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If you have a hot water cylinder (and nine million UK homes do) how long will it last before you need to heat the water again? If you don’t know, it will only take a day or so to work it out; you might find that you can start saving money by not heating the water as often. You could also be losing heat from the cylinder itself: modern cylinders should lose no more than 2kWh a day and some lose as little as 1kWh; copper cylinders with loose red jackets can lose up to 4kWh, although the loss will depend on insulation thickness and size of the cylinder – the bigger the cylinder the more it will lose – but it can soon add up to over 1,000kWh a year. For practical advice on protecting your cylinder from heat loss, visit