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Hi all

I currently have a Combi boiler in my own house and as part of my extension work I'm looking to switch over to an unvented system as there'll be times when I will have two showers running at the same time etc.. I also want to future proof DHW by having the option to add solar for the fuel.. my static pressure is 3.6 bar and my flow rate is 25 litres per minute. I'm looking for decent power on the shower (when only one shower is running at least), and I'd be interested to know at what pressure/flow rate is it wise to start thinking of accumulators/mains boost etc?
 

ShaunCorbs

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do you have space for basically another hot water cylinder?
 

ShaunCorbs

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its on about par for two to be run i would want 300 l as they only work on 50% so 150l so would give you around 15mins for two showers
 

ShaunCorbs

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ShaunCorbs

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What would my performance be like with just the unvented cylinder and boiler?
you would do one shower no problem but you would see the first slow a bit when the second shower is used / kitchen tap etc
 
As Shaun says you should be ok with just an accumulator as already stated your incoming pressure and flow rate is pretty good.
Mains booster pumps are used when incoming pressure is poor, ie less than 1-1.5 bar. Furthermore if the whole street is running a similar set up a mains booster might be affected at peak times, please correct me if I'm wrong Shaun?
As Shaun said accumulators work off the basis of roughly 50% volume is of useful work before it needs to recharge, so as he said a 300lt accumulator will provide 150lt of maximised pressure.
A common misconception is accumulators increase the incoming water pressure, this is not true. They simply maximise your incoming pressure to its capability with outlets flowing.
When systems are designed correctly there is virtually no limit to how many showers etc that can be simultaneously run, of course the greater the amount of outlets running at once the large the accumulator will need to be.
 
Thanks for your help its much appreciated..

My house is not near any others and it's on its own supply so I think I would have been okay if a booster was needed

I think I'll most likely go with an accumulator considering it's not a great expense in the grand scheme of things
 

ShaunCorbs

Staff member
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Plumber
Gas Engineer

Better than the steel ones they tend to last longer
 

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