adding a radiator to combi system

[jmh474]

first off just like to say hello as this is my first post.
so im looking for advice about central heating, i want to add a extra radiator to a combi system, the main pipe is in 22mm and the rads are fed in 15mm, my question is can i come off the 15mm or do i have to come off the main 22mm which is alot more work.
if its all right to come off the 15mm the run would be from an up stairs radiator to pipe straight down to down stairs and through a brick wall to a new 4ft radiator, or do i have to come off the 22mm??
[/u]

 

[Whitespirit66]

If the 15mm only feeds one rad at present, should be OK to come off of that. Very general rule of thumb is that 15mm pipe can handle 15,000 BTUs (approx. 4.5 Kw).

 

[jmh474]

yeah its only feeding a single 4ft radiator and its about 3m away from the 22mm pipe