Suitable electric hot water system

Withywonderer

Hi, I am considering replacing an old vented hot water cylinder with a huge tank on top of it which is suppling a kitchen mixer tap 7 m away and 2x basin mixer taps in an all electric 2 bed apartment. The maximum hot water pressure to the kitchen mixer tap is ridiculously low at just over 2 lit/min and by the time the water travels 7 m at low pressure it has lost some of its heat. The shower is separate on a different circuit. I need advice and cons and pros as to what is the most convenient system to choose which will give adequate pressure for the 3 mixer taps. 
I have in mind either of the following:
1. Instant hot water similar to Stiebel Eltron DCE- X. Operating at 14 kw, what kind of cabling and circuit breaker would I need? Would a typical 2 bed apartment power supply be able to accept such a power hungry beast? Has anyone installed or using one and happy with the pressure?

2. A 90 or 120 litre unvented cylinder similar to Telford Hurricane. Operating at 6KW would I need to change the cabling which is already there for the 3 kw immersion heater? 

Any advice regarding above 2 or any other system will be really appreciated.

Withywonderer

Withywonderer needs advice

Rdwill

What you need is one of these. Google hot water pump and save yourself a few thosand.

https://www.fountain-filters.co.uk/Hot-Water-Booster-Pump/0-CAAA010/PRAA125.htm

nofoollikeold

1. Provided your cold water storage cistern ((CWSC) tank above hot water tank) is big enough the Rdwill's suggestion is probably the most cost efficient.  Must be installed to manufacturer's instructions and you would probably need a "universal" or "whole house" type.  
2. The Stiebel Eltron at 14 kW would draw around 56 amps.  I'd be concerned that such a load, coupled with a possible cooker and / or washing machine on at the same time would likely exceed the installation capacity, which is likely to be around 80 amps.  It would also need a cable of around 20mm cross sectional area, which is way more than normal domestic cable.  
3, An unvented cylinder would be the most elegant solution, giving you mains pressure hot and cold, and eliminating the CWSC.  However, be aware that:
3.1 The incoming cold water mains pressure must be a minimum of 2.0 bar measured with at least one mains connected outlet running. (Dynamic pressure).  Requires a pressure gauge to measure.  
3.2 The incoming cold flow rate needs to be at least 20 litres per minute.  Measured "open pipe", i.e. with no restrictions between the incoming water and the outlet used for measurement.  Can be measured with a bucket and stop watch.  
3.3 If it has two immersion heaters (one to heat whole cylinder, the other to heat top third of cylinder), each with require a 3 kW supply.  You cannot use an existing 3 kW supply to source a 6kW load.
3.4 It will require a pressure relief pipe set.  Generally this must terminate outside the property an be in copper.  There are some exceptions where particular high temperature resistant plastic pipe can be used.  You'd need a site survey to determine.  

Ectophile

Withywonderer said:

Hi, I am considering replacing an old vented hot water cylinder with a huge tank on top of it which is suppling a kitchen mixer tap 7 m away and 2x basin mixer taps in an all electric 2 bed apartment. The maximum hot water pressure to the kitchen mixer tap is ridiculously low at just over 2 lit/min and by the time the water travels 7 m at low pressure it has lost some of its heat. The shower is separate on a different circuit. I need advice and cons and pros as to what is the most convenient system to choose which will give adequate pressure for the 3 mixer taps. 
I have in mind either of the following:
1. Instant hot water similar to Stiebel Eltron DCE- X. Operating at 14 kw, what kind of cabling and circuit breaker would I need? Would a typical 2 bed apartment power supply be able to accept such a power hungry beast? Has anyone installed or using one and happy with the pressure?

2. A 90 or 120 litre unvented cylinder similar to Telford Hurricane. Operating at 6KW would I need to change the cabling which is already there for the 3 kw immersion heater? 

Any advice regarding above 2 or any other system will be really appreciated.

1. That's a monster boiler, requiring around 58 to 60A.  Your main fuse is probably between 60A and 100A.

2. Probably not, unless someone used over-sized wiring when it was installed.  6kW is around 26A.

Is there any reason a normal 3kW immersion wouldn't do?

FreeBear

Withywonderer said: Any advice regarding above 2 or any other system will be really appreciated.

Have you considered a thermal store such as a Sunamp ?

They typically have a <3kW heating element and can provide instant hot water at mains pressure. That would save on any costly electrical upgrades, and only need minimal changes to the plumbing. You'd still have a delay getting hot water in the kitchen.

The alternative is under counter water heaters with say a 5l storage tank - This could work out to be quite a bit cheaper than a Sunamp or unvented tank at £100-150 each (plus installation).

Albermarle

nofoollikeold said:

1. Provided your cold water storage cistern ((CWSC) tank above hot water tank) is big enough the Rdwill's suggestion is probably the most cost efficient.  Must be installed to manufacturer's instructions and you would probably need a "universal" or "whole house" type.  
2. The Stiebel Eltron at 14 kW would draw around 56 amps.  I'd be concerned that such a load, coupled with a possible cooker and / or washing machine on at the same time would likely exceed the installation capacity, which is likely to be around 80 amps.  It would also need a cable of around 20mm cross sectional area, which is way more than normal domestic cable.  
3, An unvented cylinder would be the most elegant solution, giving you mains pressure hot and cold, and eliminating the CWSC.  However, be aware that:
3.1 The incoming cold water mains pressure must be a minimum of 2.0 bar measured with at least one mains connected outlet running. (Dynamic pressure).  Requires a pressure gauge to measure.  
3.2 The incoming cold flow rate needs to be at least 20 litres per minute.  Measured "open pipe", i.e. with no restrictions between the incoming water and the outlet used for measurement.  Can be measured with a bucket and stop watch.  
3.3 If it has two immersion heaters (one to heat whole cylinder, the other to heat top third of cylinder), each with require a 3 kW supply.  You cannot use an existing 3 kW supply to source a 6kW load.
3.4 It will require a pressure relief pipe set.  Generally this must terminate outside the property an be in copper.  There are some exceptions where particular high temperature resistant plastic pipe can be used.  You'd need a site survey to determine.  

Regarding the comments in bold.
I know that for an unvented system, you need some minimum pressure and flow rates for it to work to its full potential ( such as being able to supply hot water at decent pressure to more than one outlet at once).
However I would not have thought a pressure below 2 ,or a flow rate below 20, would actually make the system completely unviable ?