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PostPosted: Tue Mar 28, 2017 8:00 pm 
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We bought a house in the summer, and the 50+ year old boiler just gave up!! Its been condemned by British Gas and we've been looking at our options to replace. the current setup is a cold tank in the loft, hot cylinder in 1st floor cupboard and the old boiler in the ground floor utility.

We will be renovating the house in the next 6-12 months, so we want to put in the system which will ultimately work for a large 5 bathroom house... Also, my wife is slightly loony and wants a system that could potentially service 5 showers simultaneously!! (which i know is a tall order)

Anyway... after a quote from BG that was to just replace the boiler, we now have a company that has tested the pressure and believes we can install a Megaflow system - this is the potential solution suggested:

200L Accumulator
500L Ecotec Megaflow
637 Valiant Boiler (to service the Megaflow)
630 (TBC) Valiant Boiler for the heating

Other things to know...
- The heating system will potentially be a 10-15 radiators and underfloor heating in part of the house, at least 2 zone, possibly 3 zone
- The current cold water feed is an old half inch pipe from the street... this will be upgraded to a 32mm+ pipe when the renovations start, the current flow is 8L per minute and we're told it would need to be closer to 20L for this system to service multiple showers longer term


My understanding of this system is that the accumulator provides additional flow and pressure to both feed the Megaflow and the cold taps - hence, once the 200L has been exhausted we are reliant upon the flow from the Mains.

The 500L Megaflow should 'easily' accommodate the showers, but i presume it will be dependent ultimately on the pipes that leave the Megaflow? (i.e. we need to run a bigger pipe through the core of the house would be my guess.

I just want to understand if this is 'sane' and will give us what we want in the long term, i.e. multiple showers running at the same time without loss of pressure?

Many thanks for reading the wall of text and responding!


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PostPosted: Tue Mar 28, 2017 8:23 pm 
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A 200L accumulator will only store less than 100L boost. That won't do much with your 500L cylinder!

If you take a reasonable shower as 10LPM of hot mixed with 5LPM of cold then 5 showers will drain a 500L cylinder in ten mins - except they won't because after just over two mins the accumulator will be discharged and you'll only get 4LPM at each shower!!

If you really want that much hot water you will probably be looking at storing a lot more and using booster pumps.

I also would not separate the boilers as you suggest. If one goes down you lose hot water or heating.

The usual way would be to put the boilers on a low loss header and take the demands from the other side of it. That way the boilers can share duty or you can run one at a time during low demand periods. If one poops itself you will get enough hot water and heating to tide you over even during a cold snap

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PostPosted: Tue Mar 28, 2017 9:46 pm 
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WOW... thanks for the reply, a couple of questions if you don't mind:

- with the megaflow, my understanding was that it was a hot tank storage... hence, does why does it need to refill during the course of dispensing the hot water? i.e. why even bother with it, if it limits outflow the minute it doesn't have enough inflow...

- i don't really want to keep the cold tank, but it sounds like i would be better off keeping it and pumping to the boiler? or does it need to be pressurised?

- on the boiler side, sounds like it would be best off just going for two equal sized boilers, or does it not matter if one is 30kw and the other 37kw?


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PostPosted: Tue Mar 28, 2017 10:24 pm 
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As cold water from the incoming mains enters the Megaflo it forces hot water out the other end that's where it gets it's pressure from.

If the incoming mains isn't good you can't get much out of it. Using an accumulator can work if you have high pressure on the main but low flow rate but a 200L accumulator will not service a 500L megaflo it'll just run out very quickly and you'll have lots of hot water in the cylinder but not much coming out!

it doesn't really matter if the boilers are unequal but personally I'd fit 2 the same - easier to balance and there's always the possibility of swapping parts about in the event they both go down at the same time!

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PostPosted: Tue Mar 28, 2017 11:05 pm 
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Thanks again.

i don't understand why the plumber is recommending this solution when he measured the pressure this afternoon and told me it was low... i agree that the accumulator is clearly not going to suffice...

Can i ask where the boiler comes into the equation - i presumed it sat between the accumulator and the Megaflow, so rather than the Megaflow heating the water, the boiler does that? but your comment above suggests it the Cold feeds the mega flow... is the boiler heating the water inside the mega flow?

Last question (for now), does the accumulator need regular maintenance - I've looked a couple up and they have a 1yr guarantee and there is mentioned of replacing the diaphram.


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PostPosted: Thu Mar 30, 2017 12:59 pm 
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Sadly it sounds like you are being taken to the cleaners.

Flow rate in this situation is irrelevant it ain't gonna cut it.

What you should have by now is the static and dynamic pressure, without both you will be chucking several thousand quid down the drain. not that I would advise an accumulator anyway.

Assuming all 5 showers will be use simultaneously then you should be looking at 50/60 Ltrs/m.

You really need a plant room or large space at the back of the garage. 2 boilers connected properly (not Valiant) would be able to run a 500Ltr cylinder. then I would be looking at a twin pump set with a large storage tank and the megafow all in the same space.

Where are you located we may know a good guy/company.


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PostPosted: Thu Mar 30, 2017 4:09 pm 
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:withstupid:

Couldn't have put it better. :salute:

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PostPosted: Thu Mar 30, 2017 6:02 pm 
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Razor wrote:
:withstupid:

Couldn't have put it better. :salute:


Went passed your place at the weekend, was refereeing the World Billiards in Cambridge :thumbright:


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