Ask The Trades - Moving my hot water cylinder

Phill in Skeg

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Moving my hot water cylinder
May 30^th, 2009, 8:42pm

I have a hot water cylinder just below my header tank in the roof of my bungelow. The how water pressure is pathetic and can take ages to fill a sink. I have had 2 suggestions: (1) put in a pump - the cold for the taps comes from a different header tank, also in the roof - can I boost just the hot water? (2) Move the cylinder downstairs to increase the distance between the header tank and the cylinder - will this help? Which is the better solution?

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thescruff

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Re: Moving my hot water cylinder
Reply #1 - May 30^th, 2009, 11:51pm

I assume you mean storage tank and not header tank, e.g. the tank that feeds the cylinder.

The pressure is the distance between the storage tank and the highest part of the system, so if you lower the cylinder you would increase the pressure to the next highest e.g the top of the cylinder or the pipework if they are higher.

Yes lowering the cylinder should increase the pressure, larger pipes would also increase the volume at the taps.

You can buy single pumps, but you need a minimum 600mm head for them to work, it would also be noisy if it was in the loft.

Need a bit more information on what you are trying to achieve.

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Phill in Skeg

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Re: Moving my hot water cylinder
Reply #2 - Jun 1^st, 2009, 12:06pm

Thanks for the info. Yes the cold water tank is the one I mean. It is just above the hot water cylinder. This is the highest point in the system. If I move the hot water cylinder, then the highest point would be the pipes that carry the water from the cylinder to the showers and sinks. But these would be lower than the current position of the cylinder.

When you say 600mm is needed for a pump to work, what is this distance please?

I am trying to get better flow out of the hot water to my showers and bathroom sinks and bath. The flow to the bath is so slow the water cools down before the bath fills!

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« Last Edit: Jun 1^st, 2009, 12:08pm by phillinskeg »

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thescruff Global Moderator Trade Member Author Offline Who said plumbing was easy. Posts: 6037 Total Thanks: 147 For This Post: 0 Gender: Trade: Plumber	Re: Moving my hot water cylinder Reply #3 - Jun 1^st, 2009, 12:42pm You need a minimum 600mm from the top of the pump to the base of the storage tank, normally it's not a problem if the pump is stood at the base of the cylinder. With low heads, it's also better to get a negative head pump that works on pressure and not flow. Salamandar make a couple of pumps that would be suitable.
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Headrush Trade Member Offline Ask The Trades Posts: 147 Total Thanks: 10 For This Post: 0 Nottingham United Kingdom Gender: Trade: Plumber	Re: Moving my hot water cylinder Reply #4 - Jun 3^rd, 2009, 6:11pm The height of the water in the cold storage tank is what gives you pressure at the outlets. To raise the head of pressure in a gravity feed system, raise the cold water storage tank. Build a platform in the attic and get it up as high as you can.
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CWatters Super Member Offline "Daddy fick it" says James Posts: 5150 Total Thanks: 58 For This Post: 0 Gender:	Re: Moving my hot water cylinder Reply #5 - Jun 3^rd, 2009, 8:40pm What he said. It's the height of the cold storage or expansion tank that matters. lowering the cylinder won't make any difference. The head in these two cases is the same...
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CWatters

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Re: Moving my hot water cylinder
Reply #6 - Jun 3^rd, 2009, 8:46pm

Quote:

I have a hot water cylinder just below my header tank in the roof of my bungelow. The how water pressure is pathetic and can take ages to fill a sink. I have had 2 suggestions: (1) put in a pump - the cold for the taps comes from a different header tank, also in the roof - can I boost just the hot water? (2) Move the cylinder downstairs to increase the distance between the header tank and the cylinder - will this help? Which is the better solution?

Do you have two header tanks in the loft? If the one supplying the cold taps provides sufficient head/pressure the simplest thing might be to use that one to supply the hot as well.

If the cold pressure is also very low perhaps consider switching to a mains pressure system. Before you do that someone must measure the mains pressure AND flow rate to ensure it's adequate. It's common for the cold tap on the kitchen sink to be connected directly to the incoming cold main. Is that noticibly better?

