designing a central heating and hotwater system

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hi,
Any recommendations for sources of information on designing a central heating/hotwater system for please.
have found sites that provide info on rating the boiler/rads but nothing on the actual design. type of heat storage etc.
duncan
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cheers Andy
i'll go have a look at that one.
I'm more than happy with the installation side soldering etc. just need the detail to get things right with for upto date specs etc.
duncan
wrote:

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What do you intend to do? As you are a DIYer go the combi route. Buy a high flowrate combi. Not all combi's give a trickle for hot water. They are easy to install with minium design in CH pipework and rad sizing. You connect up 5 pipes, run a power supply and a wire for a thermostat or thermostat/clock from the combi. Superb for high pressure showers. A doddle.
Don't go for complicated cylinders, tanks, motorised valves, control systems, etc when there is no need to. The rad sizing can be done by using one of the many on-line rad calulators. No need to size a combi boiler as it will do 80-90% of most UK homes the CH output is so high. Any further points ask me.
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How is recommending the best rote for a DIYer a put down. This is uk.d-i-y.

A one box solution that professional experts have incorporated all the design and components is by far the best option.

That's why I said get back to me.

They give a good ballpark figure.
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I would disagree about the "ball park figure" being adequate to start with, the odds are you will end up with a boiler and radiators which are too small. Bigger IMO works best for heating systems, this applies to boiler and radiators. Of more importance, where are the 10 year maintenance and running costs factored in on a combi system without soft water. How do these costs compare with a traditional conventional vented boiler, even allowing for a tank replacement every 10 years? Thinking about it, are there any boilers of any type with a 10 year warranty even with soft water? In the past, my boiler life achievements were in excess of 20 years, have these days gone forever?
Regards Capitol
IMM wrote in message ...

snip
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Ballpark is fine. There are a few on-line calculators. It is best to use a few. Ad 5 to 10 % extra if you like.

The smallest of comi's will do the CH on a "very" large house. The boiler sizing is not a problem if it is not a big house.

Always have a de-scaler on a combi, or on "any" system in hard water.

Firstly, a combi is a system boiler with a water section. Many share the same components. Secondly, a combi has most of the "system" in one box. Only the rads and a wall stat are ouside the box. So when you start comparing breakdowns and longevity compare like with like. On a cylinder/tank set up include any problems with the F&E tank, the cold water storage tanks, the cylinder, the 3-way zone valve, the cylinder stat, the programmer, all the associated pipework, etc. Then you will find that a combi is no less reliable, and get a good make of combi, probably far more reliable overall.
Got it? :)
I had a Potterton Neatheat for over 20 years. The boiler was very reliable in itself because there was not much in it. In that time I went through 3 pumps, a zone valve, a zone valve motor, a cylinder, cylinder stat, room stat and a programmer. On the boiler a relay, flue fan and a pressure differential switch. Overall the "system" was not that reliable. I am certain a good Vaillant would have given far less trouble over 20 years.
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IMM wrote in message ...

a
Sadly not true, as our friend has found out the hard way!

Combis with descalers in hard water areas, don't generally seem to give 10 years service. All my friends with new boilers are getting less than 10 years life from their modern boilers.

Where are the manufacturers offering a 10year warranty?

I would regard that as being totally unreliable, only one pump at most would be necessary on a reliable system.

Regards Capitol
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use
boiler
Please read again. The smallest combi is approx 80,000 Btu/hr, which is big enough for a largish 4/5 bedroomed house. Most houses in the Uk are a lot smaller than that. The average sized combi is approx 95,000 btu/hr. They must have a large house or one with no insulation.

Why are they being scrapped? In many cases they are being replaced because the replacement cost is so low compared to fixing. Also the newer combi's work better, and give better flowrates, than a 10 year older. A combi can be bought for approx 350 in trade places, and 400 off-the-shelf in B&Q. A 13 litre/min can be bought in Wickes with all the trimmings. Combi prices have tumbled. They are so cost effective it is worth putting in two in a 2 bath house, with one doing upstairs heating and the other doing down.

Many give 5 years on the heat exchangers. I think Vaillant give 3 or 5 years on the whole combi. Many give 2 year guarantees.

reliable
3
But average for a tank/cylinder setup over 20 years!!!

