The subject of the invention is a boiler having two outlets of heat-transfer fluids at different temperatures. It is constituted by the combination, on the one hand, of a heat generator with a burner 1, a combustion chamber 2 and very high-temperature water spaces 2' connected to the distribution and return pipes 14, 15 and then by a peripheral regenerator 5, 5' connected to a low-temperature heat-producing and -distributing chamber connected to an underground root-heating system 8 with recycling of the heat-transfer fluid with a counter-flow 7, 9 by vaporisation and rings forming baffles. It is intended more particularly in agricultural applications to produce two heat-transfer heating fluid loops, one at very high temperature and the other at low temperature, having outlets which are either alternate or are simultaneous. <IMAGE>
