Changing a radiator with an 8mm feed

[jonnybegood]

Hi Guys
In the kitchen we have 1 double 400x600 convector radiator that does not sufficiently heat up our 20 x 12 kitchen.
So I have gone out and bought a 400x1800 designer type that gives off approx 400watts more heat.

The convector radiators flow and return are 8mm copper pipe that go up behind the kitchen units (approx 2 metres and then connect to a 22mm pipe.

There has never been a problem with the radiator, never needs to be bled, always good heat across all fins.

Now that i am fitting a bigger radiator that will be vertical up the wall can you see the 8mm pipe causing a problem apart from trying to get the correct type of valves.

I don't really want to replace with 15mm pipe because it will mean quite a big of extra work removing worktops and cupboards to get at the pipe and 15mm is not going to be so easy to bend behind the units and around to where the radiator is sited.

The new radiator will be 1200 watts, what problems are my likely to face in future from not changing the pipework.

Thanks in advance

JBG


Forgot to add that except for 2 other very small radiators (Airing cupboard and cloakroom) the rest of the house is supplied by 15mm pipes

 

[cider]

think your problem may be trying to heat that area of one 8mm circuit

 

[kevplumb]

The new radiator will be 1200 watts

it might be in the book methinks same as cider

 

[roberta1000]

Not a CH engineer but you say that your 8mm runs are about 2m long. I have a 2m x 600 double radiator fed in 8mm more than double this distance with no problems heating throughout its length so IMHO you will be fine as long as your pumping pressure is good (I run my pump at full speed).

Even at full whack though I don't think that 1200watts is really enough for a 20x12 room. (2d worth).