2 boilers

Hi,
I'm moving into a bungalow that has a 7 year old back boiler and tank working flawlessley. We will be adding 2 showers, 1 bath, 5 radiators and a towel rail once extension is completed.
To enable staging of the work (we will be living in the house while doing the work) I was thinking of keeping the back boiler and adding a separate combi-boiler.
The question is - what do i run off the combi and what off the existing back boiler?
Philip
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electric showers, heating off combi, water tank off back boiler.
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Jason wrote:

What is the point of installing a combi if it is to be connected to heating only ?
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The storage system is best where you want high flow - filling a bath or a powerful shower. The combi for low flow applications like kitchen sink and bathroom basin, and possibly a shower.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

IMHO the bathroom basin is the very worst application - unless it is very close the delay in the presentation of hot water is really frustrating. Conversely I would put the bath towards the top because the filling takes so long the initial delay is not that relevant and at the end of the process the combi can still deliver piping hot water. Of course I partly damn with faint praise except for the first point.
Jim A
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Of course it depends on where the combi is situated. Same with a storage tank. If you want truly instant hot water everywhere I suppose you'd need a storage tank at every outlet, or a circulating circuit from a storage tank. Can't be done from a combi.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I'm ignoring the electic shower idea - I have just moved from a combi shower to a 9kW electic and it is a pale imitation in my opinion...
so can i get this clear it is suggested to:
a) run the hot water to showers from the back boiler heated tank - i would need to put in pressure balancing tanks for the cold and probably a pump for each shower. It's a mid sized tank apparently.
b) run the hot water to the baths from the back boiler heated tank
c) run the CH from the back boiler heated tank
It seems you all favour the storage tank!
This would be swell (and cheaper probably) - but i hate running out of water, and I'm not sure the old boiler BTU's will be up to the job of 2 bathrooms and 5 extra radiators. Also - we won't be very efficient.
Its still a bit of a dilema - what's the cheapest option?
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Definately not to have two boilers.
Jim A
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It seems too complicated to have two boilers - been there - and unnecessarily expensive for maintenance and potentially difficult to control depending on the systemdesign. Why not aim to switch from the back boiler to a modern new boiler at some time during the work. However, why do you need a new boiler at all - is the back boiler not up uprateable to the new heat output? If you do decide to keep both then you need to think of peak heating load. Would you sacrifice heat output to your radiators to divert it into the hot water? How will you control the system? Could you end up running one boiler just to heat one room some of the time?
If you go for a combi size it for the hot water supply rate that you want which could be more than you need for heating. You could consider a pressurised hot water storage system so that you get mains pressure hot water in your showers without the need for pumps etc. Much beter than a 9kW electric model.
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