30kW System Boiler Choice

28 Feb 2008
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United Kingdom
I am just about to get rid of our old Baxi Solo 15kW Boiler for a more efficient model. The house is 19 years old and is a 4 Bed detached and has had a large extension of the kitchen and dining room.

I am going to have a 30kW system boiler fitted to get rid of the F&E Tank.

I am looking at the Vaillant ecoTEC Plus System 630, the Worcester Greenstar System 30CDi or the Alpha System InTEC 28S.

Anyone got any recommendations from these. The Which? Magazine lists the Vaillant as a Best Buy. The Alpha is the cheapest but I'm not driven just by the lowest price. I want the most reliable and efficient as well as a competitive price. Any comments welcome.

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A qualified plumber who also teaches plumbing has sized the Boiler and will also fit it.
I just wanted the opinions of the people from the Forum on the three Boiler choices. The Plumber will fit what I want, but he has steered me towards an Alpha.

I wpuld take advice of your installer, since you have expressed such faith in him. Or maybe not.....

I may not be as clever as your installer, but would ask you to consider the following;

Boilers are sized for the external temperature being -2C. We assume that you may want to get the house to 21C. So on the coldest days (eg. When it is -2C outside) you boiler needs to add 23C of heat energy into the house.

If you have a 15kW boiler at the moment, and if your installer is correct about his sizing calculations needing 30kW, on a cold day your house will only reach 9.5C indoors.

So i think you have been misinformed by a fool. Choose another installer, most of us are cleverer than your training chap, who I assume teaches 'career change chancers' as he wouldn't last long in front of a pro.
thats generous Dan, I'd say 15+3kws for the extension, as the original was almost certainly correctly sized
The house is 19 years old and is a 4 Bed detached and has had a large extension of the kitchen and dining room

Funnily enough almost exactly the same as my house. Which had a 12kW boiler in it IIRC. It was perfectly adequate.

*edit - just checked and I had an Elan 50P when we moved in - so 14kW.
Simond is showing an amazing lack of how central heating works to say the house would only get to 9.5 degrees .
Properly designed heating gets the house up to 21 degrees in an HOUR when it is minus 1 outside that does not mean a boiler half recommended size would only ge tit to around half this temp it just means it would take far longer to get to a higher temp.
But from a 15kw boiler to a 30 kw is a fair size jump and does sound excessive for a 4 bed house.

As for a boiler the baxi megaflo is a good system boiler.And reasonably priced
Before you fit the system boiler tie up your ball valve for a week or so to make sure you dont have any pre existing leaks on your system (do it with system cold)
design criteria was/is two hours from cold....all a bit silly..

Boilers are regularly oversized compared to real heat load and heat emitting capacity....

It would make more sense to size boilers to radiator output...

Oversizing only benefits the manufacturers in extra profits and offers no benefit to the end user..
I am sorry but I cannot believe the arrogance of some people on this Forum and how an argument can start from a very simple question !!!

All I wanted was a simple view/opinion of the quality of three System Boilers, a Worcester, a Vaillant and an Alpha. If people don't know these Boilers and have no experience of these them, then don't post a reply.

Why do people feel they need to ask all sorts of technical questions.

The Boiler size is whatever I tell you it is. I just want to try and find out from those who might have experience, the merits of each Boiler type I mentioned. Obviously from the posts so far nobody has any idea.

Forget it !!!

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