Installation of System boiler above unvented cylinder

[andyman22]

I'd appreciate any help with the following, though realise it's limited info.

We have a small utility room, and are upgrading our boiler. We're thinking of going for either a large combi storage (Viessmann 222) or potentially a system/unvented cylinder approach.

The question is, is anyone aware if its possible or even advised, to install a boiler above an unvented cylinder. Guessing this makes maintenance harder and not sure on safety. Looking at an example of the Viessmann, I notice a 210l cylinder is 1500mm and the boiler is 850mm. Ceiling height is 2.7m. With flues etc, is this going to be too cramped?

Not stuck on Viessmann, but quite like their weather compensation and control system. We have 3 zones, so it seems not many of the other control systems would work (Wave, Vailant etc).

Any help appreciated.

 

[muggles]

There's absolutely no reason at all why you shouldn't put a boiler above an unvented cylinder. Combi storage is a hashed compromise and I'd recommend separate units if your mains is up to it. Have a look at Intergas - you can have your weather compensation, you can have hot water boost so that your cylinder reheats quickly but your radiators are run at a cooler temp to save gas, and you can use an OpenTherm control system such as Honeywell Evohome which will reduce the temperature of your radiators in proportion to the room temperature, thereby reducing gas bills further and keeping the room temperature more constant. Also a very good boiler with up to a 10 year warranty available

 

[ServiceNumpty]

You might be limited on cylinder size, 150/170ltr will probably be your max size. To allow all servicing clearances to be met for boiler.

 

[andyman22]

Thanks both for the info.

Looks like I'll need to speak to the builder to see if there's a better way of doing this if possible. Between 4-6 people staying at the house so a 150l maybe a bit too on the small side. Presuming there's no problem with having a boiler further away from the unvented cylinder, approx 8m?

 

[muggles]

Buy a Joule branded cylinder - they do shorter, 600mm wide versions that will allow you to have the boiler above it and have the capacity you want. For example, a 200L will be 1150mm high, a 250L will be 1400mm high and a 300L will be 1600mm high. You can even have a 400L at 1570mm high, if you've got space for a 710mm diameter cylinder

 

[andyman22]

The plumber had mentioned that the 222-f was essentially an integrated boiler and unvented cylinder, though you mention it's a compromise. Is this not what it is? Kind of thought the water store was like an unvented cylinder with mains pressure and then it could switch to combi mode when it ran out...

 

[andyman22]

Excellent, thanks for the cylinder idea. Will have a look at them.

You don't happen to know about the question above, about whether the 222 is actually equivalent to an unvented cylinder?

 

[muggles]

You don't happen to know about the question above, about whether the 222 is actually equivalent to an unvented cylinder?

It's a half-way house. You'll be restricted to 20 litres per minute flow rate on hot water, so if your mains is capable of more than that then an unvented will still be the better option. Once the store is depleted the flow rate will drop off dramatically until the boiler has an opportunity to re-charge the store (IE a period when you're not using hot water)

http://www.jouleuk.co.uk/wp-content...e-Stainless-Solar-Heat-Pump-Brochure-2016.pdf

 

[andyman22]

Any idea why its restricted to 20 l per minute? I thought as it was just a cylinder there shouldn't be a restriction on it coming out at near mains pressure? Realise I'm missing something here!

 

[muggles]

The store on the 222F is only 130 litres. They make it up to 200L usable hot water as the boiler fires to reheat the cylinder as soon as hot water starts to be drawn, but the boiler doesn't keep up with demand even at a 20L/min flow rate, hence you get a reduction in performance after a time. If they allowed a higher flow rate, you'd get a smaller total usable volume of hot water as the store would run out faster and the boiler wouldn't be able to reheat it fast enough

 

[andyman22]

Ah, with you now, its been an educational morning for me! Thanks for your help on this thread and the other, much appreciated.

 

[Phill Peck]

Haven't read all posts but I would go with a system boiler and invented over a 222 any day.
I am a Viessmann installer btw.
What id recommend is a Viessmann system boiler on 4 pipe which will give you endless hw if combined with the correct cylinder.
A 222 is basically a Viessmann system boiler sitting on top of a unvented cylinder but more expensive and harder to maintain

 

[andyman22]

Thanks. Is the advantage of the 4 pipe that there's less components and it can switch easily between the modulation for CH and quicker DHW heat?

 

[muggles]

Thanks. Is the advantage of the 4 pipe that there's less components and it can switch easily between the modulation for CH and quicker DHW heat?

That's the idea.

@gasservice1985 quick slightly irrelevant (to this post) question - in all the online literature it says LPG models require 50mBar gas pressure. Does that mean Viessmanns can't be fitted on LPG in the UK, or is there a workaround?

 

[Phill Peck]

Thanks. Is the advantage of the 4 pipe that there's less components and it can switch easily between the modulation for CH and quicker DHW heat?

That's the idea.

@gasservice1985 quick slightly irrelevant (to this post) question - in all the online literature it says LPG models require 50mBar gas pressure. Does that mean Viessmanns can't be fitted on LPG in the UK, or is there a workaround?

No idea mate I don't do Lpg. Very little requirement for it round here