Mole a new water main or fit combi and fit accumulator?

We really do need to know the static pressure.

Then the dynamic flow rate which you can take whilst leaving say 1.0 bar in the pipework.

That is needed to operate any shower properly.

An unvented will not perform so well with less than about 22 li/min @ 1.0 bar.

That will operate one good high flow rate shower or two average showers.

You have said nothing about how many live there. That's needed to design a storage hot water system.

Sponsored Links
What would you prefer to call it then Dan?

Morning all

Beautiful morning here.

Agile - many thanks.
Yes I can see the static and dynamic pressures are crucial, but how would I measure the static flow,other than what I did already?
ie measuring at garden tap and showing results above, & attempting at washing machine and dishwasher.

No of people: There's 2 adults and two muddy little boys.
Sponsored Links
There is no such thing as static flow!

You need to measure the flow rate that you can get whilst still having 1.0 bar left in the pipework so that it provides adequate pressure to operate a shower head.

Generally 22 litres/minute is the minimum to get a good benefit from an unvented cylinder.

Perhaps I have missed the results but don't see any meaningful data quoted yet.

The pressure gauge should show the static pressure when no flow is taken and that pressure will reduce as you increase the flow rate.

I use the rule of thumb for sizing an unvented cylinder of 50 li + 50 li per person.

So in your case 250 litre unvented.

Many will suggest a 200 li cylinder but the installation cost is the same so I would say its better to size it properly as the additional cost is minimal.

Many don't understand physics and think they waste energy heating up more water in a larger cylinder. But this is a fallacy as they are very well insulated and only lose 1-2 kWh of heat a day. Better to have them well sized rather than to run the risk of running out of hot water.

Agile, ha ha static flow. Clearly too early in the morning for me not to be and make an oxymoron. :oops:

Moving swiftly on... thanks for the guidance on cylinder size.

I will try the dishwasher connection to measure the static pressure.
There's something very odd going on with those readings...the pressure should drop as you open the kitchen Dan mentioned it's the non-return valves in the outside tap....and there's perhaps a pressure spike ramping up the pressure to 8 Bar.

Assuming there's no double check valve on the supply pipework to the outside tap you could unscrew the tap and screw the gauge into the wall plate.

Alternatively if you leave the gauge connection onto the tap a little loose ie..a small dribble of water is allowed on the connection, then this should be sufficient to keep the non return valves open to give a reading.
Morning all

OK we have new pressure measurements, which seem to be more normal.

Under the kitchen sink, with pressure gauge attached to the outlet for dishwasher, I got

That outlet alone: 4.4bar (is this the static pressure?)

With kitchen cold tap open as well: drops to 3.2bar
With all cold taps open (kitchen , cloakroom tap, bath, basin): 1.6bar.
(are these the dynamic pressures?)

Shower was not open though as that is pumped so I thought might be a confounding variable.

-potentially 2 bath, 1 shower
-unlikely to be all used at exactly the same time though
-2 adults 2 kids.

Mole quote £630

SO, in terms of which boiler system would be most suitable, whilst maintaining good pressure at showers if you open the kitchen tap, what would you recommend?
System types?
Brand and size?

Many thanks.
Yes 4.4 bar is the static pressure ie. it's the pressure with no water being drawn and it indicates the pressure in the street main. 4.4 bar is good, round here you're lucky to get 1 bar.

You say the pressure only drops to 3.2 bar with the kitchen tap open with a flowrate of just 7.5 litres/min and with 4 taps open it drops to 1.6 bar. These pressures are dynamic or working pressure readings.

However, with your traditional setup it would be more normal for only the kitchen cold tap, garden tap (and often washing machine/dishwasher) to be directly off the mains. All hot taps and other cold taps will be fed via the cold water storage cistern. We only want to measure the pressure/flowrate associated with the mains water supply.

You need to ascertain which cold taps are fed off the mains...perhaps the cloakroom is also connected. Sometimes the plumbing is botched and bathroom/basin taps are connected to the mains. Check the pressure by placing you hand over the outlets.

Are you sure you're calculating the flowrate correctly? If you're using a Weir gauge chuck it...many are very inaccurate. A bucket and measuring jug is best.

I think your kitchen tap has either the isolating valve partially closed or a strainer/aerator is blocked....I would expect the flowrate achievable to much higher at those pressures.

Garden tap non return valves are often broken leading to lower than expected it too should flow higher.

So ideally you need to open all cold taps (including the garden tap) and measure the flowrate at each outlet (whilst all cold outlets are open).

Report back the total flowrate and the pressure at that flowrate.

If you can get sufficient flow to drop the pressure down to 1 bar that will give a good indication of the performance....since showers and 1/4 turn taps require that sort of pressure to perform well.
Upstairs and downstairs basin are low pressure, so I assume from the loft tank, so I'll ignore them.

So I need flow rate at each of
Kitchen Tap
washing machine
garden tap

whilst all of these are open ?

ps (are you trying to flood my house?!!)

You're trying to measure the flowrate when the pressure drops down to say 1 bar so as to give a flowrate reading when the pressure's still adequate to be of use.

In a traditional cistern setup you might have a 30 litre/min flowrate from an old 3/4 bath tap but due to the height of the cistern in relation to the tap (ie. the pressure) it could be totally unsuitable for a shower. Your own property may only have a pressure of say 0.25 bar (2.5 meters water height) at the bath tap..hence the need for the pump.
Aiming for around 1 bar (a 10 meter water height) ensures an adequate pressure for showering. So we want to know what the flowrate will be at that pressure..and whether it's sufficient to run multiple outlets whilst still at that pressure.

At the moment it would appear that both the kitchen tap and garden tap have problems as the flowrate appears to be too low given the pressures you quote.

You need to see why the flowrate from both these taps is so low...are the check valves/strainers failed/blocked, is there a partially closed service valve etc. Outside stopcocks often have 2 check valves that are prone to failure from frost damage..sticking shut or partially closed.

There's no point in considering an upgrade to the service pipe until a correct flowrate has been established.

You didn't mention the bath tap...I'm guessing this is off the cistern so should be ignored. Yes the flowrate must be the total so ALL mains pressure taps should be open at the same time whilst measuring each individual tap flowrate.
Okey Dokey

Bath tap from the loft cistern.

SO ignoring that too, we have washing machine and dishwasher inlets, kitchen tap and garden tap on mains pressure.

With kitchen tap, garden tap and dishwasher open, the dishwasher give 10lpm
With other 3 open, the washing machine gives 6lpm
With other 3 open, the kitchen sink gives gives 1.5lpm
With other 3 open, the garden tap gives 4.5lpm.
So a total of 22.

You need to see why the flowrate from both these taps is so low...are the check valves/strainers failed/blocked, is there a partially closed service valve etc. Outside stopcocks often have 2 check valves that are prone to failure from frost damage..sticking shut or partially closed.

Sorry I don't know what check valves/ strainers / service valve are.
Our stopcock is in the kitchen so no frost damage there. I don't know about the one in the road.

There is a another tap visible under the sink - it's jammed and I don't know what it's for or even if it's open or shut. I can post a pic. Maybe that's the culprit.

Do the flow rates I measured help suggest the best heating system?

Many thanks.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links