Hi everyone. I am currently carrying out an experiment whereby I have a closed tank of water submerged in a larger tank. The water in the smaller box is heated and I am interested in the heat loss from the tank. I have done a rough theoretical calculation based on U values, where by I obtain: Q (heat loss) = A*U*DeltaT and end up with a value of 10W. I have calculated the Wattage of the heat source I am supplying to the box as 1KW so in theory this should mean the heat loss will be negligible, correct? Obviously this heat loss calculation is only rough, I had to calculate U values from calculated resistance values of the materials (as the walls of the tank are of composite construction) by the relation R=d/k where d is the thickness of the material and k is the thermal conductivity of the material. Then calculated the U value as U=1/(R1+R2+R3). Providing this is even correct the calculation will still be rough as I am not taking into account any thermal bridging effects of the joins in the tank etc. I want to check this calculation experimentally, to do this I will fill the tank with heated water, seal it and then submerge it in the larger tank of cooler water and monitor the temperature drop within the small tank. I am then just a little puzzled as to how to relate this to my theoretical calculation and obtain Q (the heat loss) from the experimental data. Will I just use Newton's law of cooling and the relation: T=(Tint - Toutside)*exp(-A*t/m*C*R) + Tout to calculate R from the experimental data and then plug this back in, in the form U=1/R to my initial calculation for Q above and compare? Any help/advice would be much appreciated.