Insulating hot water tanks
Although you could in theory lag your hot water tank by adapting any of the methods that are used for cold water tanks, in practice you will nearly always find that you have no choice but to use a proprietary jacket. The fact that most hot water tanks are situated in airing cupboards means that blanket insulation is out of the question, and unless your tank is a rectangular one (which these days are very rare) you won’t be able to use polystyrene.
Proprietary jackets for hot water tanks are made of the same materials as those used on cold water tanks and are just as easy to fit. The system used to fasten the jacket to the tank varies, but basically at the top you secure the ‘envelopes’ round the hot water supply pipe with a loop of cord, while further down you hold them in place with straps. The base of the tank is left uninsulated, as is the capping and wiring of any immersion heater.