12-radiator system, new-build extension

A two-storey rear extension on a 1960s detached house in Belper, and the existing heating system suddenly had to do double the work. The homeowners had specced 12 radiators across both floors, two heating zones, and underfloor in the new kitchen-diner. Add to that a desire for a proper smart thermostat with per-room control.

Before we started, I sat down and ran the heat-loss calculations for the extended footprint. The existing 22mm flow couldn't carry the additional load — the boiler was big enough, but the pipework would have been a bottleneck.

Day one and two: re-piped the primary run in 28mm copper from boiler to the airing cupboard, and added a low-loss header so the old and new sides of the house each run their own loop without competing. The header is the difference between a heating system that works and one that just about works.

Days three through five: rads in, underfloor laid and pressure tested, smart thermostat wired through, system filled and balanced. TRVs on every radiator, two-port valves on the zone splits, full commissioning report left with the customer. The customer wrote in afterwards: "Five radiators, underfloor in the kitchen, smart thermostat. Done in three days, tested, and working perfectly."