Unvented system with 15mm mains supply?

24 l/min should be ok, but it sounds like your static pressure is not as huge as you think it is.
You want a good 3 bar minimum.

Normally, minimum supply pipes would be 25mm into the house and 22mm internally.
Anything less and it may not work.

The fact that your flow rate drops off dramatically when you open more that one tap says it all really........

 

GIF is probably right the only way your going to find out for certain is to have a G3 installer do a survey and carry out the nessacary tests, but from what you have said an upgrade is probably the only way

 

Chances are you will be ok - unless you have prolonged showers.

The whole purpose of an unvented cylinder is to store hot water at mains pressure (well, regulated to around 3 bar, I understand) and with a compressed air vessel inside so that it will deliver a full flow at 3 bar via more than one outlet at a time.

The bulk of this flow will be delivered by the compressed air vessel, but it will also be replenished to a considerable degree by the incoming mains.

You will (should) have used up all your stored hot water in any case by the time the actual flow is also petering oot.

But, best to have a G3 confirm.

 

I'm DIY, so forgive me if I've got this all wrong, but...

You currently have a vented cylinder, so doesn't that mean that it's currently fed by a cold water tank, rather than mains??
Maybe I'm wrong on that thinking, but if so what's the problem?

My situation is that my mains cold comes into the house in 15mm and feeds cold tank in the loft.
This is sufficient to feed two separate gravity fed showers at the same time.
Of course, running out of hot water is a different issue! But there is no problem with the strength of flow.

Again, my apologies if I've got this all wrong!

Regards,

Cando

 

That's fine

Just check with manufacturers literature

Normally you can go as low as 1.5 bar, flow rate is super,

You need survey

 

Hi BB.

Time to do your own research .

Contact manufacturers of unvented systems and ask their opinion. Of course, you should really have some concrete figures for your incoming flow and pressure first - any chance of getting these figures? (Flow is dead easy, pressure requires a gauge.)

Do you understand the basics of an unvented cylinder? That's all I know - just an outline of how they work and what they do.

Based on my limited knowledge, the first important point is that they don't rely on the mains input for their output! Ie - if you shut off the mains stopcock, the cylinder would still deliver a full hot water flow to your taps.

This is because they have a squishy balloon inside the tank, one that becomes compressed as the cylinder is filled by the incoming cold mains. Once compressed - to around 3 bar - this balloon will provide the real pressure behind the flow to the hot taps - it will shove out that hot water at a terrific rate if required, more than enough for 2+ taps/showers.

Of course, it then relies on the incoming mains to keep that cylinder 'topped up', but the incoming doesn't have to match the outgoing; the cylinder has this built-in reserve.

I reckon the worst case scenario - if there is any doubt that your 'huge' demand will 'outrun' the 15mm supply pipe and it can't keep up - is that you'll chust need to fit a slightly larger volume unvented cylinder. That will then have the reserve you'll require so you can shower away happily - you'll be able to have 2+ showers running at the same time and can run - stark bollocking naked - in between them.

Not that I'm picturing nuffink, of course...

 

What the hell are you talking about DA. It won't deliver any more than a release of pressure and nothing more, its the in coming cold main that pushes the hot water out The squishy ballon as you call it is to take up the expansion from when water is heated as it expands.
Please do not offer advice on something you clearly are not qualified to offer or even have a clue as to what your talking about. I can see now why G&W gets frustrated with some of the responses on this forum.

 

It's this simple

A cylinder has less restriction to the supply,

Example

- combi 14 ltrs/min
- cylinder 26 ltrs/min

There's lots of other factors that need to be considered for correct operation too

DO NOT let someone fit it untill they can provide written performance criteria.

If a plumber suggests "fit it and we'll find out"!...then He's a total idiot

Lots of Unvented engineers don't always have the ability to see beyond the airing cuboard so you need to ask for a technical explanation for their proposal and insurance of it working correctly.

If you don't mind, what area are you from?

 

There's many solutions,

An exp vessel is just for hot water expansion, it's 10% of the cylinder capacity

 

I can do Essex

"If you think I'm expensive....wait till you hire an amateur"!!!!

 

Evening Bargain Bucket, if you're local to Plumpton Green I'll happily call round and check your pressure and flow rates for you on my way home one day!

Unfortunately I'm one of those who is booked up for a few months but at least you'll have some figures to mull over and make an informed decision!

 

There's your man

 

Finally joined the forum just to offer my good deed for the day

And yes I'm G3 and Gas Safe....not touting for the work though just happy to offer some free local advice!

 

Ahhh, shame it wasn't a week ago as I was fitting a boiler there then! If it can wait till the end of June I'll be back there to do their bathroom but I suspect you'll have had it done by then!

 

Iv

I finished 4 flats in Eastbourne just before Christmas, use to be a pub, next to a bowling green, Sainsbury's below it