A plasma channel (filament) formed in the electromagnetic field of microwave (MW) radiation shows promise for its application for off-body non-electrode modification of a gas flow (plasma aerodynamics) and in the plasma assisted combustion process. In these problems, the channel is considered as an object that converts the energy of electromagnetic radiation into gas heating. To estimate the total power absorbed in the plasma from above, simple formula is obtained. Numerical calculations in air in the pressure range P = 20-100 Torr based on a simplified 2D model using a fairly complete system of plasma-chemical reactions have shown that the total absorbed power is close to its estimate from above when the plasma channel develops.