Telford Direct Combination Cylinders When the only energy source available is electricity, a direct pattern cylinder is the ideal product. The domestic water is "directly" heated by the immersion heaters which sit inside the 2"1/4 boss within the cylinder. However, the heat-up and recovery times take longer than an indirect cylinder. Extra immersions are available on request.telford Please note - Vented Cylinders are not supplied with an immersion. Deciding on the right sort of Cylinder is an important decision. After you decide that Direct Combination Cylinders are the right solution then the Telford Direct 144L Combination Cylinder - BCD10545VF is no doubt worth a serious look.