Thermal mass flowmeters are based on the relationship between convection heat transfer and mass flow. There are two types of thermal mass flowmeters: Rate of Heat Loss Flowmeter and Temperature Rise Flowmeter.

Governing equation:

In this equation, , V_avg, qt, and T are the unknowns, because they change with time while the other variables are known. However, qt and T can be obtained through measuring devices, leaving in the product of and V_avg and cross section area of the pipe.

Temperature Rise Flowmeters measure the temperature of the flow changes as it passes through a heat source.

Governing equation:

W and T are unknowns in this equation. T can be measured. W can therefore be calculated.

Note that thermal mass flowmeters are used for gas measurements only.