Additional Radiator: 10 or 15mm?

[KitchenTim]

Hi All,

Could do with a bit of advice, I've got one of those jobs I'd rather not have to do I have to fit a radiator in a dining room extension, sized by heat loss calculation a 1200W rad is going in with TRV.

The house is 15 years old and has an open-vented system with Y-plan valve and 10mm copper to individual rads. My usual experience with these systems, though common, is that they seem to be designed to trap air and can be a real pain to re-fill.

The new rad will be about 8m pipe run from an existing one, but I guess it would not be wise to tee off below the valves on that one and run two large radiators from one pair of 10mm flow/return branches?

If this isn't an option, I will find the main 22mm flow & return pipes and tee off them. This will probably result in the pipe length being about 12m on each of flow & return from the 22mm tee to the new rad. Can anyone confirm what the maximum run in 10mm is? Am I best just running it all in 15mm copper?

Any help gratefully received.

Cheers, Tim.

1200 w is only a 600 x 700 double rad.
not knowing what size the other rad is hard to tell but if it the only rad on the 10mm pipework from the flow/return it shouldn't be a problem teeing off that.

[KitchenTim]

Thanks AJS, I think the other rad is a similar size/output, so hopefully we will be OK. That'll make life a whole lot easier :-)