Domestic Hot Water calculations

[LaytonSteadman]

Hi there!

I have decided to replace my boiler - I have a 2-bed 1-bath flat.

It seems that most Combi boilers have roughly the same CH output - say 24kW. The point being they are more than what most people need:- 7 rads in my flat. So it depends on the hot water required.

I have cold water mains input measured at 25 l/min at the cold tap (10 litre bucket filled in 24 seconds) and the pressure is above 4 bar when the pressure regulating value is opened.

So, in choosing a boiler based on the best shower experience possible, I have come up with the following calculations - do they seem to make sense please?!

Cold water input temp - say 10 degrees
Target showering temp - say 40 degrees

Say a 35kW boiler produces 14.3 litres / min with a 35 degree rise.

So, at the shower head / thermostatic valve:

Hot water - 14.3 l/min @ 45 degrees
Cold water - 2.4 l/min @ 10 degrees
Mixed water - 16.7 l/min @ 40 degrees

16.7l/min is a respectable shower flow rate isn't it?

Thanks!

 

[Madrab]

Yes, in the simplest terms.

You also have to add the shower itself and the hose/head into the mix as to what the max flow will be.

Most combi's coupled with a good quality thermo mixer shower and 3/5 position head, with your mains, will give you a more than acceptable shower.

It all starts to get a bit more complicated when you start to add high capacity rain shower heads and multiple body jets etc.

 

[JohnD]

I've got a drencher head and don't like it. Maybe if I had a wetroom instead of an ordinary glass cube it would be more use. Water falling straight down on my head isn't as good as a diagonal spray.

 

[LaytonSteadman]

Thank you - and agree - will keep to a single shower head. But again these seem to vary greatly!

I've got a drencher head and don't like it. Maybe if I had a wetroom instead of an ordinary glass cube it would be more use. Water falling straight down on my head isn't as good as a diagonal spray.

I guess it's a matter of preference. There's a company in America which has what they claim to be an authentic rain showerhead which seems to make drops of water from a trough built into the shower head and they fall with gravity as opposed to squirting jets / spray.