Electric immersion heaters are a popular choice where a gas
supply is not present. Gas water heating usually has lower run
cost. How they Work - There is a jacketed heating element in the
water cylinder. - Usually the element has a built in adjustable
thermostat, but there are also some with no stat built in, and a
separate external stat attached to the tank, usually at about
1/3 the way up the tank. - There is an on/off switch (or
occasionally a timer) on the supply to the heater. - Newer
elements also have a secondary thermal cutout built in 2 Element
Systems Economy 7 Systems Dual tariff systems typically heat the
lower element at night, and use the smaller top element for top-
up heat in the day. 27" elements heat the whole cylinder. This
is the most common size. 11" elements are used for top heat
only, and for whole cylinder heating with Fortic cylinders. 14",
18" 30" and 36" elements are also available, but are less common
than 11" & 27". The element should generally be 3" - 6" shorter
than the max lengt