Over 20 years? I would say 2 pumps. I have seen few pumps go beyond 10 years.
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IMM wrote in message ...

big
It's taken me some time to check the figures quoted above. The range of common condensing combi boilers is 75Kbtu/hr to 156Kbtu/hr. The central heating output of these units however varies from 53Kbtu/hr to 156Kbtu/hr. Small units cannot be relied upon to cope with a 4 bedroomed house in winter. The figures are from the architectural digest, so I have no reason to doubt them. The house is modern with insulation to the relevant standard. Looking at the heat exchanger materials, with some manufacturers using copper and aluminium, I'd be very surprised if the average life expectancy would ever exceed 10 years for these units. I guess that is why better manufacturers use stainless steel. The figures for water delivery at 35C rise are in the region of 10L/min for most of the units. 17 minutes to fill the bath! I still think that an ion exchange water softener is essential in hard water areas.
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The CH output is generally lower than the hot water output to reduce boiler cycling as in 90% plus of cases the boiler, for CH purpose, is too large. In most cases the CHG output can be raised to hot water output. Very few combi's fitted are 53,000 btu/hr. The average is way above that. Go to B&Q and you will see a 80-85,000 btu/hr off-the-shelf BIASI combi, for 400.

The super small ones of 53,000 btus, no. But I have never actually come across one of these and they are not the normal units you will see on sale. An average run of the mill combi that is fitted in most homes? It will cope with power to spare.

Neither have I, but they are so vague as to be useless giving only the highs and the lows The average combi fitted in UK homes will cope with a 4 bed house.

How modern? Insulation regs have risen recently and progressively risen since the regs first insisted on insulation in 1974. Many people would consider an insulationless 1973 house modern. What is the CH rating of the house in btu/hr?

On what experience/figurers do you base this assumption? A copper/alum' heat exchanger will last 20 years plus if the installation is fitted right and serviced right too. A boiler with the burner pressure far too high may not last that long (poor servicing). Modulating burners have helped improve longevity. Electronic controls on some boilers (combi and system) will lock out if the burner pressures are way out. BTW, in most cases the same heat exchangers are in the system boilers. Makers use the same exchangers and add a water section to make a combi. Many condensing boilers have the same exchangers as combi's and system boilers and add a smaller condensing exchanger. They keep their production lines and component counts down.

Stainless is becoming more common and 5 year guarantees are given, even with the Hepworth cheapie from Travis Perkins. Yet, the reason why many combi's are scrapped is not that the heat exchanger has burnt out. It is because of other factors, the biggest is ignorance of the combi operation by "plumbers". In many cases it is that the repair cost is not far off a new combi as they have tumbled in price, with many being below the price of many system boilers. Also a new combi will invariably have a better flow rate, be physically smaller and probably a faster response rate with pre-heat exchangers or built-in water store vessels.

And your point? 10l/min is the rate for the cheap end of combi's. Flowrates far in excess of this are available, even up to two bathroom jobs (well 1.5 and 2 with a push). A Worcester HighFlow will fill bah in 5 mins, as will many other high flow combi's. 17 minutes to fill a bath? Even if the temp coming out is at bath temp of 45C that is 10 minutes fillup, as 100 litres is the average bath capacity. After all you are on about "most" here, and most baths will be 100 litres. If the combi is delivering hot water at above 45C then 7 to 8 mins fill up time. Then get a 18-19 litres/min combi and the fill up time is 4-5 mins. Wickes even sell a 13 L/min off-the-shelf combi for 525. At these prices you can afford to buy two combi's and have one do upstairs and one down for natural zoning and split the bathrooms. Highly cost effective.
And the pumpless high pressure showers in all combi's are for free.
Don't go on old wives tales and ignorant "plumbers", who are very good at drains and gutters. Go to heating engineers.
Many combi's are designed for ease of design and installation, true DIY. For e.g., the Ariston Microgenus even has a built-in filing loop and pressure differential valve, among other failsafe goodies. These are combi's are designed for people with a limited knowledge of heating and are the models DIYers should aim for.

Not so. A phosphor descaler will do. They are very effective in eliminating scale, or at least 98% of it. Any scale left around is easily removed by normal washing.
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"IMM" wrote | > >Don't go for complicated cylinders, tanks, motorised valves, | > >control systems, etc when there is no need to. | > Come on. It's not that difficult. | A one box solution that professional experts have incorporated | all the design and components is by far the best option.
<giggles>
Microsoft
<runs away>
Owain
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Because you are suggesting that a single box combi solution is the most appropriate for a DIYer on the basis that it is apparently simple.
The reality, of course is that there are a whole load of issues such as incoming water mains pressure and flow, appropriate sizing of pipework, flow restrictors and a whole raft of other issues to deal with to make it work properly.
You don't know what the usage requirements are so how can you be so sure that this is the right solution. Why not a thermal store, or have you gone off those this week?

