Radiator valve drain valve locations and number

[Barnman]

Where abouts should drain valves be put on the central heating system - i.e. on what radiators. I assume the lowest point or the ones furthest away and if there is more than one ring then on each ring. The lowest point is under floor but I imagine most of the water would be sucked out by pressure. The towel rails are all higher up than the radiators so I assume they don't need one.
Are there building regs about this?

Thanks

 

[craig51]

Usually in a house a wee pipe sticks out the wall at ankle height which can be opened to drain the system.

In a flat, its usually on a radiator somewhere.

 

[Barnman]

I am putting radiators into a house i am doing up so just want to make sure I do it correctly.

 

[craig51]

T off from under the floor and stick it outside. Job done. You can if you have loads of time and cash stick one on every rad, but then you are potentially creating 10 extra leak points.

 

[JimCrow]

.

Ideally there should be two, one on each the flow and return so both pipes can be drained down,
if only one draincock is fitted the other pipe will be full of water up to the bottom of the lowest radiator.
.