Which boiler...?

[StockwellSteve]

Would be grateful for any advice on the below.

I've got a 3-storey property with two bathrooms and an electric cooker. At some future point (10yrs+) I may add another bathroom.

I'm currently torn between the Worcester Greenstar 37cdi and the 42cdi model. Worcestor claim that only the 42cdi will allow two showers to be run at the same time, but I'm not convinced personally and there's quite a big price difference between the two types of boiler.

Can anyone advise on which I should go for ?

Thanks.

 

[Boilerman2]

System Boiler and Unvented Hot Water cylinder would be a safer bet!!

 

[D_Hailsham]

I've got a 3-storey property with two bathrooms and an electric cooker. At some future point (10yrs+) I may add another bathroom.

I wouldn't take the possibility of an additional bathroom into account at the moment as your new boiler may not last 10 years.

That's progress for you.

However if you decide to take it into account, then a combi boiler will never be able to supply three baths/showers at the same time. Unless, of course, you have an incoming flow rate of about 30 litres/min and install a 75kW boiler!

I'm currently torn between the Worcester Greenstar 37cdi and the 42cdi model. Worcester claim that only the 42cdi will allow two showers to be run at the same time

Which boiler do you have at the moment?

The overriding factor when considering combi boilers is the cold water flow rate into the house. If it's less than 20 litres per minute, you will not be able to run two showers satisfactorily at the same time.

You can measure the flow rate using a marked bucket and a watch at the kitchen cold tap. If you have a garden tap, turn it full on while measuring the flow rate.

 

[bengasman]

I've got a 3-storey property with two bathrooms and an electric cooker. At some future point (10yrs+) I may add another bathroom.

I wouldn't take the possibility of an additional bathroom into account at the moment as your new boiler may not last 10 years.

Another bit of wonderful advice from who has never in his life been a plumber

Two choices, two pro's, two con's.
Take the smaller model and safe £200 now, but if you regret it later on, it will cost you 10 times that to change.
Take the bigger model, pay £200 extra now, and you will always be able to enjoy the extra performance
In case of doubt, go for the bigger model
And don't let our resident arm chair specialist get you worried about life expectancy of boilers. No reason why a good boiler that is properly installed and serviced couldn't last 20 years.

 

[kevindgas]

not a big user of worcesters these days but from the point of view on usage from my customers/my experience (we fit Vaillant 31 and 37kw combi's) the 37 kw boilers will run 2 showers reasonably well but if you add another bathroom i think it will struggle.
with 3 bathrooms i wouldn't be advising a combi as it is very unlikely to be suitable.

 

[Agile]

The overriding factor when considering combi boilers is the cold water flow rate into the house. If it's less than 20 litres per minute, you will not be able to run two showers satisfactorily at the same time.

You can measure the flow rate using a marked bucket and a watch at the kitchen cold tap. If you have a garden tap, turn it full on while measuring the flow rate.

The only flow rate that is important is the dynamic flow rate!

The open pipe flow rate measurement described above and done at ground level will become pretty poor when its gone through a combi boiler and up to the top floor!

Tony Glazier

 

[D_Hailsham]

The only flow rate that is important is the dynamic flow rate!

You can't have a static flow rate! How do you define a "dynamic" flow rate?

Or are you muddling it up with dynamic pressure?

The open pipe flow rate measurement described above and done at ground level will become pretty poor when its gone through a combi boiler and up to the top floor!

But there's no way of measuring that before the boiler has been installed!

 

[Agile]

I dont normally muddle anything up.

I am sure you can find many descriptions of dynamic flow rate.

Tony

 

[D_Hailsham]

I am sure you can find many descriptions of dynamic flow rate.

But flow is always dynamic; you cannot have a static flow.

So, for the second time, what do you mean by a dynamic flow rate?

 

[ianniann]

The only flow rate that is important is the dynamic flow rate!

The open pipe flow rate measurement described above and done at ground level will become pretty poor when its gone through a combi boiler and up to the top floor!

So a dynamic flow rate is a static flow rate, but measured upstairs? ?

You have somehow confused a dynamic pressure measurement, which is actually useful in this context, with a dynamic flow rate which is something else entirely and not relevant here. A dynamic pressure measurement is one taken when the water is actually flowing (ideally at a specified rate, but on/off is a good start when we're talking about mains water), as opposed to just sitting in a pipe. Not to be confused with "dynamic pressure" which is the physical property where a pressure is exerted by a fluid simply because it is moving (eg. aerodynamic lift).

 

[mysteryman]

Come on, guys, stick to the point. No-one invoked a static flowrate, and it is the dynamic flowrate which matters.

True, no domestic combis will feed three bathrooms simultaneously, but that MAY not be a realistic requirement in a three bathroom house. You'll be able to run two showers at once from, say, a 35kW combi, and then a bath immediately afterwards - if the cold main has the dynamic flowrate to supply all simultaneous demands from all taps - hot and cold.

This site should be of help to the punters, but snide comments and smart arses just spoil it for everybody.

 

[D_Hailsham]

This site should be of help to the punters.

Couldn't agree more.

The problem is that the "experts" use terms which the average punter does not understand. So when someone says it's the "dynamic flow rate" which is important, a glazed look will come over the punter and he will mutter, "What's he talking about?"

It's no good suggesting a search on the internet as all you will get is a lot of links to measuring the dynamic flow rate of fuel injectors and of heart valves! There does not appear to be a recognized definition of "dynamic flow rate" in the context of combi boilers.

I suspect that what is meant by the term "dynamic flow rate" is the flow rate when the pressure is a certain value, but that is not defined.

 

[mysteryman]

This refers to the ability of the cold water main to deliver the total required flowrate at sufficient pressure.