Unvented Cylinder or Combi Boiler on

[momer79]

We are planning to do the loft conversation and will be adding an extra bathroom in there.

We like to achieve a good water pressure in loft for shower plus like to have two showers running at the same time or one shower and kitchen sink.

Our static water pressure is 2.1 - 2.5 bar and flow rate is b/w 16 - 18 l/m depending on the time of the day.

We have had few plumbers for advise and they all had different view.

Based on water stats and our need, which one would be the best option for us? Unvented Cylinder or Combi or something else ?

Thank You

 

[oldbutnotdead]

Go both. Cylinder for certain with multiple showers to service, use the combi hot water for kitchen sink if it's nearest the boiler. Put the cylinder close to the showers if you can.

 

[Madrab]

Can you check and test the dynamic pressure and flow? Perform the tests with multiple outlets open, 3 or more.

A combi on it's own will rarely satisfy a high flow shower and other outlets at the same time, without other considerations (water saving taps/water saving shower heads/etc) it's just the nature of the beast.

You also need to understand the dynamic pressure to understand what impact there may be to flow and pressure on your rising main @ >5m up to the attic. That's equates to at least half a bar drop before anything else.

 

[momer79]

The dynamic pressure is around 1.4-1.5 bar and the static is around 2.7 bar.

The dynamic flow is around 12l/m and static is at least 18l/m

 

[MeldrewsMate]

I agree with @oldbutnotdead .
Do you have a south facing roof? If so don't fill it with windows, instead fill it with solar panels, and use the free electricity to give you free hot water for at least 6 months of the year via a diverter such as the Solar iBoost or Immersun.
Stick your windows where the sun don't shine.

 

[Mottie]

I agree with @oldbutnotdead .
Do you have a south facing roof? If so don't fill it with windows, instead fill it with solar panels, and use the free electricity to give you free hot water for at least 6 months of the year via a diverter such as the Solar iBoost or Immersun.
Stick your windows where the sun don't shine.

In the summer when the heating is off, the only gas used was for heating the hot water and our gas hob for cooking. Even then, our gas usage averaged around 35p per day. Hardly seems worth getting solar panels to save that amount.

 

[Madrab]

The dynamic pressure is around 1.4-1.5 bar and the static is around 2.7 bar.

The dynamic flow is around 12l/m and static is at least 18l/m

You're in the lower level for unvented. The supply will be able to support an unvented but you will notice a drop in pressure/flow when more than one outlet is opened. A 12L/Min though as long as you are using a standard thermostatic shower then it would be ok, though you wouldn't really be able to support a high flow/high output shower without a noticeable drop.

You want someone that has experience with advanced hot water systems, to set the whole thing from mains to suitable outlets to ensure it's is tuned and maximises what is available.