Hot water feed from cylinder

[Hellfire]

I've been advised that there is a minimum horizontal length, that the hot water feed from the cylinder needs to be before tee-ing into the vent/expansion pipe. Can anyone advise what this minimum length is?

I've fitted a Salamander flange to the HW cylinder and need to re-plumb the hot water take off pipe. I'd like to take the shortest/easiest route directly to the vent/expansion pipe but am concerned this may cause problems if it's shorter than the recommended length.

Any advice would be greatly appreciated.

 

[buffy27]

475mm minimum.

 

[plumbbobshan]

Only 450mm min when i went to school. But saying that i have had it shorter in a tight airing cub , and no probems !

 

[Hellfire]

If I take the most direct route, the horizontal length would be about 300mm, about 2/3rds of the recommended length. What problems would it likely cause if it were too short? Does anyone know why it is recommended at 450mm?

 

[pnhsolutions]

450mm mate!

 

[justlead1]

Hi. Parasitic circulation ( the ability of hot water to set up circulation currents in a single pipe) resulting in heat loss of the stored hot water. The 450/470 mm horizontal length provides sufficient friction to stop this gravity circulation. But please consider, with a 36" x 18" cylinder and a cupboard with just enough room to fit, how did the rest of the country comply, they did not all put a 90 degree bend in to achieve the criteria. Good Luck

 

[buffy27]

450mm mate![/quote]
i am officially religated to the second best plumber on the forum.
thanks alot mate.
watch your back , i will be back on top again.[450mm not 475m]

 

[stevetheplumber]

450mm mate![/quote]
i am officially religated to the second best plumber on the forum.
thanks alot mate.
watch your back , i will be back on top again.[450mm not 475m]

surley the 450 is a maximum length of straight pipe its the bend in the pipe that stops the parasitic circulation its not realy much of a problem with temperature controlled hot water it realy harks back to the days of coal fired back boilers and cold houses
cooling at the edge of the pipes caused a ciculation in the vent pipe