Pressurised hot water tank

Hi there.
We are planning to fit a new bathroom. At the moment we have a shower off the taps over the bath (we have a normal gravity hot water tank, GCH) and the hot water pressure is not great but sufficient. We were advised that a pressurised hot water tank would drastically improve the pressure (and also increase the CH efficiency). Is the difference really worth the cost (we were quoted around 1000 for supply + Installation) ? Would a good electric shower do the same job ?
Thanks in advance for your help,
Bertrand
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They are costly to install but do produce great results BUT only really if you have good cold water pressure, because the cold water provides the pressure going into the hot water system. A good electric shower would be rubbish at best. What cold water pressure do you have? I measured mine using a bucket and at my last house (where I had a pressure system) I was getting arounf 20 litres per minute. This gave me a fantastic shower.
Cheers Mike
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Hello,
Thanks for the reply. I just measured the flow and get at least 20 l/min, so I guess it would be worth. What about the price: does 1000 for supply + installation sound reasonnable ?
Thanks !
Bertrand

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If your main concern is for the shower, then get one of those Venturi showers where the cold water provides the pressure to drive the hot water through (or something like that). Argos do one for 70, cat no. 830/4131. B&Q also stock the same model in various finishes. Gives me a far better performance than any electric shower I've ever used, it's much cheaper to run (I'm on Economy 7, so I heat up the water during cheap rate) and is pretty straightforward to fit (although I paid a plumber 100 to put mine in).
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On Sat, 8 Nov 2003 10:17:50 -0000, "Bertrand Collet"

In principle I would have thought so. Depending on the environment, fitting a new cylinder is fiddly.
I would ask what make and model of cylinder he is proposing and check the price separately yourself.
.andy
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On Sat, 8 Nov 2003 08:36:45 -0000, "Bertrand Collet"

There's a mix of questions here.
It's important to appreciate the difference between flow and pressure. The two are related but pipe sizing etc. is important. For example, you can have a good mains pressure measured statically with no taps turned on, but because the service pipe from the road is perhaps too small, when the taps are turned on, the pressure drops dramatically an the flow is not great. Typically it depends on the property. Older places tended to have as little as 1/2" lead pipe because predominantly, it was to feed a tank in the roof. Newer places have progressively larger services with nowadays 25mm or more being common. Behaviour will also depend on where you are located and what the water supplier does. By law, they are only required to provide a fairly paltry flow rate of 9 litres/min at a cold tap near the incoming main.
You can easily have a situation where you have a good pressure if the flow rate is low, but as soon as you want decent flow or multiple things running, may prove woefully inadequate.
To get an idea of the situation, measure the flow rate at the kitchen cold tap using a measured container like a bucket and a stop watch. If you are getting 20 litres/min or better then the rate will generally be respectable for a pressurised HW system. Less than this is questionnable IMO. For a decent shower, I think that 15 litres/min is appropriate.
The instant electric showers do about 4lpm and are fairly disappointing as a result.
So a pressurised system is good if you have a good mains water supply. Also, consider whether you want to have more than one thing running at a time. There are ways to share the flow with flow restrictors and other means, but ultimately the mains has to be able to supply the requirement.
A roof tank does have the advantage of providing a store of water at all times, and there is no issue with running as many things as you like. To do this, you can run multiple cold services directly from the tank, so typically for a shower the cold is run from there and the hot from either an additional tapping on the HW cylinder or a device like a Surrey flange which allows connection of an extra HW take off pipe into the existing tapping. Shower pumps work well and can easily deliver 25 litres/min of water at good pressure or a lower rate at a high pressure. It is worth buying a good one like a Stuart Turner because they last longer and run quieter than the cheap products. If that's what you meant by an electric shower, then yes, they do a good job.
A pressurised cylinder won't make the CH more efficient. However, it is possible to get fast recovery HW cylinders, both sealed and vented. These have more coil heat exchanger inside and can allow the boiler to transfer heat at a greater rate. It is common to have HW priority, which means that when it is required to heat the water, the boiler is switched over to it exclusively. Obviously the shorter time that is the better. Not a definition of efficiency as such, but I suppose some might describe it as that.
.andy
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wrote:

When using a power shower pump, the tank may also be exhausted of water if it pumps at high rate and other draw-off are on. The tank size has to be assessed for suitability.

Quick recovery coils make the boiler more efficient.

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Bertrand Collet wrote:

As an alternative, have you considered putting in a good quality power shower pump?
I plumbed one up in the airing cupboard (sat on the shelf next to the tank.
Run the flow pipes into the loft, across, then down a channel in the wall to a propper shower tap thing.
Best shower I have ever used.
Only downside was only having a shower curtain meant the updraught would cause the curtain to be magnetically drawn to ones wet body.
Pump cost about 200 IIRC.
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Bertrand,
Don't bother with these. Fit a heat bank. They have far more advantages than unvented cylinders and work off the mains. Heat banks work on low atmospheric pressure, cost about the same, eliminate tanks and "overflows" (these have to be 28mm with unvented cylinders) and they can be DIYed. Unvented cylinders need a BBA approved plumber, who charge the earth.
Do a Google on uk.d-i-y for "pandora" http://www.heatweb.com For an explanation of heat banks.
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Yes it is, provided the thought of 1000 doesn't make you squirm. They cost about 750 quid inc. VAT supply only. They are absolutely excellent. The only other choice that comes close is a heat bank. These get almost as much flow rate (about 40 litres per minute) as an unvented cylinder and don't require annual servicing to test the safety valves. Cost will be similar, but you may find it difficult to find an installer who has heard of them. They're an easy DIY job if you can do plumbing.

Absolutely not. Depending on your mains flow rate, an unvented cylinder is capable of around 70 litres per minute. An electric shower is capable of around 4 litres per minute. An average combi boiler can manage around 12 litres per minute. A good shower is around 10-15 litres per minute. Having more than 15 litres per minute from your system allows two showers simultaneously, or can fill a bath much quicker.
Christian.
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