hot water doesn't change temperature when another tap is turned on. And the flow rate and pressure at each tap is adequate and equal for both hot and cold.

 

Our water supply is private, the mains electricity is not completely reliable, so it was eminently sensible to have loft storage which holds enough for at least 2 days and doesn't need power to pressurise the system. These days, if there was a decent mains water supply I would probably do it differently, but bad performance isn't a reason to condemn gravity stored systems.

 

We're also on a private supply, but rather than have a vented storage tank (lots of good reasons why these aren't a great idea) we have two 300 litre pressure vessels.  That way the water system is sealed, bugs can't get in, so there's no potential risk from a large volume of water being stored that could become a breeding ground for bugs in summer.  The pressure vessels also provide a near-constant pressure supply with the pump off, at a far greater pressure than from a loft tank.  The problem with one tap interfering with another can be eliminated by using two manifolds, one for hot, one for cold.  This not only removes the pressure drop problem, but it makes the plumbing a lot simpler and provides the ability to turn off the supply to a room from a central point.

[SteamyTea]

8 hours ago, Nickfromwales said:

Best to first decide exactly WHY you want a tank

 

1 hour ago, billt said:

and marveled at just how absolutely awful it is!

 

31 minutes ago, ProDave said:

A small combi is probably the root of the first problem. Fit a decent size or better, a system boiler and a good size unvented hot water cylinder.

 

And people wonder why I like vented.  They are cheap and easy to install, very reliable, and once heat loss is controlled, as cheap to run as anything else.

 

All this pressurised system is really a nonsense and just shows that is is hard to improve, for reliability and ease of use, on a vented system.

[MikeSharp01]

30 minutes ago, JSHarris said:

The problem with one tap interfering with another can be eliminated by using two manifolds, one for hot, one for cold.  This not only removes the pressure drop problem, but it makes the plumbing a lot simpler and provides the ability to turn off the supply to a room from a central point.

Yes, radial plumbing is the way to go if it can be arranged efficiently - IE put the manifold as close to the active middle of the system. (By active I mean demand led activity rather than run length as your kitchen taps will have many short duration demands while the showers will have occasional long demands and the bath very occasional very long demands and losses in these latter two from longer pipe runs are easier to tolerate, IE you can wait a little longer for the hot to come through, where as in the kitchen you want it NOW!.)

[newhome]

20 minutes ago, MikeSharp01 said:

your kitchen taps will have many short duration demands while the showers will have occasional long demands and the bath very occasional very long demands and losses in these latter two from longer pipe runs are easier to tolerate, I

 

Basin in the downstairs WC is another one that you want relatively quickly. It comes out slow in mine which means half the time I wash my hands in cold water as I can’t be bothered to wait. 

[Nickfromwales]

56 minutes ago, SteamyTea said:

And people wonder why I like vented.  They are cheap and easy to install, very reliable, and once heat loss is controlled, as cheap to run as anything else.

 

All this pressurised system is really a nonsense and just shows that is is hard to improve, for reliability and ease of use, on a vented system.

Best to explain which outlets get served by your gravity system before bragging it up too much 

The normal pressurised system delivers potable drinking quality water to outlets used for human consumption, so would you go up to the attic and fill a pint glass from it to have a nice thirst-quenching drink? Of course not. 

Your kitchen sink taps and likely your WC and electric shower ( if you have one ) will all be cold mains fed, if you haven't forked out a good few hundred quid buying and fitting a noisy shower booster pump, so best we lay all the facts down here as I wouldn't have a gravity / open pipe system fitted if it was free, sorry.

 

A combi is the worst example possible for delivery of hot water to outlets in a multiple occupant dwelling where others are flushing WC's / washing hands etc elsewhere at the same time ( for eg ) someone is trying to shower, so given that a combi is a very neat, cost-effective, practical and simple single-box solution, I don't think its fair to beat them up unnecessarily.

 

2 hours ago, billt said:

Our water supply is private, the mains electricity is not completely reliable, so it was eminently sensible to have loft storage which holds enough for at least 2 days and doesn't need power to pressurise the system. These days, if there was a decent mains water supply I would probably do it differently, but bad performance isn't a reason to condemn gravity stored systems.

If you have a pump that sends pressurised water to the 400L tank then I personally think you made a very bad decision there. A cold mains accumulator would have given whole-of-house, balanced, potable high flow rate hot and cold water and would wipe the floor with that gravity tank. No ta. 

