Oversized Boiler

[FrankTrent]

I'v had 3 quotes for a replacement boiler and replacing pipework on one-pipe system conventional vented by a 2 pipe system.. The old rads (1965) seem OK & will stay).
I've been quoted on a W Bosch 18Ri by B Gas, another on a 24i System and now the 3rd plumber says system boiler is too risky on old rads and he can see I need a W Bosch 30CD (just by 'experience').
I calculate the requirement as no more than 16 at tops. What is the likely problem if I have the 30CD...will it be inefficient.
The other 2 are W Bosch approved installers, and appear to know what they are talking about.

 

[mickyg]

what boiler do you have now? does it heat the radiators sufficiently?

 

[FrankTrent]

Its a Potterton Kingfisher II CF 50 installed 1990. Heat output 40,000 - 50,000 BTU. It works well and is normally set at '2' 9it goes up to 4).
I just want to update evrything due to house alterations.

 

[mickyg]

your current boiler is about 16kw, if it is sufficient for the demand then there is no need to go bigger. the guys suggesting 24 and 30kw boilers are muppets, and if anything you will just lose efficiency. You want to go as low as what will be adequate to get the most efficiency. You will probably get away with a 15kw boiler.

 

[powell30]

Why spend all that money on a new boiler and not replace the rads (1965)??!!! by the time they have been flushed the cost of that alone will nearly cover the replacement......

 

[Agile]

I would never change rads for the sake of it.

We would charge about £200 each and that will be a considerable cost.

There is no need to have an oversized boiler but the 24kW upwards were advising a combi boiler.

Tony

 

[doitall]

50000 btu's_ 14.6 Kw so as Mickyg wrote 15-18Kw is plenty.

45 year old rads I would seriously consider getting rid off, modern rads are far more efficient.

But whatever you do, on an old system a Magnaclean is a lifesaver for the new boiler.

 

[Agile]

Some 45 year old rads are cleaner than two year old rads.

Probably because 45 years ago they did the pipework in the correct positions!

If the heat output is sufficient then I dont see any need to change.

If the heat is a bit low then I usually advise adding an additional rad in a central area.

Tony

 

[FrankTrent]

Thanks for all the replies. My current boiler is 50,000 btu which is 14.64 kw. My own calculation makes me think that I will be OK with an 18ri.
I have phoned W Bosch Technical and they confirm that if old boiler is IK then I can do a like for like swap so I'm going for a 18Ri 61,416 btu (and a serious chat with the installer).