Abstract: A test apparatus is provided for testing the heat transfer resistance of a tube, such as a tube of a heat exchanger, the apparatus including a heating means, such as a block of metal surrounding and engaging a part of the tube, with an electric heater for heating the block, the block including at least two termistors at different distances from the tube to measure heat flux. A pump causes water to flow through the tube, and a thermistor measures the water temperature. A flow meter and a pressure drop sensor for sensing the drop in pressure across the block are also provided. The measuring devices other than the flow meter provide, preferrably, analog output signals, which are converted and supplied to a computer for computation of total heat transfer resistance, convective heat transfer resistance, conductive heat transfer resistance of the tube and friction factor.