Unvented central heating system - poor water flow rate (Dab e.sybox pump)

[KristianH]

Hi,

I have recently moved into a property that I plan on renovating. The central heating system is in desperate need of changing and I have someone coming to look this weekend with a view to fitting a new system next week. The house is 280 square metres, 4 bedrooms with 3 bathrooms. It currently has 18 radiators that the system will need to heat. As the renovation progresses the majority of the radiators will be swapped for underfloor heating so the system will have to be able to adapt to the change. There's me, my wife and our 2 children living in the house so ideally we need a system that can cope with 4 back-to-back showers or 2 to 3 showers running simultaneously.

We have been recommended to have an unvented system installed. Unfortunately we have poor cold water mains pressure with a flow rate of 11-12 L per minute. I have done a bit of on-line research and am considering a Dab e.sybox pump with 500 litre e.sytank cold water storage, a Worcester-Bosch Greenstar 35 cdi classic system boiler and 300L greenstore unvented cylinder. Does anyone have any suggestions / recommendations. I've only picked Worcester-Bosch from the Which reviews. Happy for any suggestions. Is a 300L tank unvented tank likely to be large enough? Has anyone had any experience with the Dab e.sybox system or fitted it to an unvented system before? I can buy another tank to increase the cold water capacity to 1000L but this seems excessive.

Thank you for your help / input. I want to have a good idea of what is available / what I want before the plumbers come.

 

[KristianH]

Hi. If anyone does have any advice on boiler make/output, unvented cylinder make/size or the Dab e.sybox or other method/system to increase the flow/pressure for an unvented system please let me know.

Thank you
Kristian

 

[bernardgreen]

If you suck ( pump ) water out of an unvented cylinder faster than it can be replaced from the mains then a negative pressure will occur inside the cylinder and this could result in the cylinder collapsing inwards.

This is one situation where a vented cylinder gravity fed from a storage tank in the loft may be the better option. Then pump from the cylinder. If there is a risk of the storage tank becoming emptied then a float switch should be fitted so that the pump is stopped before the storage tank is emptied.

Or you could ( maybe ) pump water from the storage tank into an unvented cylinder but that approach would require more complicated controls and safety devices.

 

[KristianH]

Thank you. I think the plan would be for the 500L water storage with pump to be before the unvented cylinder / boiler. From what I have read you can set the pressure for the house at up to 6 Bar and flow rate to over 100L a minute (obviously wouldn't set it to the max settings). This I presume just becomes the new mains pressure (as long as you don't use up the 500L tank). An additional 500L storage tank can be fitted but they are an addition £400 approx and I'm not sure if it would ever be needed.

I called a company that sells / fits them and they advised they fit them for unvented systems so hopefully should work.

 

[KristianH]

At the minute we have a pumped power shower in the bathroom from a gravity fed system. Can this be used still if we swapped to an unvented system? The motor/pump is housed behind a stud tiled wall!

 

[Roger928]

At the minute we have a pumped power shower in the bathroom from a gravity fed system.

Stick with that system.
If you change to unvented it becomes fully pumped and you have a pump kicking on and off all the time and giving a lot of trouble and the installation expense will be well into 4 figures. Not worth it imo.

I have two gravity systems in my home operating all the showers.
No pumps needed. Granted the ground floor one works the best.

My mains pressure is more than ample to run an unvented but not worth the hassle of having such a risky contraption. (Never mind start pumping it)
Even the last plumber I had agreed.
And he is G3 qualified.

 

[bernardgreen]

My mains pressure is more than ample to run an unvented but not worth the hassle of having such a risky contraption.

Totally agree with that,