  In this article, we present a cost-effective approach to the precision
measurement of heat flux using commercial thermoelectric modules (TEMs). Two
different methods of measuring heat flux with TEMs are investigated, namely
passive mode based on the Seebeck effect and active mode based on the Peltier
effect. For both modes, a TEM as a heat fluxmeter is calibrated to show a
linear relation between the voltage across the TEM and the heat flow rate from
0 to 100 mW. While both modes exhibit sufficiently high sensitivities suitable
for low heat flow measurement, active mode is shown to be $\sim$7 times more
sensitive than passive mode. From the speculation on the origin of the
measurement uncertainty, we propose a dual TEM scheme by operating the top TEM
in passive mode while its bottom temperature maintains constant by the
feedback-controlled bottom TEM. The dual-TEM scheme can suppress the
sensitivity uncertainty by up to 4 times when compared to the single-TEM
passive mode by stabilizing the bottom temperature. The response time of a 1.5
cm $\times$ 1.5 cm TEM is measured to be 8.90 $\pm$ 0.97 seconds for heating
and 10.83 $\pm$ 0.65 seconds for cooling, which is slower than commercial heat
fluxmeters but still fast enough to measure heat flux with a time resolution on
the order of 10 seconds. We believe that the obtained results can facilitate
the use of a commercial TEM for heat flux measurement in various thermal
experiments
