Excess heat from a source such as a fireplace is absorbed into a liquid medium and transferred to storage for later use or to a distribution network for radiation at remote locations. The fireplace can be formed by heat conducting walls of a multi-chambered enclosure having an air guiding path for heating the air along with a liquid medium passing through the enclosure in a heat exchanger arrangement. The heated liquid medium can be stored and, when there is no combustion in the fireplace, returned to the fireplace enclosure for supplementary air heating. The liquid medium storage can include a tank having a pair of baffle plates in generally horizontal but diverging relation for producing heat layer stratification and separation of the liquid medium. Both cool and warm liquid medium are delivered between the baffle plates in proximity to the end of minimum vertical separation.