combi boilers

[mfgs]

Does anyone know of a combi boiler which has a 40kw output for central heating?

 

[SimonJohns]

Strebel/ atag I think do one

 

[ambrosia]

wow, thats massive, whats the installation, vaillants biggest combi the 937 (which is a big lump of a boiler to install) only has a max of 28kw on the heating side

 

[ecowarm]

That's a big property for a combi

 

[mfgs]

I know its big and I have advised against it, but they want one and are getting quotes from others for having a combi and I dont want to miss out on work by refusing to fit one for them if they are dead set on having one. I am just trying to find the best option for them. I normally fit Worcesters but their biggest combi's only have 30kw on the heating and that just wont be enough.

 

[Hardy1]

that is a big property for a combi how many rads ? and roughly whats the sizes?

 

[Roger Welton]

What about two smaller combis, one for upstairs heating and water one for downstairs, or a combi and system boiler linked together. Depending on what else you find the large atag is quite pricey so maybe cheaper.

 

[mfgs]

I cant actually find a price for the 51kw atag. I have never had to link boilers together before so wouldnt know what special requirements in terms of pipework would be needed?

 

[ggman]

This could be the boiler for you. Very strong and efficient suitable to any system.

[DLMURL]http://www.mcncaldaie.com/BLUCOND.pdf[/DLMURL]

 

[Roger Welton]

I like using a low loss header, to give decent hydraulic separation between boilers and system.

All I can see price wise for the atag online is for the system version and that's just shy of £3k

[DLMURL]http://www.google.co.uk/m/products/catalog?hl=en&safe=off&client=safari&biw=320&bih=416&q=atag+boiler+q51&um=1&ie=UTF-8&tbm=shop&cid=1183012865525120520&near=Axminster,%20UK&sa=X&ei=fv-vT9j5JcS_8wPhgqGPCQ&ved=0CDcQ8wIwAA[/DLMURL]

 

[mfgs]

Yeah I found the system boiler. I dread to think the price of the combi if the system boiler is near enough 3k.

 

[Roger Welton]

I suppose they can charge what they like when they're the only company making a boiler in a particular niche

 

[ambrosia]

how about cascading boilers, you could put 2 greenstars next to each other then
although i have no idea if you can do it with combi boilers but i dont see why not, it certainly can be done with system boilers, pipework will be the same except for a non return valve on flow, then you have 1st boiler operating at 30% and the next at 90% lag and lead

http://www.worcester-bosch.co.uk/installer/literature/technical-bulletins?category=all&page=4

 

[AWheating]

do you know what boilers have been quoted by others??

it must be alot of radiators to need 40kw. 30 room house with one bathroom? lol.

 

[Roger Welton]

how about cascading boilers, you could put 2 greenstars next to each other then
although i have no idea if you can do it with combi boilers but i dont see why not, it certainly can be done with system boilers, pipework will be the same except for a non return valve on flow, then you have 1st boiler operating at 30% and the next at 90% lag and lead

Technical Bulletins - Worcester, Bosch Group UK installer site

That would work with a combi and a system boiler, and is what I would probably do myself in this situation, however it's not strictly a cascade system.

As I understand it a cascade controller will load up boilers sequentially, so boiler one will modulate up to full output before boiler two cuts in and loads up, and so on. The benefit being you get a much better turn down rate than with a single larger boiler.

And as has been said a few times, a combi as the only hot water supply to such a large property seems to make no sense unless there hot water demands are incredibly low.

 

[mfgs]

Not sure what other boilers. Just mentioned 40kw combi's. There are 22 radiators currently, some of which may need to be made bigger as rooms arent hot enough and also there may be an extension with another couple rads needed in future. There is one main bathroom and 1 ensuite. 30kw for the heating will be borderline.

 

[jtsplumbing]

This sounds to much for a combi ! what length pipe runs for the hot water ? may have to think about cylinder with secondary return.

 

[mfgs]

This sounds to much for a combi ! what length pipe runs for the hot water ? may have to think about cylinder with secondary return.

That would be ideal, but not what the customer wants. I have suggested it.

 

[galaxy_plumbing]

Why they don't listen to experienced engineer? Its like going to restaurant and tell chef how to cook.

 

[mfgs]

Probably because other firms have already been there and quoted for combi's. Not one of them had mentioned unvented cylinders, so I am in the minority here with my viewpoint. Although all the other companys were big firms I think and the people that do the quotes are likely to be just salesmen with no experience in the trade.

 

[Phoenix Heating]

Put check valve on mains going into boiler, then tee of after it then put in secondary return from furthest point that taps back to incoming main after the check valve, with pump remember you will need another check valve as hot returns to cold, it just circulates around boiler flow switch and modulates, use pipe stat at far end to controll pump and stop unecaserryly surculation.

 

[Phoenix Heating]

Viessmann are bringing out a 35kw heating and 35kw water combi.

 

[jtsplumbing]

Seems that customer only wants a Combi ! Fine they know all about it, just fit what they want ! get them to sign paper work on the understanding that if it dos not work its down to them, they have gone against what was recomended. after all the customer is always right ! LOL :dunce:

 

[grahamgas]

The discount price for installers for the Atag Q51 combi is £2369 plus the flue and vat.
Personally if they are that hell bent on a combi, then I would would.
sometimes you have to know when the job and the customer are going to be a nightmare.

If they do want to listen to common sense, then I would go unvented for the water and maybe two system boilers cascaded for heating load, with llh.
Obviously have to watch that meter capacity if it is a standard u6/g4

Graham

 

[smhstu]

How about a worcester gb162 with a unvented cylinder?