CENTRAL HEATING PIPE RUNS

You can just carry on from the hall in 15 mm to the front room.there's more than enough heat capacity in 15mm pipe to work multiple rads.

My first house was run in 22mm up the middle (centre) of the house from back boiler then a 15mm f+R came off to do the front rads (4 off) and another 15mm F+R went the otehr way to do the back of the house (6 rads) Worked brilliantly.

It's ok as long as the total heat output of the radiators on your 15mm drop doesn't exceed about 6kW. The radiators need to be connected in parallel - not in series - of course.

Dont want to appear thick but "The radiators need to be connected in parallel - not in series - of course." What does that mean?.

Thanks Set Square and also GymRatz for the reply.

In a conventional modern two pipe system, you have a 'flow' (from the boiler) and a 'return' (back to the boiler) pipe and all your radiators connect from one to the other and thus are in parallel.

Years ago it was not uncommomon to have a 'one pipe' system, where a single pipe ran arround the area to be heated from the output to the input of the boiler, and each radiator was in parallel with a short section of this pipe (usually the length of the radiator) - this is the system often found in schools and municiple buildings - the pipe often being 2" black iron. Here effectively the radiators are in series with each other.

AWEM

My mother-in-law has a really odd system that seems to have been originally a DIY install, probably 30 or 40 years ago. Some aspects are rather good - curved radiators in the bay windows for example - but others are decidedly silly; there is no room thermostat and she regulates the house temperature by adjusting the boiler thermostat.

The layout of the pipework is rather complicated too and appears to be a mixture of three different systems thus:

Series would be if the feed pipe went to one rad and the output from that rad fed the other one - so that the *same* water flows first through one then through the other. Parallel is where the feed pipe splits and goes to one side of each rad, and similarly with the return pipe - so there is an independant path through each rad - so that you can turn one off wthout affecting the other.

Same as the electrical analogy of wiring resistors in series or parallel, really.