 

Best we continue this chat by comparing apples with apples. 

 

 

[billt]

3 hours ago, ProDave said:

A small combi is probably the root of the first problem. Fit a decent size or better, a system boiler and a good size unvented hot water cylinder.

 

Not entirely. As well as the pipe run delay you have the delay of the boiler getting to temperature. (Yes, I know you can get combis with an internal store, but that is getting over complicated for me.

 

3 hours ago, ProDave said:

The second problem may be poor mains water pressure or flow rate. you mention a private water supply.. Borehole? Spring? moire details.  If flow rate is poor fit an accumulator (big expansion tank rated for potable water) at the inlet to boost flow during high demand.

 

You "solution" of a big water tank in the lof just ensures that all the taps get low pressure and flow, rather than that only being a problem if you turn on too many at once.

 

The supply is gravity fed from a spring into a 1000l tank in the garage; that is my "accumulator". Flow into the garage tank is both low pressure and low volume. The loft tank is intermittently filled from the garage tank by a pump operated by float switches. It runs every 2-3 days.

 

3 hours ago, ProDave said:

You "solution" of a big water tank in the lof just ensures that all the taps get low pressure and flow, rather than that only being a problem if you turn on too many at once.

 

I suppose that depends on what you want in terms of pressure; the flow at all outlets is entirely adequate. We don't want 10 bar pressure at our taps; the 1 bar in the kitchen is more than ample, and the .3 bar in the bathroom is enough to fill a bath quite fast enough. Obviously if you're into gigantic baths and high pressure - blast you from all angles - showers it wouldn't be adequate but if that was the case you would use a different solution.

[billt]

2 hours ago, Nickfromwales said:

If you have a pump that sends pressurised water to the 400L tank then I personally think you made a very bad decision there. A cold mains accumulator would have given whole-of-house, balanced, potable high flow rate hot and cold water and would wipe the floor with that gravity tank. No ta.

 

Maybe I wouldn't do it like that today, but maybe I would.

 

This was installed the best part of 30 years ago and was an update to a much older system; a pressurised system was a remote possibility, but they were very rare in domestic circumstances, very expensive, potentially unreliable and very difficult to research. Also, mains power was much more unreliable then and could go off for a day or more (it still does very occasionally) - we don't want to be without water for several days thank you.

 

But my point was simply that not all mains pressure systems are good and that not all gravity systems are bad; either can be done badly.

.

[Jeremy Harris]

You were also fortunate enough to be able to get a tank over 30ft above the ground floor outlets to give you 1 bar.   Our house has no loft, so there's nowhere to put a tank to gravity feed taps on the first floor, and the highest pressure we could get from having a tank in the services room to the ground floor taps is about 0.25 bar.  According to the MI's, that's too low to operate our dishwasher or washing machine, both of which need 0.5 bar minimum.  As well as the issue of not being able to supply drinking water from a vented loft tank, so needing some form of treatment for any potable water outlet, there's also the issue of needing large bore pipes to get a decent flow rate.

 

Our two 300 litre pressure vessels store potable water at 3 bar, which means we have plenty of pressure available to get a high flow rate using smaller bore pipes, which in turn means that we have less time to wait before hot taps run hot, as the pipe volume is smaller.  We also have potable water from every outlet in the house.

[ProDave]

@billt Your system is unusual, but not disimilar to many I see in remote places up here.

 

But I still by far maintain the best arrangement I have seen for such a system where the supply was from a stream at the bottom of the hill, pumped up with a hydraulic ram. So the water arrives in bursts, a small amount each time.

 

For this they have a SEALED underground tank which is where the water goes.

 

From the underground tank, there is a submersible pump, actually a borehole pump as it was all he could find.  This pumps water from the underground tank to a large, probably 300L or so accumulator (pressure vessel rated for potable water)  It then flows from there to the house.

 

The sumbirsible pump is operated from both a pressure switch in the expansion vessel and a float switch, so as long as there is water in the underground tank, it will charge up the accumulator.

 

This works very well indeed. You would think you are on a decent pressure and flow mains supply with always plenty of water on tap.

 

You do need some safety systems which were missing when I first met the system. The relay driving the pump had welded, so the pump just kept on pumping. The water in the tank was up to 12 bar, there was no over pressure relief, and pipe fittings in the house were starting to let by.  It now has a double relay system switching the pump and an over pressure relief on the pressure vessel.

