Radiator layout question....


Postby BrokenMan » Sun Oct 04, 2009 4:23 pm

Hello everyone!

I am having a problem in understanding the best way to lay out my central heating system so that all the radiators will heat up correctly. I have checked numerous books, schematics and posts on various forums and they all seem to either be different or miss out the detail I am looking for! I apologise in advance if I don't use the the correct terms but I'm sure you have guessed I'm not a GCH engineer!

I have a gas combi boiler which has a separate hot water and dual pipe central heating circuit (Feed and return for one circuit of central heating). I intend to plumb in the radiators in parallel to each other off of a manifold as is depicted in this [url=http://www.diydoctor.org.uk/projects/centralheatingsystems.htm]double pipe system.[/url] There will be an upstairs loop and a downstairs loop which will be split from the boiler for the feed (hot in) and the return (hot out).

My question is how do I plumb in the FINAL radiator in EACH loop of my circuit? Series or parallel? Do I plumb them like in the picture from the above link where the final rad is part of the circuit or with the loop continuing to join the feed and return lines?

Some schematics show the final radiator in series, the hot water flows in to the rad and then the hot water out of the rad goes to the return line. If you do this will you not choke the return of hot water to the boiler? Other schematics show the final rad in parallel so that hot water in goes to the rad and the loop continues round where it joins the hot water out from the same rad and then the loop becomes the hot return to the boiler.

To me the second option of having the final rad in parallel like all the rest makes sense so that if you close the radiator off, it doesn't choke the return of the water to the boiler. Then again, if the feed and return lines are joined together in a loop will the rads all heat up efficiently?

Any advice or links to a good schematic / picture will be GREATLY appreciated!!
edit-----
link should be http://www.diydoctor.org.uk/projects/ce ... ystems.htm
Last edited by BrokenMan on Tue Oct 06, 2009 8:03 am, edited 1 time in total.
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Postby twgas » Sun Oct 04, 2009 7:11 pm

Link didn't work, you'll want 22mm main flow and return with 15mm to individual rads, will try a diagram shortly.
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Postby plumbbob » Mon Oct 05, 2009 8:11 am

There is so much that worries me about this post, I don't know where to start. As twgas says, your link doesn't work.

Radiators can only be installed in parallel - each having one end connected to the main flow pipe, and the other end to the return pipe as in the lower diagram of

http://www.diydoctor.org.uk/projects/ce ... ystems.htm.

If the rads are linked in series, turning one off would switch all the others off too, or have we lost something between your description and my understanding?

I am confused about "from the boiler for the feed (hot in) and the return (hot out)" - surely it is feed(hot out) and return (cold in)???

Why a manifold?? Are you using microbore (10mm pipe)?

"If you do this will you not choke the return of hot water to the boiler? Other schematics show the final rad in parallel so that hot water in goes to the rad and the loop continues round where it joins the hot water out from the same rad and then the loop becomes the hot return to the boiler"

Sorry but you have just lost me there!

The only way to design a system is as in the second diagram of the link I posted. All radiators bar one must have thermostatic valves fitted. The remaining rad situated in the same room as the thermostat, has two lockshields which will guarantee a flow of water. Each of your two circuits must have one of these.
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Postby DEEARR2 » Mon Oct 05, 2009 6:59 pm

Connect all your radiators in parallel so that each rad will take what it requires from the system. Most modern combies are fitted with auto by-pass facilities that operates in the event of all trvs closing.
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Postby BrokenMan » Tue Oct 06, 2009 8:23 am

Thanks so much for the replies and plumbbob I am sorry for worrying you. Unfortunately the link you provided comes up as not found. I will try to explain and clarify myself.

I understand using 22mm pipe from the boiler hot out to cold in, (I used the term hot out for return sorry.) with 15mm tees for each rad. I understand using TRV's on the rads.

By manifold I was using a generic term for a main supply ie the run of 22mm pipe which all the rads tee off of. I am not using a microbore system.

"If you do this will you not choke the return of hot water to the boiler? Other schematics show the final rad in parallel so that hot water in goes to the rad and the loop continues round where it joins the hot water out from the same rad and then the loop becomes the hot return to the boiler"

Sorry but you have just lost me there!.

I should have said:

"If you do this will you not choke the return of hot water to the boiler? Other schematics show the final rad in parallel so that hot water in goes to the rad and the loop continues round where it joins the cold water out from the same rad and then the loop becomes the cold return to the boiler"

If you click the link at the bottom of my post you should see what I mean.
In the picture of a double pipe system, the first two rads are in parallel, the last is not. The main run (I'm not calling it a manifold now) of hot from the boiler goes to the rad, comes out of the rad and becomes cold out which goes back to the boiler. This is series, not parallel.

If the rad was in parallel, then the final rad will tee off the main run like all the other radiators but the hot out and the cold in from the boiler must have to join together to create a loop.

Plumbob is that what you meant by having the final rad with two lockshields so that flow is always on? This final rad will be in series but will always be on?
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Postby plumbbob » Tue Oct 06, 2009 4:56 pm

Well Brokenman, as far as I can see, your link is exactly the same as mine, and if it is, how come yours works and mine says error??????

To my eyes, in the diagram all three radiators are plumbed the same, ie in parallel. The fact that one rad is at the end of the run is not relevant. Maybe because it is at the end of the flow and return, it looks different, but it isn't. Honest.

In fact, few systems are as simple as the diagram, in reality, there could be branches off at any point for flow and returns to different areas of the house. You don't need a continual run from one rad to the next, to the next and so on. As long as each rad has a feed from the flow and a return to the return side, all in the correct size pipe will do just fine.

If every rad in the system were to be turned off, (I'll ignoring bypasses) then indeed the flow would be choked, in fact stopped totally. This is not acceptable so as I say one rad, usually in the hall, is left with tamperproof valves to ensure this cannot happen.
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