Pan-type apparatus to fry or boil food products in a suitable liquid, comprising: - a pan to contain the liquid; - a first internal casing which delimits inside itself a closed housing chamber which houses at least part of the pan; - burner means disposed in the housing chamber and suitable to generate a flame which, directly or indirectly, heats the pan; - flue means to extract the combustion fumes from the housing chamber; - separation means disposed in the housing chamber and suitable to define at least a first chamber adjacent to the pan, which houses said burner means, and a second chamber, between the first chamber and the walls of the first internal casing, which communicates on one side with the first chamber and is connected on the other side to said flue means, characterized in that the separation means are disposed on one side and on the other with respect to the pan and comprise at least two pairs of separation walls (25, 27), each pair of separation walls comprising a first internal wall facing toward the pan, and a second external wall facing toward the peripheral walls of the first internal casing, disposed between said pan and the first wall, each pair of separation walls (25, 27) being disposed on one side and the other with respect to the pan so as to define, for each side with respect to the pan, a pair of chambers (26, 28), formed by a corresponding first chamber and a corresponding second chamber, a conveying path being defined for the fumes between the first chamber and the second chamber of each pair of chambers (26, 28), and from the second chamber toward said flue means, so as to determine a forced transit of the fumes for a determinate transit time, both to lap the pan in contact along said first chamber, and also laterally to the pan at least along the second chamber. - a pan to contain the liquid; - a first internal casing which delimits inside itself a closed housing chamber which houses at least part of the pan; - burner means disposed in the housing chamber and suitable to generate a flame which, directly or indirectly, heats the pan; - flue means to extract the combustion fumes from the housing chamber; - separation means disposed in the housing chamber and suitable to define at least a first chamber adjacent to the pan, which houses said burner means, and a second chamber, between the first chamber and the walls of the first internal casing, which communicates on one side with the first chamber and is connected on the other side to said flue means, characterized in that the separation means are disposed on one side and on the other with respect to the pan and comprise at least two pairs of separation walls (25, 27), each pair of separation walls comprising a first internal wall facing toward the pan, and a second external wall facing toward the peripheral walls of the first internal casing, disposed between said pan and the first wall, each pair of separation walls (25, 27) being disposed on one side and the other with respect to the pan so as to define, for each side with respect to the pan, a pair of chambers (26, 28), formed by a corresponding first chamber and a corresponding second chamber, a conveying path being defined for the fumes between the first chamber and the second chamber of each pair of chambers (26, 28), and from the second chamber toward said flue means, so as to determine a forced transit of the fumes for a determinate transit time, both to lap the pan in contact along said first chamber, and also laterally to the pan at least along the second chamber.