We investigated the magnetic and heating properties of ferrofluids made of magnetic nanoparticles having a nanoflower structure dispersed in water or polyethylene glycol. In both cases, the magnetic behavior of the fluids is ruled by the effect of magnetic interactions, and these show a higher intensity when the dispersing medium is water with respect to the polyethylene glycol case. Also the ferrofluids heating power is different, as the one made of water turns out to be more effective for what concerns the temperature increase. Both result are in favor of a modification of the nanoflower structure induced by the carrier fluid.