# Overall Heat Transfer Coefficient

Overall heat transfer coefficient, abbreviated as U, is the heat transfer between items like walls in buildings or across heat exchangers for the conduction within materials.

### Overall Heat Transfer Coefficient Formula

\(\large{ \frac{ 1 } { U \; A } = \frac{ 1 } { h_1 \; A_1 } + \frac{ dx } { k \; A } + \frac{ 1 } { h_2 \; A_2 } }\)

Where:

\(\large{ U }\) = overall heat transfer coefficient

\(\large{ A }\) = contact area for each fluid side

\(\large{ A_1 }\) = contact area for one of the fluids

\(\large{ A_2 }\) = contact area for the other fluid

\(\large{ dx }\) = wall thickness

\(\large{ h_1 }\) = individual heat transfer convection coefficient for one of the fluids

\(\large{ h_2 }\) = individual heat transfer convection coefficient for the other fluid

\(\large{ k }\) = thermal conductivity of the material