[Nickfromwales]

4 hours ago, billt said:

This was installed the best part of 30 years ago and was an update to a much older system; a pressurised system was a remote possibility, but they were very rare in domestic circumstances, very expensive, potentially unreliable and very difficult to research. Also, mains power was much more unreliable then and could go off for a day or more (it still does very occasionally) - we don't want to be without water for several days thank you.

Ah, 3 decades ago yes, probably as good as it got back then . 

The beauty of the accumulator is that it stores at mains pressure. No electrical connection or reliance on power, no moving mechanical parts, one pipe in / out and if the power fails to the pump that's pressurising it, you keep getting pressurised potable water to the value of the effective / stored volume. Same exact scenario as you have, but clean fresh water. 

Agreed that as a modern solution it would be done according to what's available and the info / feedback used to arrive at such a decision, so please ignore my 'bad decision' comment as I thought ( assumed ? ) that you'd installed this recently. 

Oops  

[mike2016]

Thanks Folks,

Interesting discussion as always. 

19 hours ago, ProDave said:

Just what do you want your attic water tank to do.  If it is to provide the header for your how water, that's not just last century, the one before I think. Have you never been in a modern house and marvelled at the hot water coming out of the tap with the same force as the cold water?

 

In warmer climates they put the hot water tanks outside, but that would not work very well here in the winter.

Sounds like I've never lived in a modern house! The main reason I thought I'd need an attic tank is a buffer against mains loss and to provide a header. I have my doubts that I'll have space in the attic to fit one but that remains to be seen. Like the idea of a drip tray. 

 

16 hours ago, Nickfromwales said:

Ah, a guaranteed leak free system  ?

They don't make one I'm afraid as it's not down to the system it's mostly down to installer error.

Yes, components do fail, sometimes catastrophically, but more often than not leaks are caused by poor installation or incorrect fittings being used. 

When you go on holidays, turn the water off at the stopcock, simples . 

If your water pressure / flow rate is good, then IMO your about to unnecessarily increase your risks by adding components that you don't need. A 'tank' will give some redundant water storage, but an open tank won't be ideal for potable ( drinking quality ) water provision as I certainly wouldn't want to be drinking from a break tank when I've got cold mains available. Even more so if it's outside and the squirrels ( or worse ) start using it to give the kids swimming lessons . 

FYI, a "mains water tank" to me is a sealed accumulator, not and "open" aka "break tank". If you NEED an accumulator then it would be best off outside so it stays cold, rather than attain house ( ambient ) temp, and fitted in an outhouse or other frost protected location. The added benefit here is that if it ever fails the house stays dry, but, you can fit them in attics onto a drip tray to manage any drips etc. A stone resin shower tray would suffice for eg with the trap made off to an overflow pipe to outside. If there's a problem, simply engineer a solution.

My old boss used to say "If you're coming to me with a problem you should have waited a bit longer and be telling me the solution instead". In fairness we were usually in the middle of one ocean or another, so running to the merchants wasn't an option  

 

Best to first decide exactly WHY you want a tank before deciding what type and where it'll go. 

What, there's NO guaranteed leak free system out there?! We get about 1 - 1.5 bar when the mains water is running but they drop it occasionally to annoy us. I've never been in a house with anything other than an open tank . My current house has loose styrofoam placed over the tank as a cover, I bought a proper lid since and insulated the bugger. By the way, the squirrel finished giving backstroke lessons last Tuesday....I like the idea of a cold water accumulator, 300L sounds ideal....will look into an alternate location rather than the attic - why not ambient temperature though? I could put it in my shower I suppose but I don't think that's what you meant!! 

 

9 hours ago, JSHarris said:

 

We're also on a private supply, but rather than have a vented storage tank (lots of good reasons why these aren't a great idea) we have two 300 litre pressure vessels.  

How are the two vessel plumbed? In line or parallel? I plan on having separate hot and cold water manifolds too.....interested in how these are connect to the pressure vessels in your case? 

 

8 hours ago, MikeSharp01 said:

Yes, radial plumbing is the way to go if it can be arranged efficiently - IE put the manifold as close to the active middle of the system. (By active I mean demand led activity rather than run length as your kitchen taps will have many short duration demands while the showers will have occasional long demands and the bath very occasional very long demands and losses in these latter two from longer pipe runs are easier to tolerate, IE you can wait a little longer for the hot to come through, where as in the kitchen you want it NOW!.)

