Please help - to microbore or not...?

OK, I am so fed up with different plumbers and all their different opinions. Can any of you help?
I have a very simple question and I hope its a straight forward answer. I will miss out on the problem and suggested solutions and hope this can be answered without the details.
Q Would you be happy keeping 8mm microbore thoughout your house (with flow problems) or would you upgrade all to 15mm?
I realise that you may want more details but I'm not gonna give them. This is the most basic difference 3 plumbers have told me.
No. 1 wants to change all pipes to 15mm No. 2 wants to change only the 6mm pipe to 15mm No. 3 wants to keep the 8mm
Please help. Its doing my head in!
Many thanks Rebecca
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On 18 Aug 2003 00:19:23 -0700, reb snipped-for-privacy@hotmail.com (Rebecca) wrote:

I have 8mm pipe throughout my house, Rebecca, and there would be no need to change it.
The question can't be comprehensively answered without some level of background, and some detail of explanation is needed to make the right decision but I'll give you the following::
- Systems using microbore are not any different in principle to any other. The typical implementation difference is that systems using 22mm and then 15mm tube to radiators are connected like a tree with the 22mm forming the trunk and the 15mm the branches. In microbore installations it is typical to have one or more manifolds which are distribution points attached to the 22mm pipes and then 8mm (or sometimes 6mm or 10mm) are run from those to the radiators. In effect you might connect our or more radiators to a single point. There is no reason that manifolds have to be used, however - a microbore system could be designed like a tree.
- In any system, the amount of heat that can be delivered from a radiator is determined by its size and the room temperature (plus some other factors), but assumes that a certain flow rate of water is going through. The larger and higher output a radiator is, the more water flow is required. Tube of any kind has a restricting effect on the flow of water. The longer the length, and the smaller the diameter, the greater the restriction. To some extent, the pump makes up for this, but there is a limit and a properly designed system should have the flow speeds through all pipes under 1.5m/sec. Think of it like a stream which flows quickly and a river, with greater dimensions flowing more slowly.
- You can relate the pipe diameters as a result, to the amount of heat. In a proper design, the heating engineer will have worked out the pipe sizes based on the amount of heat required to be delivered through them - there are tables to do this. However, as a rule of thumb, 15mm tube in an average house can carry up to 6kW of heat and 8mm up to about 2.5kW. 6mm is about 1.5kW. These numbers are reduced if the lengths are overly great. In the case of microbore and radiators connected to a manifold, each can be considered separately and you can work out immediately whether pipework is adequate. In the case of 15mm connected as a tree with more than one radiator on a run of it, you add the requirements of the radiators.
- You can work out radiator heat outputs by measuring them and looking up the manufacturer's data sheets. The nominal output in the tables, which comes from a European measuring standard needs to be scaled downwards by multiplying by 0.9 for most UK heating systems.
- In a practical case where you already have a system, it may be working perfectly well. If it isn't, the usual problem is that one or more radiators are not getting hot enough or at all. There can be three causes of this:-
a) The system wasn't designed properly and there are one or more radiators that are too large for the size of pipe. The only fix for this is to put in larger pipes or to reduce the radiator size, perhaps adding a second radiator connected back to a manifold.
b) The system isn't properly balanced. This procedure involves adjusting the lockshield valves on the radiators (these are the ones at the opposite end to the ones you turn) so that the flow of water through each radiator is adjusted to what is required by it. Doing this properly is time consuming and requires a thermometer to measure the temperature at each end of a radiator. You then go round the house adjusting a little at a time until the correct temperature drop of 12 degrees C is measured at each radiator. The problem is that adjusting each affects the others so this can take a very long time. Hence CH installers often take a short cut and just adjust the hottest radiators down until the coolest ones warm up.
c) The system has become silted. This happens from the corrosion of steel radiators and produces a brown-black sludge. In a microbore system, this can tend to reduce the flow through the pipework more quickly than 15mm because some is carried from the radiators into the pipes. The smaller size of microbore will obviously silt up more quickly. However, the problem is entirely curable by flushing the system with clean water. In a badly silted system, it's helpful to take the radiators off and flush them outside. This does require care to avoid silted water, which is a great brown dye from dripping on the carpets. Another favourite game of plumbers is power flushing to do this task. They connect up a powerful pump and some cleaning chemical to do it and charge several hundred pounds. This is a rip off considering what is involved. The whole situation of silting is very easily preventable by the addition of corrosion inhibitor (about 20 every three years) to the system. I've done this in my system (18 years old) since new and it has remained virtually pristine.
I can see no reason at all to change everything to 15mm unless the system was so badly designed that all the radiators are inadequately connected. I think that plumber (1) is just looking to expand the work and the the price. It wouldn't be British Gas would it?
There may be some merit in changing 6mm pipes if the radiators using them are not warming up, provided that balancing and silting have been eliminated.
If everything is properly designed, clean and balanced there should be no reason to change from 8mm.
.andy
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I live an old house (17th C.) so installed microbore over 25 years ago. I've had no problems in all that time. I think it was 8mm and am not familiar with 6mm.
If it aint broke don't mess with it!
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Very useful information Andy. Thanks.
I wonder if a bit more info will narrow it down then...
Our house has a mixture of new and old steel rads. The new ones are fine (not as hot as they could be but they heat up more or less evenly), but the steel rads are heating very badly (only the top 2 inches)- despite us removing them last year and cleaning them thoroughly (and cleaning the system with Fernox etc).
So, we were recommended to buy new rads to replace these old ones, which we have done - I must admit the plumber who told us the sizes to buy did guestimate. Looking at the B&G catalogue, the output of these 4 new rads ranges from 4500 to 6200. 3 of them are currently on 8mm, and the smallest is on 6mm.
From your figures Andy if the general rule of thumb applies, it looks like we will have to replace most of the pipes (as 8mm generally deals with up to 4500w). Have I interpreted this correct?
The plumber that recommended changing all the pipes to 15mm (but did not recommend changing the rads) was the only one which was recommended to us.
Your opinion with this extra bit of info would be much appreciated!
Changing tac slightly 0 another plumber told us that we would have to change the pipes coming form the boiler (some sort of Potterton) from 22mm to 28mm and that is why the circulation is bad. This sounds dodgy to me...we had about 6 plumbers round and no-one mentioned this. What do you think?
Thanks Rebecca
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Have you added rads, or have you just replaced defective rads. If just replacing then did the system operate fine previously. If it did work fine then you have blockage of some sort.
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Hi Andt,
To answer your queries:
1. The rads I mention are not as old as the antique types you mention so I guess I mean old versions of more modern panel types.
2. I thought it was the typical triangle shape heat distribution but it also sounds a bit like the top only and either end of rad heating you suggested (I get the impression I am, not beong clear!)- when we cleaned one out last year, it worked perfectly for a couple of weeks before going back to the orignal useless heat distribution.
3. Yes, the new rads are in BTU/hr so I guess the existing pipes should be ok. Phew.
I think we'll get a bloke round to change the rads and see how we get on then. Fingers crossed it will be fine!
Thanks for the tips. You don't live near J9 of the M25 by any chance do you? You sound like a very useful man to know!
Will keep you updated Rebecca

