Complex central heating system

[nazza]

I would be grateful for the collective advice of heating engineers.

I live in a large detached property which is over 3 levels and has 5 bathrooms in total. Each floor has 11 radiators each and the central heating and hot water is supplied by a combi boiler on each floor ( 3 combi's in total) I am looking to change the central heating system to a "proper system" and install a system boiler with an unvented cylinder. Each level would have its own zone valve and controls so the central heating can be independently controlled.

I have had a few engineers come out to have a look and they have recommended 2 system boilers connected together with a 300L water cylinder. I have been recommended the following options: 2x Worcester Bosch 35kW, 2x Vaillant 37kW, 2x Atag i40S, 2x ACV prestige solo 42 or 1x ACV heat master 70TC (this has a built in water cylinder)

Water cylinder: Either a standard megaflow 300L or ACV smartline 300L with TMV

In terms of material, this has been specified as:
Low loss head, 1x twin head CH pump, 1x bronze pump, 4x zone valves amongst other things.

I realise this is a big job and from doing some research, it seems apparent that ideally a heating engineer with some experience of fitting commercial heating systems would be beneficial as this is not a straight forward system to fit out. Obviously I want the job to be done correctly so that the system works optimally and lasts for many years to come. There are quite a few options and I am not sure which to go for.

What would your advice be with regards to:

1) Boiler size and recommendations above. Would 2x Bosch or 2x Vaillant be sufficient? Do both boilers switch on at the same time whenever there is a demand for CH or HW or can it be programmed so that only 1 boiler will work if needed?

2) Is there any advantage to the ACV smartline water tank over a conventional system. There is a massive difference in price between the two.

3) I realise that the ACV are commercial boilers. Any pros and cons with fitting them in a domestic property. From what I understand, when these boilers are connected then if the demand for CH or HW is not there then only 1 will switch on?

4) From what I have read, it is essential to have a low loss head installed?

Any other hints and tips would be appreciated.

Look forward to your recommendations. Hope the description above is easily understood!

cheers

 

[muggles]

I have had a few engineers come out to have a look and they have recommended 2 system boilers connected together with a 300L water cylinder

300L is a bit small for 5 bathrooms...

I realise this is a big job and from doing some research, it seems apparent that ideally a heating engineer with some experience of fitting commercial heating systems would be beneficial as this is not a straight forward system to fit out. Obviously I want the job to be done correctly so that the system works optimally and lasts for many years to come.

How "correctly" are you thinking? In an ideal world you'd take the whole lot out and start from scratch, new pipework, new rads etc etc, but I get the impression you're not looking to do that. Some pipework up from the new boiler location to join up the existing ones could work though, with a zone valve in place of each of the three boilers. Where in the country are you? Might be able to recommend someone...

What would your advice be with regards to:

1) Boiler size and recommendations above. Would 2x Bosch or 2x Vaillant be sufficient? Do both boilers switch on at the same time whenever there is a demand for CH or HW or can it be programmed so that only 1 boiler will work if needed?

No idea whether two would be sufficient, because we've got no information on the heat loss for your property. It might turn out that one is sufficient. You can use a whole house heat loss calculator to find the correct answer to that (requires a bit of maths). A cascade control will sort out whether one or two boilers need to fire at the same time, if two boilers are indeed required.

2) Is there any advantage to the ACV smartline water tank over a conventional system. There is a massive difference in price between the two.

Yes and no. It depends on whether the installer is using a hot water priority setup to heat the water. If they are then the ACV is an option, although in reality the heat recovery time on them isn't too much different to a Joule Cyclone High Gain. The WB CDi can have a diverter kit fitted to achieve this, not sure about the others you've listed. Intergas can also do it without having to buy extra kit from the manufacturer, and will also run the heating on OpenTherm which the WB can't do

3) I realise that the ACV are commercial boilers. Any pros and cons with fitting them in a domestic property. From what I understand, when these boilers are connected then if the demand for CH or HW is not there then only 1 will switch on?

Major disadvantage is that only people with commercial gas qualifications can work on them, which will increase both your installation and your maintenance/servicing costs significantly. Domestic boilers can be sequenced to match demand as well

4) From what I have read, it is essential to have a low loss head installed?

As with the question about whether two boilers are needed, it depends on things we can't see from here, but a LLH might be helpful.

Any other hints and tips would be appreciated.

I've hinted already, but I'd be looking at Joule Cyclone High Gain cylinder(s) and Intergas boilers. As I said before, if you can give us your location (nearest town will do) we might even be able to suggest a suitable installer for you!