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thescruff Global Moderator Trade Member Author Offline Who said plumbing was easy. Posts: 6037 Total Thanks: 147 For This Post: 0 Gender: Trade: Plumber	Re: Moving my hot water cylinder Reply #7 - Jun 4^th, 2009, 12:53am Oh dear, the blind leading the blind
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runninwata GDPR opt-out Total Thanks: 147 For This Post: 0	Re: Moving my hot water cylinder Reply #8 - Jun 4^th, 2009, 8:55pm lol
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CWatters

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Re: Moving my hot water cylinder
Reply #9 - Jun 5^th, 2009, 7:34am

So only two of us passed their Physics O-Level?.... Grin

http://books.google.co.uk/books?id=97k3-VfkyiwC&pg=PA81&lpg=PA81&dq=physics+wate...

Quote:

The pressure due to a liquid is equal to the height of the liquid (h) times it's density (d) and g.
.
.
Liquid pressure is independant of the size or shape of the container, it depends only on the depth and density of the liquid

See below. The pressure at the bottom of all four columns is the same. If shape mattered the "extra" pressure in one would cause the water level in another to rise. It doesn't.

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« Last Edit: Jun 5^th, 2009, 7:51am by CWatters »

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thescruff Global Moderator Trade Member Author Offline Who said plumbing was easy. Posts: 6037 Total Thanks: 147 For This Post: 0 Gender: Trade: Plumber	Re: Moving my hot water cylinder Reply #10 - Jun 5^th, 2009, 10:15am No good posting fancy drawing which are wrong CW, Under stand the question and my answer
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thescruff Global Moderator Trade Member Author Offline Who said plumbing was easy. Posts: 6037 Total Thanks: 147 For This Post: 0 Gender: Trade: Plumber	Re: Moving my hot water cylinder Reply #11 - Jun 5^th, 2009, 11:57am Note the increase head.
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CWatters Super Member Offline "Daddy fick it" says James Posts: 5150 Total Thanks: 58 For This Post: 0 Gender:	Re: Moving my hot water cylinder Reply #12 - Jun 5^th, 2009, 6:03pm Ok so I oversimplified it. Try this one... note the constant head.
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CWatters Super Member Offline "Daddy fick it" says James Posts: 5150 Total Thanks: 58 For This Post: 0 Gender:	Re: Moving my hot water cylinder Reply #13 - Jun 5^th, 2009, 6:30pm It appears we differ as to the definition of "head". I assert that the pressure at the tap depends only on the distance from the tap to the surface of the water in the header tank. See also.. http://www.qpsltd.co.nz/pdf/hot_water_cylinder.pdf
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thescruff

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Re: Moving my hot water cylinder
Reply #14 - Jun 5^th, 2009, 8:31pm

The head is measured to/from the highest points in the installation, in the first example the pipe from the cylinder, in the second the same pipe on the loft floor, the head is increased by that distance.

For calculation purposes you never use the water level, as it drops as soon as you open and outlet, if you insist on boosting the figures then you should use the center line of the storage tank.

Time how long it takes to fill a small bucket stood in the bath from a shower hand set, then do the same experiment with the hand set at say 1m higher.

Do you want to tell qpsltd they are wrong or shall I Grin

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thescruff Global Moderator Trade Member Author Offline Who said plumbing was easy. Posts: 6037 Total Thanks: 147 For This Post: 0 Gender: Trade: Plumber	Re: Moving my hot water cylinder Reply #15 - Jun 5^th, 2009, 8:40pm Think about it in imaginary terms. We have a storage tank 10m in the air, therefor at ground zero we have 1bar. If I connect a hose to the end of the pipe, and walk it up the stairs, the higher I get the lower the pressure will be, until I get to the water level whereas the water will stop running.
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CWatters

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Re: Moving my hot water cylinder
Reply #16 - Jun 5^th, 2009, 10:31pm

thescruff wrote on Jun 5^th, 2009, 8:40pm:

Think about it in imaginary terms.

We have a storage tank 10m in the air, therefor at ground zero we have 1bar.

If I connect a hose to the end of the pipe, and walk it up the stairs, the higher I get the lower the pressure will be, until I get to the water level whereas the water will stop running.

You make my point for me. Looking at your diagram of the existing system... The dimension arrows suggest that the head doesn't depend on the height of the tap but clearly it does.

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