I'm building a small house and the manifolds will be nicely situated on the side of the house where all the taps/showers are. Good advice!

 

So I'm after a buffer mostly but want to ensure multiple points of use together don't cause too many issues. This is down to pipe diameter / pressure then? Thanks!  

[Jeremy Harris]

14 minutes ago, mike2016 said:

How are the two vessel plumbed? In line or parallel? I plan on having separate hot and cold water manifolds too.....interested in how these are connect to the pressure vessels in your case? 

 

They only have a single connection, so can only be plumbed in parallel.  Each 300 litre tank holds about 150 litres of water under pressure, as the compressed air behind the bladder uses about have the volume.  With a non-return valve on the mains inlet the accumulator(s) will charge to the highest available mains pressure during mains pressure peaks, usually overnight.

 

The outlet from the pressure tank(s) (really just a continuation from the tee at the base of the connection to it) works just like a cold mains input, but an a constant pressure until the tank(s) empty, when the pressure will drop to the incoming mains pressure.   It can split to feed both the hot and cold system, using a mains pressure hot water heating system, such as a combi boiler, UVC, thermal store or Sunamp PV.  The advantage is that the pressure is then the same at all hot and cold taps, which makes mixers work well.

[SteamyTea]

23 minutes ago, Nickfromwales said:

you keep getting pressurised potable water to the value of the effective / stored volume

Is it really to the stored volume or just the volume of the pressurised 'bladder' in it, so the usable volume will depend on the store pressure to a certain extent.

 

A pressure vessel is really only a header tank really, just one that can supply a pressure from ground level.

[Jeremy Harris]

The general  rule of thump is that the usable near-constant pressure volume from an accumulator is around 50% of the total stated volume.  The pre-charge air pressure has to be adjusted (using a tyre pump) to adjust for the operating pressure, typically it will be set to 1 or 2 psi below the max water pressure.

[Nickfromwales]

1 minute ago, SteamyTea said:

Is it really to the stored volume or just the volume of the pressurised 'bladder' in it, so the usable volume will depend on the store pressure to a certain extent.

 

A pressure vessel is really only a header tank really, just one that can supply a pressure from ground level.

Why I said effective  

A header tank is called that because it has to be at the head / top of a gravity fed setup. An accumulator can be mounted in a basement or garage etc. 

One is non-potable, and the other is 100% drinking quality, potable water.

Accumulators get size according to each instance, just like choosing between a 25 gal header ( CWS ) or a 50 gal one.  

[Jeremy Harris]

As I read the water regs, it's no longer legal to supply potable outlets (typically cold water to the kitchen) from an open or vented cold water tank, irrespective as to where the water comes from.

[SteamyTea]

What I don't like about fully pressurised system is that, by the very nature or pressure, everything is under a greater strain to start off with.

Then there is the need to have your installation fitted by a certified plumber, and the annual checks for your insurance, if you bother.

Then there is all the 'extras' involved, PRVs and other secondary safety devices.

 

Just seems a lot of work and kit really.

 

I do agree that shower pumps are noisy, but I am sure that can be mitigated with a slab of concrete and some rubber mounts.

 

If a header tank in the loft has animals swimming in it, then that is just a bad installation.  Not a problem I have ever had as I have always had the correct lid and extra insulation fitted.

[dpmiller]

why does a pressurised system "need" a certified plumber?

[Jeremy Harris]

2 minutes ago, dpmiller said:

why does a pressurised system "need" a certified plumber?

 

It depends.  A pressurised cold water system, like we have, doesn't require a Part G3 sign off, and can be done as a DIY job.  The same goes for a thermal store hot water system, if the thermal store itself isn't pressurised, and for a Sunamp PV; none need a Part G3 sign off or annual inspection.  You only need a Part G3 qualified installer, plus annual inspections, if you fit an pressurised, unvented hot water cylinder.

[Nickfromwales]

2 hours ago, SteamyTea said:

If a header tank in the loft has animals swimming in it, then that is just a bad installation.  Not a problem I have ever had as I have always had the correct lid and extra insulation fitted.

Thank goodness that rats and mice have blunt teeth and no desire to knaw through things