Fitting radiator 22mm or 15mm in the run?

[happyhero]

Hi Can anybody advise me I am an ex-building services man and qualified electrician so this job is quite within my capabilities.

I am fitting a new radiator to my system and I will be teeing off the existing 22mm pipework just to feed one new radiator. Now I see the advantage if supplying 2 radiators, with keeping to 22mm as long as possible in the run and teeing off in 15mm, ie the 22mm will be better at supplying enough water to supply two rads when they tee off in 15mm pipe. But if I am coming from 22mm pipe is there any benefit staying with 22mm as long as possible in the run if I am supplying only 1 rad (a big one), or might I just as well drop straight to 15mm pipe straight away for ease of work?

I know the smaller pipe is cheaper but I have enough of both already to do it either way.

I know there is this thing where they compare water flow to electrical current or something but it always looses me.

I would guess it would be better to drop to 15mm straight away, instead of staying at 22mm for a while as it would get restricted down anyway where ever I change to 15mm so there would be no benefit staying with 22mm. Can anyone clarify?

I am sure there is a clever answer to this but I will need some guidance please, and maybe some reasons why to do it one way or the other if possible?

 

[chrishutt]

15mm tube is adequate to supply several radiators, up to a total load of about 6 kW. You could use 10mm or even 8mm tube for your single rad. It's analogous to current flowing in cables against resistance. If you oversize the pipes to the radiator you will need to close down the rad lock-shield valve to balance it's resistance with other circuits.

 

[happyhero]

Sorry forgot to mention I will be fitting a Drayton thermostatic valve to this radiator as well.

chrishutt thanks for your reply, I am interested in what you said about closing down the rad lock shield valve which I understand as the valve that is not my thermostatic valve. Am I right?

I have heard of people balancing their system but I have not done this. I have a thermostatic valve on all my radiators except my bathroom one which I understand is the right way to do it, ie leave one radiator unchecked by a thermostatic valve to allow a flow if they all shut down.

I also have all my valves on the other side of the rads fully open. What would be the difference if I started playing with turning them down? At the moment they all get hot but I wouldn't mind more heat in a couple if it were possible. I assume I would be getting involved in balancing the system if I did do this?

Can you enlighten me a little please?

 

[chrishutt]

Can you enlighten me a little please?

Balancing is quite a complicated process which has been covered several times before, and which is probably dealt with in the FAQ topic and maybe the Wiki.

With TRVs on all the rads a system will tend to be self-balancing, once it's all up to temperature. However if you've one or two rads where the return temperature is much lower than on the others (with TRV fully open) you could try closing down all the other lock shield valves, especially any where the rad return temperature is particularly high. You are aiming for an equal temp. drop across all rads (typically 11°C or 20°C depending on system design).