water flow rate for new boiler

[terry345]

Hello,
we was told by an engineer our water flow rate was 10 litres per minute. I just wanted
to know whether or not it makes a difference to the cost of running the boiler or any other
difference if a new boiler was installed with a higher flow rate than this e.g we were
recommended the worcester bosch 25si compact, with a Domestic hot water flow rate: 10.2 litres per minute.
I was reading online that the worcester bosch 28CDi Compact has a Domestic hot water flow rate: 11.4 litres per minute.
Would this be detrimental or have a negative effect. Unfortunately the quote was too high for us anyway, but I was just
wondering as the engineer seemed to not want to give a quote on the 28cdi (which is supposed to be a newer, top of the range version), and said it was primarily because the flow rate was higher than the 10.
Any contributions or thoughts welcome. Cheers.

 

[Mike Jackson]

With a flow rate of 10 l/min I would not be recommending a combi boiler. An entry level boiler wants 9 l/min incoming to function correctly, you may have enough flow for that but your incoming needs to be divided between hot and cold and with a flow rate of just 10 l/min when you open a cold tap the flow to the boiler will decrease and could present a scalding risk.

As a rule of thumb I like twice the flow rate to the boiler as an incoming flow rate. i.e. if the incoming flow rate is 18 l/min I will recommend a 24 Kw boiler giving 9 to hot and 9 to cold.

 

[Ermintrude]

What he said!

 

[IDCHAPPY]

What they said^^

 

[oz-plumber]

Gee you guys have incredibly low flow rates and even more incredibly low water pressure.

People winge over here when we install 500kPa pressure reducing valves at the water meter - which is standard practice.
Before that requirement most places would have @ 1000 kPa and more.

 

[terry345]

Hi there.

We currently have an old Potterton combi boiler, so was looking to replace it.
Your're right, at the moment, if someone is using the shower (or bath)
in the bathroom and another person turns on the hot water in the kitchen (where the boiler is),
suddenly the hot water flow from the shower tap drops considerably and the water
from the shower is colder...then, when the kitchen hot water tap is turned off,
the water suddenly spurts out hotter from shower tap (or bath), which does present a scalding risk.
In this situation, the worst thing to do is when someone is in the shower and
this happens, is to increase the hot water tap in the shower even more to compensate for the
loss, which has happened many a time, because as soon as the kitchen hot water tap
is turned off, the hot water pressure to the shower increases and it comes out even hotter -
so anyone in the shower normally has to wait for someone to stop using the
kitchen hot water tap or any another hot water tap - and we usually have to listen out.


We live in a 3 bedroom flat with 9 radiators. We're using gas, so what boilers
would be recommended to use instead? Thanks for info so far.