Combi boiler size and efficiency

Hi,

I'm trying to decide on which combi boiler to fit in a 1 bedroom house with one bathroom with bath/shower (I may add a shower room in the future) and three 600x1000mm double radiators. I've been looking at the Ferroli Optimax II HE combi as the depth is small enough to be located in a cupboard space and it has a 5 year warranty.

This combi comes in 18S, 25S, 31C etc. capacities. I've read conflicting things such as "if it's too powerful, it'll always be cycling on/off which will be less efficient" and "the power of most combis can be adjusted so overpowered ones can be just as efficient".

I've had one quote recommending the 18 and another recommending the 25. Is there any advantage to getting the more powerful model? e.g. would I get hot water faster for a bath? The price difference between each isn't much. This particular boiler seems to be gas modulator which I believe means it will be efficient in low use.

I've also read that high capacity radiators are best as it lowers the return water temperature (thanks bengasman!), increasing efficiency. I'm planning to slightly oversize my new radiators because of this.

Thanks.

Firstly it sounds as if you are a bit confused as to waht boiler you want!

The 18S & 25S are system boilers and not a combi's, as denoted by the 'S' on the end.

The 31C is a combi, as denoted by the 'C' on the end.

Have you a hot water cylinder or do you actually want a combi that heats the water instantly?

If you have a hot water cylinder then all you will need is approx 9-12 Kw system boiler, if you want a combi then if you shower mainly a 24Kw or maybe a 28Kw if you have baths will suffice.

Your installer will range rate the boiler down for the ch, whatever size you get.

Combi's are sized by your hot water needs, not ch needs.

Have a look at the Broag Avanta Plus range, excellent all round boilers and very small. Find a Broag installer like me and you will get a full 5 year parts and labour warranty as standard for no extra cost.

gas4you said:

Firstly it sounds as if you are a bit confused as to waht boiler you want!

The 18S & 25S are system boilers and not a combi's, as denoted by the 'S' on the end.

The 31C is a combi, as denoted by the 'C' on the end.

Have you a hot water cylinder or do you actually want a combi that heats the water instantly?

Click to expand...

Oops, I meant list combi choices only. Didn't notice those were system boilers.

If you have a hot water cylinder then all you will need is approx 9-12 Kw system boiler, if you want a combi then if you shower mainly a 24Kw or maybe a 28Kw if you have baths will suffice.

Your installer will range rate the boiler down for the ch, whatever size you get.

Click to expand...

Ok, the one I was looking at is a 31C. If that just means I'll get a better bath flow rate then that seems fine then.

Combi's are sized by your hot water needs, not ch needs.

Have a look at the Broag Avanta Plus range, excellent all round boilers and very small. Find a Broag installer like me and you will get a full 5 year parts and labour warranty as standard for no extra cost.

Click to expand...

Thanks, I'll look into this. Cheers for the advice!

definately would NOT fit a 24Kw a minimum of 28Kw will give you good hot water.
if you really want a cheapo boiler then i would say look at the Halstead Eden around the same price as the Ferroli but I have found them to be better.

you get what you pay for as they say and these are the better cheap end boilers.
Avoid Ideal as they are poorly built and their warranty policy stinks!!

Here`s some great advice. Don`t fit a Ferroli boiler ever because they are cheap sh*ite, if you want to throw your money away go to BnQ and buy a Heatline or Ravenheat, Sh*te.

Invest in a decent boiler, you can get a decent Baxi boiler for around 800 squids.Good warranty also. Boiler is only good as the installer, check credentials, don`t get your mate who knows someone who fits boilers dead cheap, or you will get a lifetime of trouble with no comebacks. Do it once. Do it right.Remember, think once, think twice, think BOILER. Look left, look right, look left again, look for big bloke in spandex with big green cross on his chest. Run away quickly. He is a dangerous mental person.

28kw would be a good size combi.

also if you are worried about on/off cycling then I would look at what the min ch output is and fitting modulating controls such as open-therm and weather compensation.