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The unvented system operates purely from mains water. The principles of heating are the same, but because everything is under the pressure of the mains water, flow rates are much better...Many safety devices are built into this system to accommodate for the greater pressure and expansion of the water. Although a small tank may be found in the loft for venting and feeding your central heating, No cold water storage tank is necessary.
Hot water cylinder capacity varies between 25 gallons to 50 gallons for normal domestic supply, with the larger being enough to supply an average family for a day. Most cylinders are made from thin copper and you should make sure your cylinder is well lagged to prevent heat loss. Pre-lagged cylinders are available, which are coated with foamed polyurethane.
Shower coils can be fitted to all styles of cylinder and combination tanks, connected directly to the mains and gaining heat quickly from the store of hot water in the cylinder they provide effective and efficient power showering. Particular efficiency is achieved if finned tube is used in the manufacture of the shower coil.