The Super Coil unvented cylinders have a unique, integrated expansion solution factory fitted. All pipes & connections are also hidden under an insulated top lid. Factory fitted components drastically reduces fitting time, making the Super Series virtually a pre-plumbed unit. Duplex Stainless Steel makes the Super Series extremely lightweight & space efficient for easy handling & installation. Low heat loss, dedicated secondary return, impressive heat up & recovery times and a 25 year guarantee.