My existing (old) CH system uses a single pipework loop downstairs and a single pipework loop upstairs - ie the radiators are in series with the pipework rather than in parallel as modern systems. I am told that you cannot use this arrangement with the new high efficiency condensing boilers and that the pipework must be changed to a 2 pipework system (separate flow and return). I realise a 2 pipework system is more efficient, the radiators heat up more quickly and the system can be properly balanced. But do I have to change ... is this correct ... and if so, why ?
Single pipework systems can be still be retained with some modern condensing boilers (always best to check with boiler manaufacturer), but to ensure boilers condense efficiently, the flow and return differential temperature must be 20 degrees (i.e 70 degrees flow 50 degrees return).
Should a single pipe system be used, this return differential cannot be guaranteed and the efficiency of the boiler could be adversely effected.
Best practice and boiler interlock under part L Building regs require a Programmer/Room stat and thermostatic radiator valves to be fitted for control of the boiler/reduced emissions.
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