Domestic immersion heaters and replacement immersion heater elements are sized by their BSP (British Standard Pipe) thread, which screws into the boss on your hot water cylinder. The most common UK sizes are 1¾" BSP, found on most modern direct cylinders; 2" BSP on older or larger tanks; and 2¼" BSP on some traditional indirect cylinders. If you're replacing an existing immersion heater element, match the thread on the unit you're removing. If fitting to a new cylinder, the boss size will be in the manufacturer's specification.

Standard Incoloy immersion heater elements are the right choice for most domestic installations: reliable, cost-effective, and well suited to normal mains-pressure systems. In hard water areas, limescale accumulates on the element surface and shortens its working life considerably. Titanium domestic immersion heaters and elements resist this significantly better; they cost more upfront but typically outlast Incoloy in hard water conditions by a meaningful margin. If you're replacing immersion heater elements more than once every few years, the switch to titanium is worth the investment.

Standard 3kW immersion heater elements draw more power than most solar thermal or heat pump systems can consistently deliver. The eCo Heat range of domestic immersion heaters runs at lower wattage to match the output profile of these systems, reducing reliance on a boost element and improving overall efficiency. If your hot water cylinder sits within a solar or heat pump setup, eCo Heat immersion heater elements are the straightforward, purpose-built choice.