Method and apparatus for heat recovery

Apparatus for recovering heat in water and waste pipe systems, comprising a main supply pipe for cold water, a water heater supplied with water from said supply pipe, a waste pipe which is supplied with waste water from different consumption points and a heat exchanger which is connected with the waste water pipe and is connected between said supply pipe for cold water and the water heater for providing a preheating of the cold water by means of the waste water before the cold water is supplied to the water heater, wherein the apparatus is provided with a branching point before the heat exchanger, from which a first pipe extends to the heat exchanger and a second pipe extends past the heat exchanger and the apparatus comprises a detector and control device for determining the relationship between the temperature of the waste water escaping from said consumption points upstream from the branching point and the temperature of the waste water in the heat exchanger and for directing the escaping waste water to the heat exchanger if the temperature of the waste water therein is lower than the temperature of the escaping waste water and in the opposite case directing the escaping waste water past the heat exchanger.