While internal insulation of hot water cylinders is improving, significant heat loss still occurs with all storage cylinders, including solar boosted cylinders, regardless of age. See this article for summary of typical energy loss of hot water cylinders.
Unless your water heater's storage tank already has a high R-value of
insulation (R>4.0), adding insulation to it can reduce standby
heat losses by 25%–45%. This will save you around 4%–9% in water heating
Hot water cylinders do not generally advertise their R value rating in Australia. If you don't know your water heater tank's R-value, touch it. A tank that's warm to the touch needs additional insulation.
A cheaper alternative is to buy a roll of foil backed insulation (Bradford Anticon). The rolls are 15 m long, enough to do at least three large cylinders. Share a roll with family!
CLICK HERE for instructions on installing additional insulation to electric storage hot and solar hot water systems from US Department of Energy.
Alternatively, a shelter or cover can be built around the cylinder if it is exposed to the outside elements, sheltering it from the weather. This can be further improved by lining the walls with a reflective material such as sisalation to reflect radiant heat emitted from the tank, reducing the heat loss. Otherwise the shelter can be packed with spare insulation batts.
When wrapping a cylinder remember to keep the thermostat panel at the bottom of the tank and presssure relief valve accessible for maintenance.
Bradford Anticon can be bought from
Cowleys Interior Supplies Pty Ltd
Becks Hardware (Span Truss Systems)