Combi boiler and mixer shower

[SebH]

Hi

I'd like a mixer shower with large head in my new loft bathroom but have been told there will not be enough flow from my combi boiler, which is housed in my cellar. The boiler is a Baxi-potterton 30kw, with a nominal flow of 12litres/min for 35ºC rise in temp. (The cold water is mains fed with no tank).

Options I have considered but am not sure will work are:
1)Replacing the boiler with one having a sufficiently higher flow rate?
2) Getting an electric shower, but would like the unit to be concealed?

Has anyone any suggestions?

Thanks

Seb

 

[ianniann]

Who told you there wouldn't be enough flow?

The flow rate will be determined first by your mains pressure. You can test this yourself. Ideally test it through a shower head in the attic since the pressure may be slightly lower than the ground floor. Test hot and cold separately, then both together. Or you can test it through a tap which will give you an idea of potentially how much water is available.

Secondly the usable flow rate will be limited by the power of the boiler. It can heat 12l/min by 35C which is a pretty good shower, but if you want 15l/min then your boiler wouldn't be able to heat it enough except perhaps when the incoming water was quite warm in summer.

An electric shower will never come close to even the poorest combi boiler on lower than average mains pressure, and it will be expensive to run.

 

[SebH]

Thanks ianniann

It was the company who are doing my loft conversion who informed me. They said that the flow would be weak from a large fixed shower head because of the vertical distance between the boiler (cellar) and the shower head. But a smaller head on a hose would be OK.
I wanted a large fixed shower head so I could avoid having a traditional hose, to keep things looking neat.

Thanks for the advice, so electric is ruled out. I'll try checking the flow rate I get in the attic with a hose pipe (15mm bore) attached to first floor bathroom taps to replicate the pressure I'll get when its all plumbed up.

Then I can check on the shower head specifications to see what flow is recommended, and see if there are any fixed heads that fit my bill.

 

[ianniann]

The attic guys may have tested your water pressure. Or not! Minimum supply is supposed to be 1bar, but is occasionally less in older properties or out in the middle of nowhere. Sometimes a lot more. 1 bar will get the water to the attic but not a lot left over to push it through the shower. The more typical 3-4bar will feed any shower you can imagine and then it's just a case of what the boiler can do. If you have a combi boiler than you almost certainly have a good bit more than 1bar.

Don't panic immediately if the hose doesn't work too well. The plumbing to the attic should be done with a larger, and hopefully straighter, pipe than your hose. Remember that the flow rate and the pressure are two different things and not always closely related. Flow rate through a shower is actually quite low compared to say a wide open tap, but the shower head needs a fair amount of pressure to work properly.

 

[SebH]

Thanks again

I'll try and get this done over the next week.