Abstract: A method for exchanging heat between a primary fluid (W) and a secondary fluid (X) and a heat exchanger for heat exchange as well as an arrangement and a kit comprising a heat exchanger. The heat exchanger comprises a first and a second fluid circuit extending through the heat exchanger. The heat exchanger further comprises a stack of fluid plates and a membrane arranged between each of the fluid plates where one interspace is formed between each fluid plate and membrane. The first and the second fluid circuit are each constituted by a passage extending through the fluid plates and membranes and along the fluid plates and membranes in at least two interspaces. A primary fluid (W) is passed through the first fluid circuit and a secondary fluid (X) is passed through the second fluid circuit such that the primary fluid (W) is passed along one side of a membrane and simultaneously the secondary fluid (X) is passed along the other side of the membrane.