The bypass factor (B. P. F.) in case of sensible heating of air is (Where td₁ = Dry bulb temperature of air entering the heating coil, td₂ = Dry bulb temperature of air leaving the heating coil, and td₃ = Dry bulb temperature of heating coil)
(td₃ - td₂)/(td₃ - td₁)
Nusselt number (NN) is given by
In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)