You know full well that there is more to it than that.

I have seen U values in at least one that are out by a factor of 3:1 on a material that mattered. This led to a 2:1 discrepancy with calculating by hand using the Building Regs numbers. The latter was correct.
That is not to say that the programs arenot useful, but just using them blindly without understanding the maths that they are doing is a recipe for problems.
On an investment of this size in money and time, it makes more sense to sit down for a couple of hours with a piece of paper and a calculator and to check properly.

.andy
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uk.d-i-y.
You are getting there. It is simple. And..will most likely fit the bill.

That is why I said get back to me.

That is why I said get back to me.

Not much more. So no need to complicate matters and best buy the ideal, simple, one-box, off-the-shelf solution. Clever people these boiler engineers.
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But doesn't answer the question which was asked, which was how to go about designing the complete system.
That certainly is not a case of trotting along to B&Q, buying a combi boiler, a few radiators and plumbing bits and sticking it all together and hoping.
Radiator and pipework sizing need to be done properly whichever solution is chosen.
For a combi boiler of sensible capacity to be useful, it is often necessary to upgrade the gas supply from the meter - this may be non trivial. The water main may need to be upgraded, also non-trivial. If there is existing internal pipework for hot and cold water, it is likely to need modification and re-routing in order for the relative flows to work reasonably well. Flow restrictors may need to be fitted, etc. etc.
A conventional boiler and system may be more suitable since it is likely that none of the above issues will need to be addressed. If somebody is capable of working out radiator, boiler and pipe sizing correctly and of doing the required plumbing work properly (which would need to be done whatever the system) then fitting of a pump, motorised valves and cylinder and tank are not a stretch of ability or intellect. It is also a more scalable solution in terms of meeting a range of requirements.

Clever enough not to assume that one size and one technology fits all.
.andy
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wrote:

It does answer the Q. Most of the design is inside the box, done by experts. The only design is the rad sizing and the pipe run. Not difficult.

Not hoping. It is not far off what you say. Just a combi with the correct flowrate and size the rads and buy them.

That is why I said get back to me.

One pipe run is trivial, when looking at the whole system.

It may not need an upgrade.

It may only require a small modification. Flow restrictors on all taps are easy and cheap to fit.

Maybe, but unlikely.
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Sorry I don't buy that. From the high level functional point of view, the combi is simply bringing into the box the pump and an alternative means of providing the hot water. Granted, it does reduce the component count vs. a cylinder system.
However, from a *design* perspective, there is little or nothing involved in provisioning a vented cylinder, motorised valve(s) and pump. One is going to choose a suitably sized cylinder for the application, hopefully of a fast recovery type. The only design decision there is to try to make sure that the boiler is adequately sized to provide enough heat to recover the cylinder in a sensible time. This will imply a certain flow rate and pipe size for the primary connections to the cylinder - normally 22mm.
Motorised valves are completely standard, so no design decision there.
If the boiler is not a system one and does not have an internal pump then in a proper design, one would normally work out the required flow and head in order to select the right pump type and setting. However, with electronically controlled pumps such as the Grundfos Alpha this is largely taken care of anyway.

No it isn't, but that is where most of the *design* work is - not in the boiler.

... and checking the provisioning of services, adequacy of plumbing and so on.

That depends on where it has to run

Agreed. I am simply pointing out that it may do and that can be difficult and expensive, which in turn may be a decision factor in what to do. It is better to point this out up front so that it can be checked, rather than glossing over and potentially having a nasty surprise.

Fine, but it should all be taken into account.

We have no data to say one way or the other.

.andy
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After I had hopes for you too, and you say that.

You are getting there. Or are you? It vastly reduces the design aspect too.

There is, especially for a novice.

It is easy enough, and about the only complex part in fitting a combi.

It is not a Middle East oil pipeline.
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Please explain precisely how it reduces the *design* NOT the implementation aspects.

This is a put down.
Please explain what is difficult about these aspects.

Do you have some exact design rules? Please quote an example and give the basis of calculation such that it can be adapted to different situations.

It might as well be if it involves ripping out the floor or wrecking the decorations of a kitchen.
.andy
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Nahhhhh. You are not getting there.

The whole is being ripped apart anyhow.
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Predictably, you have ducked the issue when put on the spot.......

You don't know that. .andy
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