For high hot water demand situations where an instant and continuous supply of hot water is required or for occasional high usage situations a plate hot water system offers a highly efficient and practical space saving solution with a system that occupies a fraction of the space used by traditional calorifiers and that removes the requirement to inefficiently store large volumes of water in readiness for possible demand that may never come. Traditional calorifiers are an inefficient waste of energy that can also increase Legionella risk.