Direct Cylinder – Heated by an electric immersion heater only. Not suitable for connection to a Boiler. Unvented Cylinder – Pressurised unit, fed directly from mains water. No header tank required. The Neptune Cylinder is an unvented hot water storage system which is an ideal compliment to the Fusion & SlimJim Electric Boiler range. Like all our products, the Neptune Range is manufactured to the highest standard and offers a high performance to suit your needs. The Neptune range provides fast flow rates, energy efficient insulation, quick recovery coils, and the use of an external expansion vessel to reduce maintenance. Additionally the 3 bar operation of the unit meets all modern criteria for fast flow applications. The Neptune Indirect cylinder is suitable for providing hot water with all types of boilers: gas, electric, oil, solid fuel and LPG, complete with two 3kW immersion heaters.