Replacement boiler, what DHW flow rate

[cascas]

Hi,

Im looking to fit a replacement combi boiler.

I know it is an emotive subject as to what is best!, usually I use Ferroli or Ideal (cheap as chips, but only in properties that I do not keep long term). to

I need fit this into a house that I will live in, so looking for something a bit better. i.e valliant/viessman/WB (or any other suggestion) At the moment I think that I will need to build the boiler into the new kitchen cupboard, so size is a factor.

What flow rate should I be specifying for my boiler. The boiler will replace a tank system, and supply:

Kitchen Sink
Bathroom Basin
Small Cloakroom Basin
Thermostatic Bar Shower

 

[D_Hailsham]

What flow rate should I be specifying for my boiler.

It's the other way round! What boiler do I specify for my flow rate.

You need to measure this at the kitchen cold tap using a marked bucket and watch. If you have a garden tap straight off the mains, measure the flow there as some kitchen taps will restrict the flow, particularly modern ones.

A flow rate of 10 litres/min is OK for a single shower, but if you intend having more than one hot or cold outlet running at the same time, the greater the flow the better.

Don't forget that all outlets are fed from the same source. So if someone flushes the toilet while you are in the shower, you may notice it. The same goes for washing machines etc.

The flow figures you seen in manufacturers' literature are based on increasing the water temperature by 35C, which is normally enough for a bath or shower. If you put in an oversize boiler it will enable you to heat the water to a higher temperature, but that's self defeating as you will only have to mix it with cold water to bring the temperature down to a usable level.

You need 2.5kW per litre/min.