For a given mass flow rate of air, induced-draft operation in principle entails greater power
consumption than forced-draft operation due to the higher volumetric flow rate of the
heated air that is handled by the induced-draft fan. In practice, however, this potential
disadvantage tends to be offset by the more uniform flow distribution and lower potential
for hot gas recirculation obtained with induced-draft operation. As a result, induced-draft
units typically do not require significantly more power than forced-draft units and in some
cases may actually require less power. If the difference between fluid outlet temperature (required) and ambient air temperature is less than 300C, induced draft unit is preferred because of the less percentage recirculation of hot exhaust air. But if the same is more than 300C, forced draft unit is preferred as it consumes less power