# Heat Flow Rate

Heat flow rate, abbreviated as \(Q_f\), is the rate at which heat moves from an area of higher temperature to an area of lower temperature. Btu/hr (W/hr). Heat flow is generally used to quantify the rate of total heat gain or heat loss of a system.

### Heat Flow Rate FORMULA

\(\large{ Q_f = -k \left( \frac {A} {l} \right) \Delta T }\)

Where:

\(\large{ Q_f }\) = heat flow rate

\(\large{ A }\) = area of the emitting body

\(\large{ l }\) = length of the material

\(\large{ \Delta T }\) = temperature differential

\(\large{ k }\) or \(\large{ \lambda }\) (Greek symbol lambda) = thermal conductivity