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An overall heat transfer coefficient h<sub>overall</sub> can be calculated for a given system, given its heat transfer behavior, so that it can be described by Newton’s Law of Cooling:

<math>q = h_{overall} \cdot A \cdot \Delta T</math>

where q is the heat transfer rate, h is the heat transfer coefficient for the system, A is the area of heat transfer, and delta-T is the temperature difference between the zones of heat transfer.  This description of heat transfer can be applied to the combined effects of conduction, cooling, and radiation.

Generally, for a body at some temperature T<sub>body</sub> in a reservoir of fluid T<sub>fluid</sub>:

<math> \Delta T = T_{body} - T_{fluid} </math>

==Deriving the Overall Heat Transfer Coefficient==

If the heat transfer rate is known, then h<sub>overall</sub> can be derived directly from Newton’s Law of Cooling.  However, if the other thermal characteristics of the system are known ([[heat transfer coefficient|heat transfer coefficients]], [[thermal conductivity|thermal conductivities]], and [[emissivity]]), the overall heat transfer coefficient can be calculated from the thermal resistance for simple systems.

<math>h_{overall} = \frac{{1}}{{R_{total}}} </math>

where A is the area of the heat transfer surface and R<sub>total</sub> is the total thermal resistance of the transfer surface.

Thermal resistances in series, like electrical resistances in series, are additive.  So, for heat passing into a wall by convection, through the wall by conduction, then out by a combination of convection and radiation, the total resistance is equal to the sum of the resistances at each step.  

<math>R_{total} = R_{in} + R_{through} + R_{out} </math>

h is analogous to thermal conductivity, and R can be defined relative to thermal conductivity just like it can relative to h.  So,

<math>R_{total} = A \cdot ( \frac{{1}}{{A_{in} \cdot h_{in}}} + \frac{{t}}{{A_{mean} \cdot k}} + \frac{{1}}{{A_{out} \cdot h_{out}}} )</math>

which can be inverted to obtain the overall heat transfer coefficient.

*see also: [[Thermodynamics of the greenhouse]]

{{MainArticle|[[Heat transfer|Heat Transfer]]}}