central heating - flow & return circuit design

Apologies if this is a daft question. Hope the ASCII art works!
Is there any reason not to 'spur' feeds to radiators, thus
BOILER * # * # * # RAD ***** # ######## * # ******* RAD * #### * # * # BOILER
The spurs might be 3 or 4 meters from the main feed in the design I'm considering.
Or is it better to have the radiators in a loop, thus
BOILER * # * # * # RAD * # * # * # * # RAD * # * # BOILER
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

No. It is the usual design.
Your ASCII art shows two boilers, however, which could be far more problematic!
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Christian McArdle wrote:

Yeah. That's cos my ASCII art wasn't up to looping back round. It was a logical design! It was having such long spurs I was worried about. I've usually seen the spurs as only a few inches of 15mm pipe from a 22mm loop.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Use whatever is convenient. Sometimes it is convenient to snake a main run around the radiators. Other times it is convenient to run long spurs to them. Sit down with a piece of paper and work out which is best for you. If you are installing yourself, put insulation on the long spurs, or you'll spend your money heating the cavities where the pipes run before you get round to heating the rooms!
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Use a sealed system with microbore and manifolds. Less problems.
Just to add:
Plumbing Mechanical Service Book 2, a NVQ plumbing book. This is not a DIY book so please don't buy. It has a section on heating, and a sub section on Mini-bore on page 170. It says:
"If the manifolds can be situated in such a way that the branch flow and return to each radiator is approximately the same length, the frictional resistance will also be approx the same, making the system self balancing".
And on page 171:
"In a well-designed system balancing should not be necessary as the aim is to keep all pipe runs to heat emitters at, or near, as possible, the same lengths."
And on page 172, there is a cut-away of a twin entry rad valve without lockshield adjustment because in properly designed mini-bore systems, which is easy to do, balancing is not required.
--
--

Checked by AVG anti-virus system (http://www.grisoft.com ).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Certainly have. However, O-level physics is all that's required to see this is complete garbage. (I don't know if today's GCSE would cover things like continuous flow calorimeters and basic fluid dynamics, but O-level did in my day.)

Try reading it again, particularly the bit you just cut.

In which case you don't understand what balancing is. I suggest you find a better textbook to learn about it.

I was finding it hard to believe an NVQ course book would be so wrong, but on the other hand, it might go some way to explaining the garbage I've heard some heating engineers spurting out. Still wondering if you are just quoting it grossly out of context, but I can't see any circumstance where what you quoted would be useful -- it's only correct if all the radiators are identical and are expected to produce same heat output which is unlikely to be a real life requirement. The only scenario I can imagine would be something like a large room with several identical radiators and a flow and return manifold dedicated to that room.
--
Andrew Gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Only from your postings......
.andy
To email, substitute .nospam with .gl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

This is a bit unclear, Rob. I assume you don't mean that you have two boilers.
For most houses, the main trunk pipes from the boiler will be 22 or 28mm.
It's quite normal to spur from these to radiators, but you do need to watch out for the flow rates required by the radiators.
To avoid noise and problems with insufficient flow, it is normal to design such that the rate through a given pipe section does not exceed 1.5m/sec. Since the heat that can be transferred to radiators is directly related to flow rate, it is possible to work out pipe sizing required for given capacities of radiator.
You can use a very rough rule of thumb method for this whereby for lengths of a few metres, 15mm pipe will transport 6kW of heat and so on, or you can work it out properly. Since the exercise is pretty easy, I would recommend the latter. There is a step by step guide by the Copper Development Association on how to do it.
http://www.cda.org.uk/Megab2/build/Pub150%20UKCB.pdf
Basically you need to make sure that the heat carried over given lengths of pipe is within their capacity, accounting for fittings and bends.
Generally, it is going to be preferable and easier to spur from your main trunk in 15 or if need be 22mm tube, rather than having long trunks, but it is not critical as long as you stick to the rules.
Just to be 100% clear, though, in either case you connect the radiators across flow and return, you don't connect them in series with a single pipe. Sorry if that's stating the obvious.
.andy
To email, substitute .nospam with .gl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Andy Hall wrote:

