# Can Unvented Cylinder improve mains flow rate on 2 simultaneous showers?

#### sundarbuild

Hi I have pressure of 1.5bar about 14L/min flow rate with 2 thermostatic showers and so was thinking Ill get a a combi that heats about 14L/min. Worst case is Ill get 2 showers 7L/min which is okayish.

However someone suggested unvented cylinder if 2 showers but how will this give me more L/min as don't you just get out what you get in.

Was looking at the helpful ladies at heatinghub and suggests if pressure is good and multiple showers on simultaneously then use unvented, and they don't consider flow rate.

So if unvented would I get 14L/min out of both thermostatic showers?

I have had an unvented before briefly in a rental house and I recall the shower flow/pressure dropping off lots if someone had another shower hence my working assumption you just get out what you get in even with unvented

If your flow rate is 14 lpm then that is all you will get .

Thanks Terry. So if 2 showers running simultaneously that would be 7L/min each

So if 2 showers running simultaneously that would be 7L/min each
Theoretically yes.
In reality it could end up as some other split such as 10 and 4.
In any case, there is no way to get more flow that the supply can provide without installing storage / pumps / accumulators.

Hi I have pressure of 1.5bar about 14L/min flow rate with 2 thermostatic showers and so was thinking Ill get a a combi that heats about 14L/min
Unless you actually want 14l/min at the output temperature of the combi (which is far too hot to shower in), then that's not worthwhile either - a shower will mix a significant amount of cold water in as well. 14l/min is the total of both hot and cold, so if your shower used 65% hot and 35% cold, you would only need about 9 litres/minute of hot water to do both showers, the other 5 would be cold water.

1.5 bar @14L/Min would be below the threshold for installing an un-vented cylinder IMO.

Is that reading dynamic too? More than one outlet fully open at the same time?

Most combi outputs of HW are nominal and set at a 35deg rise, if your winter water is below 5deg ....

Very rarely you will get the max as rated in their MI specs, also keep in mind that they use the same cold water as the showers and other outlets do, so again it comes down to the dynamic mains supply.

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