Abstract: A method for producing a channel arrangement, a channel arrangement, a metal profile and use of a channel arrangement. The method includes arranging a first metal profile towards a second metal profile. The first profile includes elongated trench-like portions mutually separated by flat portions. The first profile is joined to the second profile so that channels between the first profile and the second profile are defined. The channels are separated by flat regions. In the arranging, at least one of the profiles is a profile including an incipient cut to be located in at least one of the flat regions. Material is removed from the at least one flat region so that the thickness of a part of the at least one flat region becomes less than the sum of the thicknesses of the profiles.

Abstract: The invention relates to a heat exchanger unit to be used in a gas-fired water heater in which heater a heat exchanger unit contains tubes with fins. According to the invention the heat exchanger unit contains flat oval tubes (1,21,31) having a fin (3,22,32) at least on one flat part (4,24,33). The flat oval tubes (1,21,31) as well as the fins (3,22,32) are made of copper, copper-based alloy, aluminium or aluminium-based alloy.