Very helpful thanks. I was intending to spur in 15mm from 22mm trunk. The radiators on the spurs are tiny now I've insulated my walls, all under 1kW, but I'll have a good read through the pipe guide.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 28 Aug 2003 11:06:38 +0100, "Christian McArdle"

8mm microbore is suitable for up to 2500W on the rule of thumb basis.
I have it run from manifolds on the 22mm trunks at a number of positions in the house and the microbore runs are anything up to 6m to the radiators. The outlets can be made quite neat. At least one manufacturer makes an electrical outlet plate with hole at the centre for the pipe. The microbore pipe is run beneath the plaster to a flush outlet box at each end of the radiator where a swept elbow is then fitted. A tail of tube bent gently with a pipe bender then connects to the radiator valve.
It's also somewhat easier to run under floors than hard 15mm pipe and through joist holes even if they are not perfectly aligned.
I've never had any silting problems, only some of the original swarf that should have been flushed out by the original plumber and wasn't. As long as corrosion inhibitor is used and maintained as specified, there is no reason for silting to happen on any system.
I have a couple of radiators of 3kW and 4kW and it isn't suitable for feeding them, but apart from that, I would and have used 8mm tube on new installations.
.andy
To email, substitute .nospam with .gl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

A standard radiator system is fed from pipework of a required internal diameter to suit the load required to heat the property. The radiators are not fed in a loop configuration, but are actually fed individually from the flow and return pipes from the boiler. If radiators are connected in a loop type system, then the heat lost from the first radiator is cooling the water down so much that the next radiator in the loop will not heat as much as the first, the next along in the loop would be getting water that has already lost even more heat, so would hardly heat up at all.
Can you tell us what type of house you're putting this installation in and what plumbing experience you have ?
--
www.basecuritysystems.no-ip.com
Outgoing mail is certified Virus Free.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
BigWallop wrote:

Sorry. This was me not being clear. I realise the radiators don't connect in a loop, unless in a single pipe system?, rather that installations and schematics I have seen have effectively looped the main feed and return around a floor and used relatively short spurs, rather than using a "spine and rib" kind of design that would give me shorter pipe runs.

A 150 yr old 2 bedroom detached house with small, sparsely spaced, single glazed windows. This is the first complete central heating system I've installed, but I've replaced and/or added bathrooms, radiators, pumped drinking water supplies in the past. None of which have flooded their respective houses yet!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Then I think you will have a fairly good idea about most of the practical plumbing issues.
I would recommend purchasing the Domestic Heating Design Guide from the Heating and Ventilating Contractors Association (19.50 from www.hvca.org.uk)
This collects together in one place all the information that you need to do the pipework calculations that I mentioned, the heat loss and radiator sizing calculations, derating, design info for sealed system components, etc. etc. It isn't a how to do plumbing book, but I don't think you need that. I found it a convenient source of all data and method that I needed. A few other group regulars have bought it and found it similarly useful.
.andy
To email, substitute .nospam with .gl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

This book is sadly lacking.
--
--

Checked by AVG anti-virus system (http://www.grisoft.com ).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

course entitled to your view, but you would appear, as usual, to be in a minority of one.
.andy
To email, substitute .nospam with .gl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Except that you are not.
.andy
To email, substitute .nospam with .gl
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

ROFL. OH my God, snotty wit!
--
--

Checked by AVG anti-virus system (http://www.grisoft.com ).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
BigWallop wrote:

All the walls are, or will be insulated with 40mm phenolic foam backed plasterboard. I personally think you lose a lot of heat through solid stone walls, or at least the absorb a lot and dissipate it too slowly to be of much use. The U values are abysmal compared to modern construction. They can offset this a little by acting as a thermal store, but I tend only to be sitting down and feeling the cold for a couple of hours a day in the winter, and so have the heating on, so for me this never really happens.
The windows are small by any modern standards. The 5m x 3m x 2.6m "living room" has 2 1m X 1m single glazed windows. Purely in terms of heat loss I don't think double glazing will make much difference. Cold air currents may be an issue, but I'm hoping the traditional radiator under a window method will offset most of that.
Thanks everyone for the advice, confirmation and amusing spat.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Good luck with Rob. I see you know what to look for so I know you will be OK in tackling this job.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.