choosing boiler

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Need to buy a new boiler for my 3 bed end semi. Heatloss by the Myson program is 14 Kw and says I need a 22 Kw boiler.
a) Want a fully modulating system boiler (not a combi) which has bypass, expansion tank (no header tank in loft), pump, frost stat etc. built in. b) Will have 2 zones, upstairs and downstairs c) Some extra capacity for possible loft conversion.
Questions. 1. Is having too much capacity and a modulating boiler ok - have heard that too big a non-modulating boiler is not efficient.
2. Do I need the extra 8Kw that the Myson program says. Do most modern installations just give priority to the heating then switch on the hot water?
3. Valliant thermocompact 620 (20Kw / 550) and 615 (15Kw/460) vs Ferroli Tempra II 24 (24Kw / 463) and 18 (18Kw / 422).
Which best suites my needs and is the best system ?
4. Is there a site/resource which has a design layout and wiring etc. available?
Thank you, Neil
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It should be fine. However, see how low the boiler will modulate. This is particularly important on modern systems with TRVs or subzoning, as the heat requirement in marginal conditions may be quite low. If the boiler can modulate down to the low level, it will be more efficient.

Yes. It is good to have a reasonable over capacity when specifying a modulating boiler, provided you don't compromise on the low range of the modulation. It allows for future expansion.
It is actually normal to have priority to the hot water than to the heating, provided you have a rapid recovery cylinder. The cylinder can be reheated in 15 minutes, then the heating comes back on.
However, it is possible to have a system that doesn't give priority at all, particularly if the boiler is sufficiently overspecced to give good recovery AND power the radiators simultaneously.

Consider a condensing boiler, too. For an extra 100 quid or so, you'll get much better fuel economy.
Christian.
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Did consider this but the condensers are about 300 more! Thank you, Neil
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On Wed, 7 Jan 2004 19:47:44 +0000 (UTC), snipped-for-privacy@alumni.caltech.edu (Niel A. Farrow) wrote:

You can have a Keston Celsius for 797, Neil, or a Worcester Bosch Greenstar for 750.
If you're planning to keep the house for a while then this would pay back, even if gas prices don't increase, which undoubtedly they will.
.andy
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(Niel

get
The Glow Worm condenser is good and cheaper again: http://www.discountedheating.co.uk
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IMM wrote:

All of the above seem to me to be at least 300 quid more than what you can get a good combi for.
I too would consider a condenser but have yet to be convinced about the payback. I have 4 bed well-insulated detached house. Gas bills for CH & HW are only 350/year with currently an old conventional vented system. Even if I saved 10% a year, which seems unlikely, that's quite a few years to payback the difference in price of a condenser. As new boilers seem to only last 10 years max without major problems, will it even payback before it needs replacing I ask myself.. If we are thinking of moving within the next 5 years then the investment in a condenser will look even less attractive..
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(Niel

saved
Payback is roughly 3 years.

Who told you that? More like 20 years.

Yes.
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What is your boiler? Against a typical older traditional boiler, you'll save around 35%. Against a modern traditional boiler, you'll save around 12%.
So, with a modern traditional boiler, you should get about 292 pounds per year. With a modern condensing type, you should get about 250 pounds per year. Over ten years, this would save over 400 quid, which is several times the difference in price between similar quality new condensing and non-condensing types. Also, the difference in carbon emmisions over the complete cycle will be even greater, so there will be a considerable net benefit to the environment as well as your pocket.
Non condensing boilers will shortly be effectively banned.
Christian.
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I've got a Potterton Kingfisher floor standing balanced flue, which still works perfectly, although over 25 years old. It's situated in the bathroom in an enclosure which doubles as an airing cupboard, so there's no waste heat really from the direct heat from the boiler itself. I realise it's not going to last for ever, though. What sort of percentage savings would I get by changing to a condenser - remembering that I like the bathroom hot at all times?
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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But the majority of the waste is going out the flue in the gushing flow of 2-300C waste gases, replaced by an equal flow of freezing cold outside air being drawn through into the house due to the open flue not providing a dedicated air supply. That is the main difference.
I don't know if the SEDBUK calculation allows for case losses as being a useful gain, anyway.
Christian.
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Err, it's a balanced flue.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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Even so, the waste gases are much hotter than with a condensing type. This is the major energy efficiency difference. If the boiler actually condenses internally, it is even better, because as well as the temperature difference, you get the latent heat of condensation added to the equation.
Christian.
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On Thu, 08 Jan 2004 12:52:14 +0000 (GMT), Dave Plowman

