1 pipe system

[jaydebruyne]

Taken on a job - woman's house is part flow/return 2 pipe and part 1 pipe system..

I'm ripping out the remaining 1 pipe and joining into the existing flow/return.

Other than new valves if they're still the ones for 1 pipe systems, it no different to piping up a normal flow/return system is it?

It's on a combi boiler system.

Is there anything I need to be aware of as I've never worked on a 1 pipe system before. I understand how it works in theory but just wanted to check if I needed to be aware of anything when changing it over to 2 pipes

 

[Chalked]

Watch out for bathroom rad off gravity hot water.

 

[jaydebruyne]

The recently added section of flow/return was put in in 15mm - is there any point in going to 22 after this? I was thinking of running the rest in 15 also..?? It's not a massive place, maybe 8-10 rads in total, half house in 1 pipe the other in two

 

[newcastle phill]

Well work out the heat loading of the rads and calculate if 15mm can carry enough heat to make them perform as expected.
15mm can only convey so many Kw - just make sure its enough

 

[Best]

Old school way for 15mm pipes (on an open vented system) is 20,000 btus - close to 6kw. I still see that as correct.
That's really two fairly large double radiators maximum, or 4 or 5 fairly small rads, to think in simple terms.
Obviously a sealed system, like on a combi, is more capable but personally I wouldn't do too much 15mm in main flow and returns on any type of system. Got to also consider length of any long runs.
I prefer 22mm doing most of a main run right to the last couple of rads. It keeps the system easy to balance, as the end part of a circuit is always the hardest to heat properly and reducing the pipes diameter there would make it worse. I have always thought it sensible to maintain the larger diameter throughout the circuits main flow & return.

Also, - Don't forget that many modern designer rads require good flow to them, due to thin restrictive waterways.

 

[Last Plumber]

I agree with Best. Couldn't have put it better myself !