# Water pressure

It might sound a silly question, but - If I connect a pressure gauge to the cold water tap in the kitchen sink and turn the tap on full, will that give me a measure of the mains water pressure? The kitchen is on the ground floor and fed directly from the mains. (I don't want to spend £2000) on a combi boiler only to find it won't work!
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On Mon, 16 Oct 2006 00:34:33 +0100, "Frank McGuire"

Find how long it takes to run 12 litres of water from the kitchen tap.
If under a minute, a combi with that flow rate will work.
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Frank McGuire wrote:

It will, but that does not actually tell you much of use (other than you have enough static pressure to exceed the minimum required by the boiler (often 1 bar).

You need to measure the flow rate, by timing how long it takes to fill a container of known size from the fastest flowing tap in the house.
Under 10 lpm - no hope. 10 - 15 - too low unless you are fitting a low power combi (i.e. under 30kW) and will only even need one tap at a time
15-20 is better - but still not great. Over 20 is usually adequate.
A reasonable combi (say 35kW) will be able to manage about 15 lpm of water at a usable temperature. So if the supply can manage 25 lpm that should prevent the shower stopping when someone flushes the loo, or the dishwasher decides to fill.
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Cheers,

John.

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John Rumm wrote:

But are you fitting the boiler in the kitchen? NB if you're fitting it upstairs, say, the flow rates could, and probably will, be very different...
David
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Lobster wrote:

Don't think it makes much difference does it? The static pressure seen by the boiler may be less by about 0.3 bar or so. The total length of pipe from mains to tap is much the same and the sizes of pipe also the same.
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Cheers,

John.

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May well be quite a few elbows though - they slow the flow down quite a bit.
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Skipweasel
Pay no attention to that man behind the curtain.
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Guy King wrote:

Well I assume you will have much the same pipe layout wherever you place the combi, be it near to the start in the kitchen, or near the tap in the bathroom. The total quantity of piping, bends etc will be about the same, so the total flow resistance ought to be the same.
If the flow is marginal then it is worth using swept bends and bigger pipe.
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Cheers,

John.

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In theory; yes! The pressure gauge should be connected directly to the tap. Most kitchen taps do not have the external thread for connecting a hose though - unlike external garden-hose taps. FWIW; manufacturers seem to cite 3 Bar as the optimum pressure , Please be aware that pressure and flow, albeit interconnected, are different aspects you'll still need the flow of 12 lts per minute.(?)

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Brian

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Yes, but it won't tell you anything about the flowrate.
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Skipweasel
Pay no attention to that man behind the curtain.
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That's alot of cash - is there alot of re-plumbing involved?
Charlie
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Sorry, it's 2000 euros - I'm in Ireland - about 1250 sterling.
It'll be an exteral combi (Grant) located on the ground floor just outside the kitchen. When I connected a gauge to the tap it reads about 2 bar. I haven't checked the flow rate yet but I will at the weekend.
What about booster pumps? Would one of these help?
I'm thinking if I install a cold water storage tank(fed from the mains) alongside the boiler, and connect it to the boiler via a booster pump, would that work? Obviously there wouldn't be much pressure coming out of the tank since it's on the ground floor, but would a booster pump suck enough water out of the tank to feed the boiler?

That's alot of cash - is there alot of re-plumbing involved?
Charlie
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