I need to replace my aging Vaillant combi with a new combi boiler. It needs to serve a three bed house with 9 radiators. I suppose a modern day Vaillant would probably require minimal re-jigging of pipework but I am just as interested in efficency/reliability. Many thanks.
If you are satisfied with the Vaillants flowrate then replace it for a condesning version. If you want a higher flowrate, Vaillants are not brilliant flowrates, then go for a Worcester Bosch Greestar 40kW or an Alpha CD50. Both of these may be larger than your existing boiler. The Alpha has a very good flowrate by storing water to assist, inside the combi case. Look at the web sites and see the sizes.
I think my present Vaillant's dhw flow is around 6-7 lpm. Going up to between 9 and 11 on the Turbomax range would be like heaven. I will have a look at the links you have provided. Thanks for the info.
Greenstar 16 litres/min CB50 approx 18-19 litres/min.
Using one of these will be heaven
I read a statement on a website that from 2006 the condensing boilers are going to be compulsory (I assume for new installations) - is this correct? Should I be looking at replacing with one of these (as you suggested in previous message)? I realise that they are supposed to be more energy efficient and environmentally friendly (apart from the condensate) but is it true thet they can be more troublesome (whatever that means), have a shorter life span, only work in condensing mode when the working conditions are correct and that the system may be to restricted if you have a lot of TRV's? Just quoting some info. from a website I was looking at. I haven't included the link as I don't want to get flamed.
The current intention is April this year (2005).
It can be a good idea, but check the specifications very carefully regarding flow rate. Pay particular attention to get the real numbers for any with internal storage. Seemingly good numbers are quoted in the marketing blurb, but these are for when the store is being used. When that runs out - which it will because most are 50 litres or less) the flow rate drops to whatever is implied by the boiler power output. If the manufacturer hasn't been honest enough to give the true figure, you can deduce it by comparing with equivalent power boilers from other manufacturers.
This is not to say that an internal store might not be useful, but do remember that you can't get a quart out of a pint pot.
All flow rates depend on the ability of the mains to deliver them.
There is a lot of misinformation on this. However:
- early generation UK designed and made condensing boilers did have reliability problems. Those from Holland and Germany were 3rd generation at least at that stage and reliable and in those countries condensing boilers have been used for 20 years.
- nowadays there is not a lot of complexity difference between a decent conventional boiler and decent condensing boiler. Even the UK ones have improved considerably - largely because firms have been acquired by German manufacturers in many cases.
- condensing boilers are more efficient anyway than quite recent conventional boilers. Efficiency increases at lower temperatures, and below the temperature at which condensing starts (about 54 degrees on the return), it increases more rapidly with falling temperature. It isn't the case that it's necessary for condensing to happen for there to be a benefit, and neither is it the case that some nirvana is reached when it happens. It's simply an increase in rate of efficency with falling temperature.
Could not agree more. My recently installed WB Greenstar 40 plus does not even need to get its full gear out for the 10l/min that my mains supplies. My plumber has a go at the stop tap as Yorkshire Water insists that the mains on street delivers 30l/min. But I really, really, really should have checked all this before.
Fred
??
You have replaced the stop c*ck?
Wrong. Most are 50-60. The Alpha is 57 litres. When the hot water is being drawn off, the boiler is also re-heating the incoming water fast too. You just don't get only 57 litres into your bath at the high flowrate, you get far more at the high flowrate. When the store is exhausted about 13-14 litres/min is produced. This will still fill an average modern bath (80-100 litres) pronto. The boiler re-heats the store of water in a matter of a few minutes.
............and on this ng too.
That's the conventional CB50. The condensing CD50 is 52 litres.
It can only add in heat at the max output rate of the boiler part.
You get *some* more. As soon as the initial pre-heated store is being used, the flow rate will begin to fall because you are taking energy out faster than it is going in. If the temperature is to remain constant, then the flow rate will automatically begin to fall.
There is a built in flow regulator, but it is thermostat rather than sensor controlled, so it would appear that the drop in flow rate will be sudden.
The CB50 produces a max of 28kW to hot water. This equates to 11.5 litres per minute.
The CD50 produces a max of 32kW to hot water. This equates to
13.1lpm, not 13-14.If you are going to quote specs. do read them properly and try to stick to one at a time rather than picking the most favourable figures from different models.
This may be the capacity of your bath, but standard ones require around 150 litres.
