Abstract A novel multi-fluid heat exchanger deployed for simultaneous heating of water and space is experimentally investigated to predict its thermo-hydraulic, exergetic, and sustainability performance for distinct Al2O3, TiO2, and CuO nanofluid (NF) flow of 50 ppm concentration of each through the inserted brazed helix tube (BHT). The input parameters such as flowrates, helix tube diameters, and nanofluid types are varied throughout the experiments to evaluate their effect on output performance parameters i.e., Nusselt number (Nu), friction factor ( f), entropy generation number (Ns), JF factor (JF), exergy efficiency (ƐE), and sustainability index (SI). The NF flowing through the BHT is the heating fluid that simultaneously heated the cold water, and cold air flowing through the outer shell and inner conduit of the BHT respectively. A distinct Nusselt number correlation for turbulent nanofluid flow inside BHT was developed, compared, and validated reasonably with the current result. For Al2O3 NF at a Reynolds number of 5698 with a 1/2-in. diameter helix tube, the best results for JF, ƐE, and SI are found to be 0.009, 0.72, and 3.53, respectively. Furthermore, for Al2O3 and TiO2 NF at a Reynolds number of 14,250 and a helix tube diameter of 3/8 in. and 1/2 in., f, and Ns are found to be 0.0047 and 0.043, respectively are minimum. It is observed that the use of Al2O3 NF, higher helix tube diameters, and lower flowrates all make the proposed heating application more sustainable.