One Pipe System Central Heating

[KM1]

Just moving into the ground floor apartment of a 7 storey building. The building has a central one pipe heating system. We needed to move one radiator but the problem is that it no longer heats up. The pipe going in is hot but the one leaving the radiator is cold. The radiator, valves etc are all fine. The building plumber tells me that whenever residents move the radiator and extend the pipes / introduce right angles into the pipes, the radiators stop working. Isn’t that strange? We were told this prior to moving the radiator .... and it turns out that he was right. Why isn’t the hot water flowing through the radiator? We’ve confirmed that there are no air pockets, valves work, radiator works. Just doesn’t heat up enough once we put it into the new configuration (with extended pipes and some new 90 degree turns in the pipes). Very perplexed!

 

[KM1]

It’s a 100 year old building. Could the fluid pressure be low? Are there in-line pumps available that could force the hot water to flow through the radiator?

Any other solutions?

 

[muggles]

You've created additional resistance in the pipework which is stopping the flow, I suspect. Can you post some photos? Upgrading the pipework a size may help, as may changing the configuration to TBOE on the radiator. No, you can't pump it, you'll ruin the entire system trying to do that

 

[stem]

It's simple physics. With a one pipe system, the water is pumped around the one pipe loop, meaning that because the radiator inlet and outlet pipes are connected to the same pipe they receive the same pressure from the pump, as a result, the pump can't force the water through the radiator in the same way a two pipe system does.

One pipe systems rely on the gravity principle of hot water rising and cooler water sinking to circulate through the radiator. This means to work the radiator ideally should sit directly atop the one pipe. The one pipe can of course be re-routed so that it passes directly below the new radiator.

If there is a slight horizontal distance away from the one pipe, (ie it's not directly above) through a wall for example, the pipe must be inclined upwards and the horizontal distance kept as short as possible.

What you can't do is have the two radiator pipes from the 'one pipe loop' running horizontally and through bends before reaching the radiator because the pump pressure on the flow and return pipes is the same it isn't able to force the water through the radiator.

If you re-route the one pipe loop so that it passes directly below the radiator, with the pipes going directly vertically in and out of the radiator above, all will be well.

 

[cross thread]

In addition to the previous advice some new radiators and valves are not suitable for a one pipe system

 

[KM1]

Thanks everyone. A few clarifications - the hot water pipe is vertical and we can’t really change that. I’ve sketched the original radiator (in red) and the new piping and radiator (in green). The new piping and radiator does not work. Any ideas on how to connect the new radiator (upper valve / lower valve? Connected to which pipe upper or lower?)

please advise what combination might work .... as of now we are connecting 1 to A and 2 to B. Is there a different permutation that might work better? Please see attached diagram. I’ll upload photos too by tomorrow.

also what radiators and valve companies work with single piping system?

thank you!

 

[Nige F]

That dropping down and then going back up ( whatever the pipe size) is stopping circulation

 

[stem]

As @Nige F, the pump pressure on the radiator inlet and outlet pipes will be the same, so there is no pressure available from the pump to help push the water around bends and loops. The existing radiator installation method is what you would need to replicate. The radiator should be located as close as possible to the vertical one pipe, with direct horizontal connections without "dropping down and going back".

If the radiator needs to be further away from the 'one pipe' then a loop in the 'one pipe' can be installed to keep it close to the radiator.

Although this would become difficult because of the existing radiator on the other side which would also need to remain close to the 'one pipe'.

 

[dilalio]

Us plumbers are clever in that we can circulate water without a pump and therefore electricity!

 

[stem]

Although this would become difficult because of the existing radiator on the other side which would also need to remain close to the 'one pipe'.

There you go! how about this:

The 'one pipe' loop would need to be the same diameter as the existing pipe. It would be a good idea to get a plumber who has worked on one pipe systems to do the work, I'm assuming the install you have just had done was DIY and not done by a professional plumber.

 

[stem]

Just wondering how you got on, everything working now?

 

[Agile]

Reading this thread I also wonder what he did.

Looking at his sketches, it would be easy to assume that it might work if the connection pipes were made totally horizontal.

In practice it might work a little but the extra flow resistance will probably much reduce the flow through it.

One pipe systems can work very well but they have their limitations and need to be carefully designed.