The manufacturer claims that the CD50 will "fully recharge the store" in "about 3 minutes" in the marketing blurb. However, in their specification that time is *only* if the boiler was firing and *only* to reach 70% of the total. Through a more realistic 50 degree rise in temperature of the store, it takes 7 minutes. The CB50 is even worse at 8 minutes.
There is marketing licence here to put it mildly.
Functionally this thing is like a system boiler with a built in small storage cylinder and nothing more than that. One might as well have a separate system boiler and decent sized cylinder and do the job properly.
It should also be mentioned that this is a pressurised cylinder product and will have to be professionally installed, tundish fitted and everything else required for a pressurised storage system.
You're telling me......
Not less than 50 as you implied
I would think so, unless you add your Ronson lighter to assist.
13.1 is between 13-14. It is isn't it?
..and he thinks he can count.
No. modern standard are 80-100. Get a new bath, a smaller one, you an environmental disaster area. A one family pollution machine.
I would not cal 7 minutes from bad. It is v good. As most of the time it will not be depleted re-heat is zippo.
That is all a combi is, with a water section added. Well spotted 10/10.
No. A combi then doesn't have the silly cylinders and tanks taking up space, and NEVER runs out of hot water.
No tundish as all taken care of inside the casing. I'm not sure if an unvented combi has to conform to BBA approval.
I am.
Granted, byt many have titchy little tanks and the purpose of those is quite different.
Don't use them.
It's very much closer to 13 than 14, so implying anything approaching
14 is misleading.
Better than you, it would appear.
No they are not. A standard bath requires 150 litres if you want more than a dribble in the bottom. If you want to use one with your knees under your chin, that's up to you - unless Archimedes principle helps you, of course.
It's neither bad nor good, but entirely predictable from the power. The point is that the marketing blurb, which you are using as reference, quotes only the best case. It will be depleted completely when a bath is run, or a decent shower used for a reasonable time.
This isn't even that - it's a system boiler with a cylinder in the box. It isn't even using the cylinder as a heatbank.
Oh good grief. Been drinking the Kool-Aid again? The small cylinder is inside the box rather than having a proper sized one separately. Unless you have away of compressing water in the liquid phase, then the space required for 50 litres of water doesn't change.
"Never runs out of hot water" is a marketing bullshit claim.
I can achieve precisely the same thing with a conventional fast recovery cylinder under the same flow-reduced operating conditions.
Go and read the installation book.
A tundish is required and it does fall under building control for installation (and I don't mean just part L1).
Try reading the specs rather than the glossy, and also look at one product at a time so that you don't confuse yourself.
You are on about combi's that have dead leg draw-off lag reduction. Not the same thing, althiough a largeer stored water combi would do the same thing.
Tsk, tsk. At 18 litres/min draw-off that will exhaust the store in approx 3 mins, but it is being re-heated at 13 litres/min at the same time. So, approx an extra 2 mins 18 l/min, which delivers approx 90 litres at a high flowrate. After the store is exhausted the flow reduced to an infinitely continuous 13 litres plus for ever. So, an average sized bath can be filled as quick as a normal cylinder tank setup, when you take into account cold has to be added too.
There you are.
As soon as the initial pre-heated store is
On what do you base this article of faith?
But it does deliver an average bath at high flowrates and drop to a 2nd stage flowrate for ever. It never runs out. Got it?
No, an actuallity, unless a) the combi brakes down b) the gas cut off c) the wateris cut off.
But you have a separate cylinder with all the controls, taking up space, adding complexity with external zone valves, stats, etc, and looks ugly like a school boiler house, gives no more than good high flow combi. Appalling. A high flow combi is a neat all in one case. Fabulous.
The OP wants to know the best combi. A high flow combi will be wonderful for him. The business. He can also look at the W-B 440 high flow combi too. Fabulous.
This statement (with regard to the Alpha), always strikes me as disingenious.
You are technically correct that it will not stop producing hot water. However, as has been pointed out, there will be a time when its flow rate drops significantly. One must also presume that its temperature will also drop given that the temperature of the store may be higher than that which the boiler can susstain for heating cold mains water on an ongoing basis once the store is exhaused.
So if you start running a bath (especially a normal bath, and not an IMM special "micro bath"), with 65 degree hot water from the boiler mixed with (say) 40% cold water, you are going to need to sit there at watch for the point it runs out of accumulated hot water, otherwise you are going to return to a bath where the last third has been mixed from 40% hot water at 40 degrees, mixed with 60% cold! i.e. 'kin freezing.
Similar story in the shower... if you have a fast reacting thermostatic one you may get away with just a drop in flow rate, but chances are you will get a least a spell of cold water.
