Will this boiler be up to the job?

[dedvendies]

Hi there, wondering if I can get some advice?

I've got a house, 5 radiators and one bathroom.

We have a Greenstar 24i Combi Junior, the speed of the hot and cold water is pretty good.

But when you turn a tap on and you're having a shower the pressure of the shower goes down. If you turn on a hot tap the shower goes cold, if you turn on a cold tap the shower gets hotter.

The hot water is 9.5 litres a minute, 24 KW Heat.

We're getting an extension which means one more radiator, wet underfloor heating downstairs and another toilet and shower downstairs.

We're looking at getting a Greenstar 42 CDi Classic (17.2 litres a minute, 30KW heat).

Is this up to the job?

Thanks in advance for any help.

 

[ianmcd]

If you have the space you would be better fitting an unvented HW cylinder and keeping the existing boiler , it will be able to cope with your heating requirements

 

[dedvendies]

Hi there, thanks for the advice.
I might have room downstairs, how large are they, do they need to be near the boiler?
If I didn't get a HW cylinder what might be the problem?

 

[dedvendies]

Oh and do I need some kind of expansion vessel as well?

 

[lightning]

It all depends on pressure and flow you have, combis are sized on hot water not heating.
Any combi you have will have poor performance if you open and other tap washing machine etc

 

[ianmcd]

your combi already has an expansion vessel, and different makes of unvented cylinder deal with their expansion in different ways so will depend on which cylinder you choose

 

[dedvendies]

Great thanks for all the help.

So I was looking at a Greenstore SC-210 which has a hot water capacity of 210 litres, is this over kill for a family of 4?

Is there some kind of formula that is used to estimate what size cylinder to get?

Thanks again.

 

[AGAS]

You don't have to use Worcester cylinders their are better and cheaper ones available

 

[Doggit]

As Lightning has suggested, you need to get the flow and pressure of the cold water checked out first, as you may need to upgrade the water pipe to the property as well. Iams suggestion of fitting an unvented HW cylinder is a reasonable one, but if you don't have an adequate flow and pressure, then you'll still get the same issues, so factor in an upgrade as well.

The drawback of an unvented cylinder, is that it needs to be serviced every year by law, whereas if you don't service your boiler, no one's going to worry.

We can't advise you on the Greenstar being up to the job, as we have no idea of you're setup, but it's an obvious improvement on the current boiler, but it could be overkill. On the other hand, if you're going to run 2 showers at the same time, then you haven't doubled the 9.5 flow rate, and you'd still get an issue if you turned on a hot tap, but a 32mm incoming mains would stop the pressure drop if a cold tap is turned on.

Do you have the budget to replace both boiler and unvented cylinder, as I was reading a post recently that recommended an intergas boiler, linked with a 170l cylinder, and that gave a quick reheat time, so saved on needing a larger boiler.

One of the experts will be along later.

 

[dedvendies]

Hello again.

Thanks for all the help so far.

So I turned on the outside tap which is right outside the kitchen, no other taps were on and a 12 litre bucket filled in 53 seconds so, does that mean I have a 13.58 litres a minute flow rate? Is that good?

So how do you go about calculating what you'd need to have two showers going at once?

We're getting an extension to the back of the house, so that means the old bathroom and kitchen is going, so I'm trying to figure out what we need really. If I need to get a new combi boiler and a HW cylinder then I'll find the budget

I think the mains water comes into the house from the front, so I'm not sure what size the pipe is coming into the house.

 

[flameport]

does that mean I have a 13.58 litres a minute flow rate? Is that good?

That is the flow rate, and no, it's pretty poor.

As far as 2 showers or 2 of anything else, the theoretical maximum flow for each would be half, so about 7 litres per minute.
Whether you consider a 7 l/m shower to be 'good' is a matter of opinion.

 

[dilalio]

The next step is to look into the mains supply into your property. Get the water board out to measure the pressure and (more importantly) flow at their connection to your property. If it proves to be much better than you get at your (unrestricted) outside tap, then you need to consider the feed you have inside your boundary and whether it needs upgrading to, say, 25-32mm mdpe.
If the supplier’s pressure and flow is also poor at the Street connection, then you can venture into the realm of accumulators and pump sets to boost what the board are giving you.
You really want 16+lpm.

 

[ianmcd]

just understand that even if you decided to go for a large combi you still need the same flow rate requirements

 

[muggles]

We're looking at getting a Greenstar 42 CDi Classic (17.2 litres a minute, 30KW heat).

Is this up to the job?

It'll give you all the hot water your mains can provide, but it'll be terribly inefficient on your small heating system as its minimum output is likely to be very close to your system's maximum. If you can get over your Worcester fixation, you'll find there are much better products on the market, usually for less money

As above, you'd be best off finding out whether it's possible to upgrade your mains supply before doing anything else. If 14l/min really is the best you can get, you may as well have a combi and accept that you can't run two showers simultaneously.

 

[dedvendies]

Ha ha, sorry I'm not fixated on Worcester, I have 0 plumbing knowledge so I'm just going for this as my current one is a Worcester.

Basically I'm getting an extension, never done the process before.
I've got planning permission done and going through the building regs stage and I'm just unsure of when the plumbing decisions should be made and the company we're going with isn't really guiding us through the project.

I'm guessing the more detail we have decided then when we put the job out to tender we'll get more accurate quotes as everything has been considered and decided upon.

So should I seek out a plumber, a consultant plumber, sorry I'm new to this!