choosing boiler

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.

  1. 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?

  2. 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 ?

  1. Is there a site/resource which has a design layout and wiring etc. available?

Thank you, Neil

Reply to
Niel A. Farrow
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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.

Reply to
Christian McArdle

No, it's perfectly fine unless you go to something ridiculously large.

I believe that their program does the traditional notion of adding in about 4kW for the cylinder plus 20% margin. You may also have the adder factor for intermittent heating.

Nowadays, the more typical design is to use hot water priority with a diverter valve. This means that the default is running the heating and when there is hot water demand, you switch the boiler over to the hot water cylinder. If you are using a cylinder to part L1 of the Building Regs. (you can generally only buy at least that), then it can use about 15kW of heat from the boiler and reheats reasonably quickly

- so the notion of the 4kW for the cylinder isn't really needed. You take the boiler off line from the heating for a short time. A better bet is to use a fast recovery cylinder, which is able to use over 20kW. Some boilers even have a capability of a higher maximum output for driving the cylinder.

So you could consider changing the cylinder - it's not that expensive

- if not, you can still design for the HW priority arrangement and perhaps change it later. It's only if you have a controls arrangement where both the heating and the HW can demand simultaneously that you need to allow for it with the boiler.

Vaillant generally receives good press here. Why not go for a condensing model, though. The boilers that you mention are at close to the bottom of the allowable energy efficiency range of 78%.

Vaillant have some corresponding condensing models(Ecomax), or several people here have had good success with the Keston Celsius 25 - which meets your requirements and can be had for about £650. Seasonal efficiency is in the 90% area, so you can works out that the payback will be comfortably within the boiler range. This one also modulates down to 7kW whereas the Vaillant to 13kW.

Honeywell's web site has wiring diagrams for their various control plans. Y plan or possibly S plan are the typical ones and are industry standard.

.andy

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Reply to
Andy Hall

Did consider this but the condensers are about £300 more! Thank you, Neil

Reply to
Niel A. Farrow

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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Reply to
Andy Hall

Water heating counts as a 'zone' so for 3 or more zones S plan is the way. Y-plan is a sophisticated but in elegant solution to controlling a water and/or heating with only one motorized valve.

Reply to
Ed Sirett

Look at Keston boilers, and their site

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which has lots of info and diagrams and manuals. I have a Keston and am impressed. Richard

Reply to
Richard

The Ideal Icos is 670 quid for the 18kW modulating version, which is 120 quid more than the Thermocompact. Same for the Glowworm 18HXi.

Christian.

Reply to
Christian McArdle

The Glow Worm condenser is good and cheaper again:

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Reply to
IMM

The Glow Worm system boiler is cheaper than the heating boiler.

Reply to
IMM

Best use a proper quick recovery coil cylinder and a DHW priority system.

Reply to
IMM

Which is exactly what I went on to say........

.andy

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Reply to
Andy Hall

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..
Reply to
BillR

Payback is roughly 3 years.

Who told you that? More like 20 years.

Yes.

Reply to
IMM

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.

Reply to
Christian McArdle

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.

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paragraph 70.

.andy

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Reply to
Andy Hall

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?

Reply to
Dave Plowman

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>

Reply to
IMM

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.

Reply to
IMM

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.

Reply to
Dave Plowman

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