Electric systems have to meet minimum energy performance standards regarding the tank’s heat loss. Today we strongly recommend checking with your energy provider about off peak rates and tariffs that may apply to hot water units.
Today’s continuous electric hot water units rarely run out of hot water – at least not for a very long time. A four person household may require a hot water system between 125-160 litres. Running your hot water like this can be the most expensive. Continuous hot water basically means you have hot water on demand when you need it.
Off-peak or night-rate systems only receive power for a period during the night. Tank heat losses and hot water that’s used is not replaced until the following night. So you need a large tank that can cope with your day’s demand, otherwise you may end up without hot water (about 250–315L for a four-person household). Twin-element tanks can be a good option. The bottom element is connected to off-peak supply and does most of the heating. If you run low on hot water, a second element connected to continuous supply kicks in to heat a small portion of water at the top of the tank.