Is a megaflo the right option?

[ajay88]

We have recently moved into a 5 b/room house (1910) and the plumbing system needs a complete overall. We currently have tanks in the loft and are looking at a megaflo and systems boiler as we may want to extend into the loft

We have good presure 3.2-3.3bar at street level and house. Flow rate at street is 20 l/min, at the house it is 10 l/min as our house is at a higher level than the street, the pipes are 1/2 inch iron

We are considering changing the pipes coming into the house and this may get us 18 l/min at the house as a guess.

Is 18 l/min enough, I see so many reference to 20 l/min, also as we're looking at aerated showers with say a showersave regulator (7.6l/min) so shouldn't the system work fine? (we'll have 2 showers in the house)

I'd be interested in any opinions or other options that we should consider, it's an expensive job so I want to ensure that we are doing the right things

many thanks
ajay

 

[Boilerman2]

Consider a Dualstream system which utilises a Hydronic Accumulator to support the incoming main this is linked to an Unvented Cylinder I would also consider a Twin coil cylinder which will be Solar Thermal ready!

 

[ChrisR]

If you can, change the mains pipe in the house to 22mm copper or plastic.
A Dualstream is an accumulator - you can use anyone's, DS's so- called "patent" is rubbish. Without an accumulator, or a pump from your tanks, you would expect to notice a change in flow when a second tap is opened. You'd probably get used to it, but it's not ideal.

Accumulators are expensive, and need to be as big as the water store, but they are trouble free and quiet.

 

[tamz]

As Chris said the most important thing is to renew the supply pipe, upgrading to 25 or 32mm MDPE and get the water authority to give you a new connection.
Forget the accumulator and just do it right.

 

[Alfredo]

I was on a Viessman course last week.

Their system boiler can operate on four pipe with dedicated pipes to unvented cylinder. The clever bit is the plug in thermistor instead of using a cylinder stat which enables the boiler to modulate in response to thermistor values instead of just being in on/off mode on a stat. The only 'neg' is they say you have to use the Viessman cylinder as this is the only one with a thermistor pocket..theirs is made by Gledhill, but is badged Viessman and the normal Gledhills don't have the thermistor pocket.

They also have plug in weather compensation (controversial on here) for the boiler. They say it works...

I know...I've sold my soul for a Polo shirt with Viessmann on it but it sounds quite a good setup to me, and you can link all their solar stuff in as well, but we didn't go into that.

Alfredo

 

[Agile]

Viessmann never gave me a polo shirt!

Its the dynamic flow rate which is important, not the open pipe ( apart from indicating that its not enough ).

I would want 22li/min at 1.0 Bar to be happy that its going to perform properly.

Anyone without a 25mm supply pipe is likely to be disapointed!

Tony

 

[ajay88]

Thanks very much,

we will definitely be getting the pipe upgraded to 25mm, personally if I can avoid getting an accumulator i would be much happier, space is certainly a problem and i still need to be convinced about the extra cost

maybe the compromise i sa large combi, maybe valliant 937 or similar as this would probably have a similar performance to a megaflo but at less cost, the accumulator maybe the perfect answer if we can manage the cost and space

cheers
ajy

 

[powell30]

NO combi will give a megaflo a run for it's money IF the supply/domestic side is set up correctly.

Forget the combi and fit unvented correctly and you won't be disappointed.

 

[oph]

One thing thats often overlooked with UV cylinders is working flow rates whilst more than one tap is open.
From experince in my own place, consider this......

 

[Agile]

I think that it will still be subject to the G3 regs because its pressurised.

The Viessman 200 series allows direct modulating control of the boiler according to the temperature in the cylinder. How much that saves is a matter of opinion and mine is that its likely to be less than 15% but that depends entirely on how its set up.

In some installations if the flow temperature is kept at about 70° and the flow rate adjusted to give 20° diffferential then it could well save 15% compared with a flow temperature of 70-80° and a differential on just 10°C.

Tony

 

[ajay88]

once again, thanks-

also due to the fact that we live in a very hard water area and the many comments above a megaflow certainly seems the right way to go, we will certainly be changing the incoming pipes and may or may not go for an accumulator,

cheers
ajay