Loft conversion - combi + unvented (Turn off when not needed?)

[wej99]

Hi all. Due to have our loft converted soon and will be adding a new bathroom and shower. We have a combi boiler (WB 32 CDI). Thinking of also having an unvented water cylinder fitted.

The loft bathroom will be used primarily for guests. Is it possible to have the loft bathroom hot water running primarily from the combi, and having the unvented as a secondary, leaving the unvented cylinder turned off and only turning it on when we have guests over (to be able to run showers in the 2 bathrooms at once)? I'm keen to not having it running all of the time when we can rely on the combi for day to day hot water without guests.

Thanks.

 

[dilalio]

Much of this depends on your incoming cold main flow rate and dynamic pressure.

Min of 22mm mains all the way to the UV.

Remember pressure Loss as you get higher and also during peak demand.

Same goes for combi as its main fed, but not the 22mm pipe.

 

[wej99]

Thanks dilalio. We're having the mains pipe replaced into our house next week so I'll take a measurement once done. Thames Water measured at the meter yesterday at 30l/m and 2.5bar but this will hopefully increase once they've changed the lead pipe on their end too.

 

[dilalio]

Thanks dilalio. We're having the mains pipe replaced into our house next week so I'll take a measurement once done. Thames Water measured at the meter yesterday at 30l/m and 2.5bar but this will hopefully increase once they've changed the lead pipe on their end too.

That's good. Supply is very good.
As I said, take that all the way to the cylinder and 22mm up to loft.

So, what you're saying is you want to be able to switch between combi and UV use?

 

[wej99]

Yes, that's right. I think the combi will be sufficient when we don't have guests as we typically wouldn't have two showers running at the same time). There is a chance that either the loft or main bathroom shower could be used separately during normal day to day use.

I dont want to pay to heat up the UV when we don't have guests as it seems a waste if the combi is enough for the 2 of us. When we do have guests I'd like to be able to run two hot showers at the same time.

 

[Harry Bloomfield]

30l/m and 2.5bar but this will hopefully increase once they've changed the lead pipe on their end too.

The static pressure will remain the same.

 

[wej99]

Agreed. If needed could get a pump on mains in basement ?