Don't forget that most of the loss from the boiler is what is going out of the flue......
From the SEDBUK list, there have been several generations of Kingfishers, but the older ones are going to be around 65% efficient, possibly even less.
I changed from a 65% efficient Glow Worm to a 91% condensor and achieve between 25 and 30% better fuel economy - pretty much in line with what SEDBUK say.
As far as the bathroom is concerned, you might need to add in a radiator, perhaps in the airing cupboard, to release the equivalent heat in the room.
.andy
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wrote:

around
bathroom
You have take into account that this fellow hasn't serviced his boiler for 20 years. He boasted about the fact. So he would save a ton of money on installing condenser and with the money he saves he can go out and buy many pairs of yellow DeWalt boots...and the odd bright yellow cap too. Look just the part in the ale house leaning on the bar.
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years
save
times
A good point. Like double glazing, people became aware and drop the [rice of a house if it is not there, or insist on it being there. The same will probably apply to boilers. If a plume they will buy, or drop the price to replace the boiler or insist one be fitted. Just like DG>
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I take it you live in an economically depressed part of the country, or an undesirable area to actually live in?
You can insist on whatever you want when trying to buy a house. And the owner will also insist on selling to someone else...
What most people consider as double glazing - ie those horrid PVC things - will actually *reduce* the value of a house in this area.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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Sorry, but virtually no one takes any notice of the boiler when they buy a house. Providing it works and isn't identified as just about to die, then what colour it's been painted would be a more significant factor than if it's condensing or not.
I have seen one report that a surveyor actually warned that a condensing boiler had a significantly higher maintenance cost, so in this case it was regarded as a negative factor.
--
Andrew Gabriel

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writes:

[rice
will
to
You didn't get the point. When it's mandatory and only condensers are available people will know this, and they can readily identify a condenser by the plume. It should go the same way as DG in customer awareness. Financially DG is not worth it for the energy it saves. A super long payback, yet people like the idea of sealed windows and are prepared to pay for it.

No accounting for a dickhead surveyor. I never met a surveyor who anything about CH, DHW or gas in any sort of detail to pass any relevant comment. It is not their field. They are good at concrete.
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wrote:

You won't get a "good" combi for 350 - you might get an adequate one that will last for a short to medium period of time.

It depends on the age and efficiency of the boiler. The typical conventional one of a few years ago had a SEDBUK efficiency of around 65%. Most recent ones are just scraping into the 78% level in order that they may still be legally installed. A condensing model will achieve 90-91% on this scale.
I did a change from a 65% model to a condensing boiler a year and a bit ago and the energy savings are the predicted 25-30% range.

If you buy a decent one, then it should last for 20. The price of gas will undoubtedly increase during that period or even over 10 years.

Possibly true. However, it is likely with the next round of changes to the Building Regulations with respect to energy conservation, that the minimum efficiency allowed will be 86%. This will make this discussion academic since conventional technology boilers would be off the market. Current government indication is that they would like to do this next year.
http://tinyurl.com/2mgfp paragraph 70.
.andy
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can
only
saved
will
in
Also, when all boiler are condensing units the price's will come down, as boilers are very competitive in the UK market with 1.3 million each year sold.

Isn't Tony brilliant for doing all this for us. Great guy! The best we have had.
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