2 different boilers on CH system replacement quotes

[Tirglas_7]

Hi

Renovating a home we've bought and were having the boiler and CH system replaced (going from microbore 1 pipe system, to 2 pipe system).

Received a few quotes, one quote is using Worcester greenstar 42cdi, the other Worcester 30si.

The boiler will be mounted on the garage wall where there is plenty of space.

The house is now a 3 bed but we will be converting a basement workshop to another guest room.
So will need 11 - 12 radiators. It will have 1 master bathroom, with separate shower & bath, and 1 ensuite with shower only.

If I'm honest, from the quotes and meeting the people we prefer the plumber/gas engineer who quoted us the 30si.

From some googling I've read it is suitable for 8-10 rads, will it be overworked or underperform when having to feed over 10?

Will the 30si be cheaper to run than the 42cdi?

Out of the 2 for my application what is the best bet?

Any other recommendations or advice very welcome

 

[Agile]

I worry that you are concentrating on the wrong aspects.

The power needed for heating depends not on the number or rads but the heat loss of the building. You can calculate that using one of the programs on the internet. Typically 30 kW will easily heat a six bedroom detached house.

But hot water delivery is your potential problem. You don't say, but I expect you are to use a combi boiler. No combi boiler will properly serve more than one outlet at a time!

A 30 kW combi gives about 11 li/min of hot water and a 42 kW about 15 li/min.

A better solution would to have a hot water cylinder. But if you must have a combi then the 42 kW would be the best choice but still not going to run all your hot outlets at the same time.

You also seem to think that your installers can only install what they have suggested. You can ask any of them to fit any boiler.

Tony

 

[Tirglas_7]

Thanks for the reply Tony,

We are set on a combi as we have no other space for a cylinder.

I'll speak to the installer of the 30si, is there another combi you'd recommend that I haven't listed?

Does the higher the kW rating equate to higher costs?

 

[Agile]

You have only listed Worcester boilers!

Many here prefer the Intergas followed by Viessmann and Vaillant.

You pay for the heat you use.

But a 42 kW will run a mediocre shower and a small tap flow at the same time, just!

I hope that you know you will not be able to run two showers at the same time! That's a combi for you.

Don't you have a loft where an unvented cylinder could be fitted?

Tony

 

[Tirglas_7]

The house doesn't have a loft as it has 2 large dormers front and rear that run most of the length of the roof.

I didn't realise combi's couldn't provide enough flow rate for multiple taps/showers running. I assumed the bigger the combi the more it would supply :-/

Are there any other options if u don't have a cylinder?

 

[gasmanstu72]

A lot will depend on your incoming water main, if you have good flow and pressure the 42CDi will give you great hot water and a very good shower too
ive fitted lots of them and personally think they're fantastic boilers.

 

[Aquaheat]

Many here prefer the Intergas followed by Viessmann and Vaillant.

I hear the Ferroli Modena comes highly rated nowadays!

Jon

 

[Tirglas_7]

The water pressure is 6 bar, the water meter is in the garage. There is a regulator on it so Im not sure if it can be increased (or whether that's is advisable).

So everyone is of the same thinking the 30si won't be sufficient? We probably wouldn't be running more than 1 shower at once anyway. Maybe the odd occasion with visiting guests. My kids are young at the moment, I imagine as they get older demand will increase, so I'd rather future proof myself.

Do all the boilers cost similar amounts to run?

 

[gasmanstu72]

no combi boiler will really do two showers simultaneously, although you stand more of a chance with a 42kw one.
theres not going to be much difference in running either model really,

one thing to know is that you will need a larger gas supply from your meter to your boiler (assuming you get the 42kw) in my experience you'll need 28mm pretty much right up the the boiler inlet.

 

[Tirglas_7]

When you say not going to be much in running either model, do you mean cost wise? Or output wise I.e. Both will give similar performance/output?

The gas feed comes into the garage, a couple of meters from where the boiler is going to be situated, so I suppose it's less of a concern having the larger model?

 

[Agile]

Obviously a 42 kW will use more gas than a 30 kW running flat out.

Its not a matter of only wanting to use two showers together occasionally, you just will not get enough flow rate for two showers.

But if you really must have a combi get a 42 kW.

No space to use in the garage for cylinder?

No place outside for a small extension or shed?

 

[Tirglas_7]

Yes there could be room in the garage, Is a cylinder system much better than a combi efficiency wise?

The combi only runs as and when the hot water is required right? Whereas the cylinder system boiler heats the water for period of time usually morning & evening, then the hot waters stored in the cylinder?

I'm thinking a combi will be more cost effective in the long run, as 99‰ of the time we'd only ever run 1 shower at a time. And we'd only heat the water we need each time.

A cylinder system has only been suggested by one installer, they just said each has its benefits.

Many thanks for all the replies, please don't see me as questioning you experience/knowledge, Im just trying to get the most cost effective installation

 

[45yearsagasman]

A One pipe microbore is a new one on me.

 

[endecotp]

Yes there could be room in the garage, Is a cylinder system much better than a combi efficiency wise?

I'm thinking a combi will be more cost effective in the long run, as 99‰ of the time we'd only ever run 1 shower at a time. And we'd only heat the water we need each time.

Modern cylinders are very well insulated, so the hot water that you don't use is still there. So with both combis and cylinders you "only heat the water you need".

Regarding efficiency, note that running a large boiler at well below its maximum output - which is what you'd be doing while a 42 kW boiler is running the radiators - is less efficient than using a smaller boiler to do the same thing.

Another important thing to consider is the distance from the boiler or cylinder to the taps, and hence how long it will take for hot water to reach them.

 

[Tirglas_7]

Many thanks, So you're saying the unvented cylinder system is more efficient/cheaper to run than the combi?

Or do the pros and cons of each system mean they're about even?

As I say I'm looking fir the most cost effective system, including install and running costs