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On 20 Aug 2003 10:41:40 -0700, reb snipped-for-privacy@hotmail.com (Rebecca) wrote:

Hmm. Then I think that considering you have had Fernox in the system it is not likely to be corrosion of the radiators themeselves, at least certainly not in that timescale.
Silt and crud somewhere being carried into the microbore pipes from another radiator or pipework that does have some sludge is plausible if the system went bad after a while - especially if the 6mm is worse or became worse more quickly than the 8mm.
Do you have thermostatic valves or was anything else changed?

Hopefully, although I am not sure.
You could usefully ask him to flush the system at each radiator valve (both ends) as he goes to see if it brings out any grot from the system pipework.
If there is, then it would be worth going to each radiator - even those which are apparently OK. Take them off and outside and flush them through with a mains water hose or a pressure washer if you have it. Flush from each radiator valve as you go to carry any silt in the pipework out. Unfortunately just flushing to a drain cock in one place doesn't really achieve this well.
This sounds like a bit of a pain, but you can actually do a whole house worth of radiators in a couple of hours. Do note the settings of each lockshield valve if you close it at all. Having said that, I have a feeling that a balancing exercise is going to be on the list as well.
Also another reminder - do watch for the sludge and even rusty water drips. The compounds are one of the most indellible dyes known to man :-( One useful trick if you are taking radiators outside is to put a small plastic sandwich bag over each tail after you have undone the nut and attach with a rubber band. Then you won't get drips on the floor. I also found that new cat litter trays from the supermarket are a cheap and useful container to put under the valves as you undo them and even to flush.

My "world of adventures" is nearer to J10 of the M4 :-)

Please do - this is a bit of a puzzle.

.andy
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And get a powerflush on "all" pipes. Then run the system on 80C all the time. If you are getting new rads get low surface temperature rads as these can be safely run at 80C.
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For this it is worth shopping around. BG charge outrageous prices. It is also possible to hire the equipment and chemicals.

touch it.

.andy
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You can touch LST rads, which is also good for children.
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wrote:

But cabinets look naff
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.andy
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wrote:

Have you seen the designer rads these days?
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Yes. I think that the futuristic looking ones look especially hideous.
I did take a look at a Myson product that had a wooden bench across the top that I was considering for the conservatory at one point.
The trouble was that it was over 1600 exc. discounted.

.andy
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wrote:

The whole non-condensing heating system is designed to run at this temp. Even some condensing boilers designed to maintain an old 80C system, in that it will run it 80C if it needs to. Since 1980 Sweden and Denmark have standardised on a 60C max rad temp.
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Andy Hall wrote:


Quote today to replace a balanced flue combi with a new Valliant fan-flued combi + make good ship lap boards on the outside. Me 1500. BG 2532. (I thought they would be around 2250).
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Rebecca wrote:

I think that unless the boiler is rated at 35kW or more then the 22mm pipe will be fine.
Over all it sound as if they system needs rebalancing and the 6mm pipe upgrading (becasue the slightest debris would have a really big effect on it, I guess it is perhaps only 1/3 the area of the 8mm pipe _internally_.
The guy that wants to do all 15mm is likely being over cautious - the system nearly works.
I'd probably choose to upgrade the 6mm pipe to 8 or 15 (depending on the layout), leave everything else as is and then spend time rebalancing the system to get the 'old' rads to heat up (the water is taking the easy route thru the 15mm new stuff).
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I would leave the pipes alone, as they worked fine at one time. They obviously need cleaning, so cleaning is a priority. I would also put a strainer on the return to the boiler to collect any debris in the system which will save the boiler and pipes. Then balance.
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