2 combis vs one Megaflow help!

[Madrab]

But are they a bad idea?

No - they have been serving houses for decades and decades without any issue at all. The issues though are with all the modern fittings and fixtures, outlets, appliances and then the clients requirements etc is, as you have seen, the flow and pressure from an open vent gravity HW cylinder isn't suitable and that's where the pump comes in. Don't forget the cold water cistern(s) in the attic will create significant noise when filling and that may affect your decision to retain them when the loft is converted.

If you are happy to work with a HW system pump and the noise that comes along with that and ensuring that the cylinder is setup and configured/and laid out properly, it can work very well. 1000's of people use that setup quite happily today and it can be serviced by individuals without the need for extra quals.

 

[JimCrow]

You want an experienced central heating engineer that has his grounding as a plumber and don't be shy in asking what level they are qualified to. You are looking for them to tell you (don't offer them the info) they are min qualified to Level 2 and Level3 C&G in plumbing & heating and for you have their their DHWSS (G3 UV) qualification (water regs would help too), that way you should get a qualified plumbing and heating Pro who has completed their advanced hot and cold water systems, has a min of on the tools exp, is qualified to fit and service unvented cylinders and should be well versed in everything the pro's here have been suggesting.

If any professional balks at you asking to confirm (show you) what level they are qualified to, then walk away. I'm chuffed when a client asks to see my quals, I spent a lot of time and effort (and money) obtaining it all and more than happy to show it off if it makes a client more comfortable.

Our trade, unfortunately, is plagued with wannabees, have a go hero's and/or CH boiler chuckers who think they know what they are talking about and cause more problems than they fix. Oh and ask them to confirm how much they are insured for and what they guarantee. You have a lot of work to get done and it won't be cheap, this way you are at least trying to safeguard your investment.

When your clients asked to see your plumbing qualifications, what did you show them to keep them happy?, I recently retired with over 52 years at this game and I have never been asked once.

 

[VioletG]

Rsqaa

No - they have been serving houses for decades and decades without any issue at all. The issues though are with all the modern fittings and fixtures, outlets, appliances and then the clients requirements etc is, as you have seen, the flow and pressure from an open vent gravity HW cylinder isn't suitable and that's where the pump comes in. Don't forget the cold water cistern(s) in the attic will create significant noise when filling and that may affect your decision to retain them when the loft is converted.

If you are happy to work with a HW system pump and the noise that comes along with that and ensuring that the cylinder is setup and configured/and laid out properly, it can work very well. 1000's of people use that setup quite happily today and it can be serviced by individuals without the need for extra quals.

Thank you. If I did that, kept the one vented cylinder , so it does the whole house. Is it a major job to go unvented at a later date?

 

[dilalio]

Rsqaa

Thank you. If I did that, kept the one vented cylinder , so it does the whole house. Is it a major job to go unvented at a later date?

You will need a discharge pipe for a UV.
And if putting a vented cylinder in the loft, your cwsc needs to be above it.

 

[Madrab]

When your clients asked to see your plumbing qualifications, what did you show them to keep them happy?, I recently retired with over 52 years at this game and I have never been asked once.

A pic of my C&G quals, my Water Regs, DHWSS, GS ticket and a pic of my insurance cover - only been asked a few of times in my 30 odd years mind you and they were in larger properties where the costs were going to be significant.

Sign of the times I guess, clients are becoming more educated about what pro's should be qualified in and they want to see the evidence of that before deciding to go ahead, as there are far too many shysters out there ripping people off these days that .

 

[VioletG]

You will need a discharge pipe for a UV.
And if putting a vented cylinder in the loft, your cwsc needs to be above it.

Thank you. We would keep the vented cylinder in the bathroom, the water tanks are above it in the loft.

We currently have two Vaillant ecoTec Plus 412 boilers. So am I right that we would need to upgrade this to power the whole house?

From what I have read on this thread, downstairs should then be OK with pressure without a pump due to the tank being higher up but we will need the pump upstairs.

The Vaillant website seems to make it sound easy to switch over from the vented to non vented with their Unistor systems.

 

[Elsa TLC]

An horizontal unvented cylinder fitted with maintenance in mind in the loft is the way to go.

Make sure that the loft is lit up well and boarded. Safe to work.

Also fit a secondary return (15mm copper.) With a copper (ideally) 22mm hot water feeding the house.

Be sure to ballance the cold water

All pipework insulated well in loft and your a winner.


Key to all the above as said is a good mains cold water supply..

 

[Elsa TLC]

When your clients asked to see your plumbing qualifications, what did you show them to keep them happy?, I recently retired with over 52 years at this game and I have never been asked once.

I'm not sure I could reel off my Q's on the spot. But I wished people would ask. As there really are some shocking push fit plumber alikes out there.

 

[Elsa TLC]

Rsqaa

Thank you. If I did that, kept the one vented cylinder , so it does the whole house. Is it a major job to go unvented at a later date?

You'd be spending over again. Just do it right now.

If possible work from top to bottom in regard to the whole renovation.

Do it well do it once.

 

[Madrab]

An horizontal unvented cylinder fitted with maintenance in mind in the loft is the way to go.

It is rare I disagree with other pros on here but unfortunately in this case I cant agree - horizontal cylinders - OV or UV - are a complete waste of time and money IMO and are really the last resort when it comes to HW storage.

The reason for that is, a HW cylinder's fundamental design is to heat at the bottom section and then convection heats the water above and so on till it heats the whole cylinder hence it's design as a vertical cylinder. It then creates stratification layers stopping the cold inlet from mixing and cooling down the heated water altogether a pretty efficient design.

Turning the efficient vertical cylinder design on its side completely changes those design pluses into negatives and I find that horizontal cylinders just don't work very well nor efficiently. Their useable HW capacity isn't anywhere near it's physical capacity, recovery times are impacted and the few that I've ever had to look at over the time I've worked with UV, seem to be plagued with flow and pressure/expansion issues. Hence my reasoning behind using smaller high recovery PDWH cylinders or smaller fast recover tandem units.

 

[dilalio]

Massive thermocline.

 

[Elsa TLC]

It is rare I disagree with other pros on here but unfortunately in this case I cant agree - horizontal cylinders - OV or UV - are a complete waste of time and money IMO and are really the last resort when it comes to HW storage.

The reason for that is, a HW cylinder's fundamental design is to heat at the bottom section and then convection heats the water above and so on till it heats the whole cylinder hence it's design as a vertical cylinder. It then creates stratification layers stopping the cold inlet from mixing and cooling down the heated water altogether a pretty efficient design.

Turning the efficient vertical cylinder design on its side completely changes those design pluses into negatives and I find that horizontal cylinders just don't work very well nor efficiently. Their useable HW capacity isn't anywhere near it's physical capacity, recovery times are impacted and the few that I've ever had to look at over the time I've worked with UV, seem to be plagued with flow and pressure/expansion issues. Hence my reasoning behind using smaller high recovery PDWH cylinders or smaller fast recover tandem units.

I have fitted a couple with no problems but would argue against your findings.