Central heating extension

20 Jul 2005
Reaction score
United Kingdom
I will soon be extending my house to increase the size of the kitchen and add a new utility room and cloakroom. I will need to extend my central heating to cover these areas.

The present system is the old fashioned “one pipe” system where all 7 existing radiators sit atop a single circulating loop staring in 22mm as it leaves the boiler and then reducing to 15mm at the first upstairs radiator. The 15mm pipe then runs along the first floor bathroom and bedrooms before desending downstairs and repeating the process on the ground floor. At the last radiator, the pipework returns to 22mm for the final 5 metre run back to the boiler.

About 7 years ago I started to upgrade the system, by removing the old primatic cylinder and converting it to a fully pumped “S” plan. As winter was starting I left it at that, intending to upgrade it to a 2 pipe system the following summer. However, the system worked so well that, I have never upgraded it and have since added new wooden floors and fitted bedroom furniture above the pipe which I do not want to disturb.

What would be the best way to extend the system to feed 3 new radiators and a towel rail in the extension? Should I extend the end of loop (4 new bends & 20 metres) to cover the new extension and bury it in the new concrete floor, (it can’t be at skirting level and boxed in because of several doorways) or can I tap into the loop upstairs before the first radiator, feed the new radiators and then take their returns back to the boiler as a two pipe arrangement, or will this disturb the balance of the existing system. Any other suggestions welcome except rip out the old one pipe system and replace it.
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