mixing 10mm & 15mm

[AJ16]

Is is ok to go from 15mm to 10mm bore then 15 again when connecting to one small bedroom rad? The feed & return pipes across the landing are 15mm, spur feeds are needed from these to a new rad in the bedroom. There are 2 steps up from the landing to the bedroom, there are existing unused 15mm pipes running from the top of the steps and a short way under the bedroom floor boards, they need connecting to the F&R & extending under the floor to near the rad probably with plastic/pushfit, the final connections from under the floor will be by 10mm as it's easier to conceal. Would it be ok to run the spurs as 10mm as they need a few turns to negotiate under the steps & 15mm is a bit lumpy?

I can add a diagram, just not sure how to attach..

 

[stevetheplumber]

yes shouldnt be a problem provided the rad isnt a two metre double

 

[AJ16]

No it's just a 600w x 700h Stelrad K1

 

[lame plumber]

pointless going back upto 15mm once you restrict the flow.

 

[Leo21]

pointless going back upto 15mm once you restrict the flow.

What he said.

 

[Simon F]

there will likely be more resistance to flow on this new pipework than the rest of the system, so be prepared to need to balance out the rest of the system to get heat into this new radiator.

 

[AJ16]

pointless going back upto 15mm once you restrict the flow.

Thanks, I understand what you are saying, but the 15mm section is already in place although only around 900mm long. The total length of the spur to the rad would be around d 4.5m. Does thai make a difference?

 

[AJ16]

there will likely be more resistance to flow on this new pipework than the rest of the system, so be prepared to need to balance out the rest of the system to get heat into this new radiator.

Thanks, there are already several 10mm runs to other rads, they work ok, understood re the balancing. It's just that I'm trying to work out if I might be better off either trying to run the whole thing as 15mm (tight for space), or rip out the short 15mm section and run it all as 10mm??

 

[Leo21]

If possible I'd run it in 15mm, don't forget it's 4.5 metres times 2. It's got to go there and back.

 

[Best]

I never have came across anywhere I can't run 15mm to rads. A few I must admit would have been a lot easier & saved time if done in 10mm, but it is really just down to making more effort.
That all said, since other rads are done off 10mm then you won't be doing any harm