I am not suggesting the Alpha is neccesarily a poor product, it may in fact be very good and well suited to some installations. So why the continual overselling of it as a cure to all combi ils?
That would assume no internal mixing of the water in the little cylinder which is not the case, especially since it is so small.
Even the manufacturer doesn't believe that because they put the thermostat to control flow rate reduction near the bottom.
Plus 0.1. That's it.
You have to add cold in either case......
This is nonsense.
It's called measurement as opposed to your assertions which certainly are an article of faith.
It delivers part of an average bath at 18lpm and the rest at 13lpm.
The implication of what you say is that a conventional cylinder would run out. If the flow rate is reduced to a similar level, the water from that would never run out either. Of course, with a proper sized cylinder, the issue doesn't arise anyway.
It's a marketing bullshit claim that can be equally applied to any system where the flow rate is reduced to match power input.
I'm surprised that you fall for this nonsense.
Actually, perhaps I'm not.
Yours may look like that - mine is pretty neat because I took time and trouble over it and followed the manufacturer's instructions.
Of course it's totally untrue that an external cylinder does not give more than the combi you describe. The storage capacity is larger.
I wouldn't regard a huge, heavy box like this "neat".
It may or may not be. I am simply pointing out the potential shortcomings that of course are not mentioned in the manufacturer's brochure and have to be deduced from the spec. sheet.
That is not to say that the product may not be suitable, but it is not necessarily the best thing since Adam had intercourse with Eve.
Does it say so in the brochure? That's good.
This product at least has the store used as a heatbank, although isn't small.
They don't cover the fact that it is a two stage flowrate setup. The pint is that in norm al one bathroom average house usage it will be turning out at high flowrate for approx 95% plus of the time it is used. It can also be used for a two bathroom house, as long as the baths are not filed at the same time. Fill one and it recovers in minutes and fill the other.
My sister has a full 2 bathroom house and in 20 years, with teenage kids, has never filled two baths at the same time. The house was fitted with
300-350 litre cylinder that was in reality was overkill storing hot water that loses heat to standing losses. When it was replaced a smaller quick recovery cylinder went in. They have never ran out of hot water with the smaller cylinder.The normal combi situation then, which is not a problem to countless millions all over the world.
A modern average bath is now 80-100 litres. That is "not" my assessment.
Again not the case
It is one of many. There is one poster here who has a hate campaign against it. It does deliver. In normal everyday usage they do deliver. See, one happy user:
From: Jape ( snipped-for-privacy@ecclesall.demon.co.uk) Subject: Re: Most powerful combi boiler Newsgroups: uk.d-i-y Date: 2005-01-07 01:02:05 PST
I've had fitted an alpha cb50 for exactly those reasons and it fits the bill perfectly
Shower will take your skin off, and bath fills v quickly with scaldingly hot water (you can of course turn the thermostat down)
Making things up again.
Seek professional advise.
Can't see that... I have never seen one of your 80-100L baths installed in a real house, hence you will be using both flow rates every time you fill a bath.
Huh? nonsense.
With a normal combi you turn on the tap and water will come out at a temperature. Come back 20 mins later at it will still be producing water at the same rate and flow. The Alpha however will not - the flow will have fallen as will the temperature.
You keep repeating it and it is still wrong...
I just had a look at the Armitage Shanks site - they have some 20 baths listed - appart from one one "shower tub" and one extra short 1.5m bath all of the others held significantly more than 80 - 100L
What sort of average are you computing?
Also when are you going to realise that "most" houses do not have an "average modern bath" anyway, they have the same bath that was installed
10 to 20 years ago! Not everyone rips and replaces their bathroom every five years.More importantly, why when attempting to advise on things like tank size (be it built into a boiler or not) do you not ask the poster what capacity bath thay actually have? Rather than making an assumption designed to reflect your advice in the best possible terms?
I am not what?
Think it through and do the sums...
The hot drops in flow rate and temperature, in the case of flow rate this is a step change. Please explain the logic of your statement?
Do the sums.
Hasn't helped you, has it?
I'm sure you never used UFH too, but it is there.
No it isn't a problem at all. Millions use combi's and love them
assessment.
It IS correct!!!! Maybe not in your hosue.
I know many who do. Avocado is trendy at the mo.
An Alpha will fill a 130 litre bath very quick despite dropping to the lower stage flowrate for the latter part of the fill. This you can't get your head around. You certainly have no experinece of such a combi either,. So don't make things up.
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