The ratio of the Joule heating and conduction cooling terms in the macrosco
pic energy equation of electrons in an ionized gas is examined under condit
ions which may include saturation of the heat flux. The saturation flux may
be represented in quantity alpha nkT(kT / m)(0.5), where n, T, and m are,
respectively, the electron density, temperature, and mass, and alpha may be
of the order of 0.1. Consequences of this assumption are developed for app
lication to the question of Joule heating of electrons by 100 Hz electric f
ields in the Venus ionosphere. When saturation exists, there can be large o
verestimates of the conduction cooling, and corresponding underestimates of
the temperature, if the classical Spitzer-Harm formula is employed. A mini
mal reduction factor to apply to this cooling rate is presented. Taking int
o account both the existence of saturation and the burst nature of the 100
Hz fields, it is shown that Joule heating by observed fields may balance co
nduction cooling in parts of the Venus ionosphere. In particular, this occu
rs at, and somewhat below, high Venus ionopauses. It is suggested that more
research on these regions may add to our knowledge of saturation.