Single Pipe Central Heating System with 2 loops

23 Apr 2006
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United Kingdom
The kitchen in my house doesn't have a radiator and gets freezing in the winter. The huge living room radiator (2m long no fins) also struggles to heat up. My intention was to add a new radiator in the kitchen, and replace the living room rad with one with a higher BTU for a smaller footprint.

Then realised I have a single pipe system (all rads have bypass pipes underneath) .......

I am currently sketching out how I may be able to run a new feed and return system, without tearing too much of the house up.

In the process of this planning I have come across some oddities with my existing circuit.

From the Boiler a 22mm Feed tees off to :
1) a 15mm pipe run that feeds the main bedroom upstairs then drops downstairs to feed the living room and hallway. It then disappears under laminate flooring in the dining room.......

2) a 22mm pipe that runs through the 2nd bedroom, bathroom and 3rd bedroom before looping back to the 2nd bedroom where it drops down into my dining room, where it feeds a radiator then disappears under laminate flooring.......

Returning to the Boiler is a 22mm return pipe that rises from the dining room downstairs (hidden in boxed in extension to chimney)

I am assuming that both the 22mm circuit and the 15mm circuit meet somewhere near my chimney in the dining room and return on the single 22mm return.

Was this a conventional method of extending a single pipe system?!
It appears to me what this does is prioritise the upstairs radiators first before the 2 loops drop downstairs. Which is why its ruddy cold downstairs!

Would you all strip out and replace, or modifiy the existing circuit?

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Sounds like your system may need balancing if it's too hot upstairs and cold downstairs (see the FAQs for how to do this). If it's chilly in most places then it may be that either your system is sludged up or your boiler is undersized, in which case adding an extra rad won't help a great deal. Check the balancing before doing anything else
It sounds as if you may have a combination of single pipe and parallel systems.

Or more likely two single pipe systems.

Either way balancing may not be possible or only possible to some extent.

As you seem to have covered most of your pipework then any modifications may be difficult.

If you want to maximise the disruption and work then repipe the system as a parallel system.

If you want to minimise the disruption then add new rads as required but piped as a parallel connection back to the boiler. Dont forget the integrity of the loop needs to be maintained.


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