Will a combi give me enough flow?

[moodygaz]

I've been looking at combi boilers for a 4 bed 2 bath/shower house, to replace an aging vaillant, in particular the advanta 39c, will this give me enough flow for 2 simultaneous showers or do I have to go for a storage combi?. Anyone know what these cost approximatly so I know wheather or not to rule it out. Working pressure at least 1.4 bar and 24ltrs/hr flow on cold main.
cheers

 

[mickyg]

how much flow do you want at your showers?

 

[muggles]

At 24 litres a min (I assume you meant per min and not per hour) you will get a theoretical maximum of 12 litres/min to each shower. Assuming you use roughly the same amount of hot and cold (this really depends on how hot you like the shower) then you'll require 6 litres/min of hot per shower, which leaves you with 4 litres a min spare capacity on the boiler's max output.

This will work well provided you can guarantee that nobody will use a hot tap while both showers are running, the extra 4 litres a min available flow can soon be used up and as this is only theoretically available anyway (if both people like hot showers there will be less spare capacity) it may well be that overall a storage combi, or even a system boiler and unvented hot water cylinder, will suit your needs better.

 

[Agile]

If you have a dynamic flow rate of 24 li/min at a residual pressure of 1.4 Bar then a 60 kW combi would enable you to run two showers together.

However, I doubt you have that flow rate or that you will find a suitable boiler, storage or immediate.

I find Mug's suggestion of a 50-50 split between hot and cold rather unusual !

Assume a supply temp of 5° C and a typical temperature out from the boiler of 40° then the mixed shower temperature would be about 22°C which feels rather cold!

Tony

 

[mickyg]

Assume a supply temp of 5° C

where do you live?? scotland?

 

[bengasman]

It would be handy if you could describe the expected use/demand, as well as an indication of your budget.

 

[moodygaz]

I am just sick of having to turn off washing machine and dishwasher if I want a shower. also my 2 kids are growing up fast and it won't belong till they're wanting to take baths and showers at the same time as mum and dad. So I would like something capable of supplying a shower if something else is being used at the same time. flow is 24ltrs/min whether I have another tap running or not. pressure goes down from 2.5 to 1.5 approx if I run a tap.Cold main size to property is 25mm, I have a 22mm straight from this to the boiler, teed off in 15mm for the cold taps all stopcocks are full bore.

 

[muggles]

Is your 24 ltrs/min measured at your kitchen tap or directly from the stopcock? If it's from the tap and you can maintain 24ltrs/min at the tap with other outlets running then your flow rate may well be higher, only true measurement is from the stopcock

 

[moodygaz]

Its measured straight from the boiler stopcock which comes straight from the rising main in 22mm

 

[bengasman]

Its measured straight from the boiler stopcock which comes straight from the rising main in 22mm

22 mm main will give you more than 24 l/min unless your pressure is extremely poor

 

[muggles]

Its measured straight from the boiler stopcock which comes straight from the rising main in 22mm

22 mm main will give you more than 24 l/min unless your pressure is extremely poor

...which at a dynamic pressure of 1.4 bar, it isn't poor at all

 

[mickyg]

how much room have you got for the boiler? a store combi might be your answer

 

[moodygaz]

about 600mm wide, 800mm deep and from floor up to the ceiling, its single storey so I aim to take the flue up through the roof.

 

[Agile]

Or for less than £1000 you could buy two Vizo boilers. But only one could use the vertical flue!

You will have to devote more space if you want a high performance and cost effective system which would be an unvented!

Tony

 

[moodygaz]

I could put it the other side of the room where space is not a issue....fill yer boots!