Combi Boilers in Tandem?

[rozzer156]

Hi All

I've got a question which I'm hoping someone can answer -

So I've got a Victorian semi, the previous owner had two Vaillant combi boilers installed, one supplies hot water to the ground floor, one to the first floor - heating the same way (why they went for two and not one large one I do not know).

My question is with regards to the hot water supply. Is it possible to combine the hot water outputs of the two boilers, supplying the whole house from the pair rather than each floor individually? Would this give a better hot water flow rate or ultimately just consume more gas (with no real increase in flow)? Water pressure is relatively high, at the moment the hot water flow rate is nowhere near the cold water rate. Shower flow is fine, just takes ages to fill the bath.

Cheers

 

[Bahco]

I suppose that if both boiler hot supplies were connected to one tap, then both would fire when you opened the hot tap.

Sounds dangerous to me though. See what the Corgis think of your idea.

 

[D_Hailsham]

Are you sure the previous owner installed the boilers? The boilers might have been installed by an earlier owner and the house could have been divided into two flats, so a boiler for each flat.

 

[rozzer156]

Good point, but I've got a copy of the original installers installation plan somewhere. My thought was that it was originally spec'd with two boilers due to the number of radiators - but I may be wrong. Both boilers are fed by a single gas meter, so to me that would rule out previous usage as flats - I think the boilers were the first central heating that the house had - they survived for a long time on a mix of solid fuel and gas fires prior to that!

 

[BingoBongo]

you can easily get 1 boiler to supply the rads (give ammount and sizes)
its more likely the 2 combis were for the number of hot water draw offs. (how many baths/sinks ?)

 

[bengasman]

Why on earth would you want to do that?

 

[BingoBongo]

i didnt

ive seen it done in large houses where 1 boiler supplies 1 half,just like spliting the building in 2.

 

[rozzer156]

BingoBongo in response to your point about hot water draw off's - there's quite a few. 3 showers, 1 bath, adding the sinks up comes to 8 (that figure surprised me, but that includes ensuites, kitchen, utility, etc). Having said that we don't have all the sinks running at the same time!

Radiators amount to 12 on the ground floor and 9 on the first floor. They vary in size from 600 x 600 singles to 1500 x 600 doubles (some rooms have two rads). My neighbour has got a single condensing boiler supplying his whole house so certainly doing this with fewer boilers is possible. My though in the longer term is we'd be better off with a more modern condensing boiler and an indirect hot water cylinder or something like that.

However this still goes back to my original question - the biggest issue is the speed at which the bath fills, that's why I raised the initial question about the possibility of combining the hot water outputs of the two combi's.

 

[Agile]

It is possible to combine then but that needs additional pipework from boiler to bath to be done to best effect.

You would be better off with an unvented cylinder and condensing boiler.

Tony

 

[Norcon]

It is possible to combine then but that needs additional pipework from boiler to bath to be done to best effect.

You would be better off with an unvented cylinder and condensing boiler.

Tony

http://www.screwfix.com/talk/thread.jspa?forumID=25&threadID=27625&messageID=269472#269472

Are you forgetting what watersystems taught you Agile?
Are you suggesting fitting a UV cylinder will require less pipework than combining the outlets on 2 combi's for the bath?
Also if his supply to the bath is too small for a twin combi flowrate then its certainly going to be too small for the UV cylinder assuming his mains is up to it.
Can you give a valid reason (he won't ) why the OP should spend about 3 grand using your option when he probably only needs a pipework modification costing less than 1 grand?

 

[rozzer156]

Norcon - thanks for the link, makes an interesting read. So it sounds like it's possible but there's more to it than simply combing the two outlets, though it doesn't sound too complicated. My tripping point maybe that we've only got 15mm to the bath - it sounds like from that thread it would need to be a dedicated 22mm feed to get the full benefit. The comments are interesting about the zoned CH, that's the way ours is set up and it works a treat - we can have upstairs coming on at completely different times and set the temperature differently. The boilers take up a fair amount of space in the utility but I guess no more than one boiler and a cylinder would.