Water heating element – arc, 2.5 kW

The working length is the first thing to check on this arc: 37.5 cm, give or take 5%. The tube must sit fully under water and still clear the far wall of the tank.

Then the fittings: 14 and 16 mm, spaced 60 mm centre to centre, the same as every arc in the row. Terminal studs are threaded M3.

Two and a half kilowatts is a sensible middle for a mid-sized tank — noticeably brisker than the smallest sizes, yet it does not need its own circuit the way five kilowatts does. The tube is stainless steel, 10 mm in diameter. Hard water leaves scale on any heater, so pull it out and look it over once a season.

• Power — 2.5 kW
• Working length — 37.5 cm
• Fitting diameter — 14 mm, 16 mm
• Tube diameter — 10 mm
• Material — stainless steel
• Terminal thread — M3
• Centre distance — 60 mm