Existing Flat plate solar thermal collectors suffers from comparatively low efficiency. This clearly indicates that further research is still needed in the area to improve efficiency of those types of collectors by employing different techniques. Therefore this study aims to evaluate how different parameters like spiral tube arrangement, working fluid flow rate and thermal characteristics affect the thermal efficiency of a flat plate solar collector. An experimental test is conducted for five different fluid flow rates. In order to investigate the effect of the fluid thermal characteristics on the efficiency of the collector water, Cuo and nanofluids with two different nanoparticle volume concentrations are used. The numerical simulation of the collector has been performed by means of the Finite Volume Method (FVM) using commercial ANSYS Fluent 19.2 software. Both the numerical and experimental results showed that the spiral type flat plate collector shows a greater efficiency than the conventional type of collector. The collector efficiency was maximum for all the fluid types when the fluid flow rate is fixed at 2L/m. and generally the efficiency obtained for all the working fluids during the experimental test at the optimum 2L/m fluid flow rate was 60.3 for water, 66.5 for Cuo nanofluids and the maximum efficiency belongs for Nano fluid which is 68% at 0.4% nanoparticle volume concentration. The results obtained from the experimental test as well as the numerical results are fairly in good agreement with only a maximum of 2.85% deviation that shows the simulations were quite satisfactory. Key words: flat plate collector, collector efficiency: spiral tube: nanofluids: finite volume method.