The water heater has an upright water tank, an exhaust flue extending through the water tank, a combustion chamber arranged under the water tank, an atmospheric gas burner in the combustion chamber and a complete pre-mixing gasair supply system with outside gas and air intakes. Such transducers are detachably mountable on an envelope of the flow path. A plurality of insights can be extracted from the obtained data, resulting in extracted insights. The modulation control means produce a number of macropixels from at least two adjacent pixels, to which a selected modulation characteristic is assigned.