NOTE: Due to the relatively complex nature of heat transfer, results gained from application of these formulae, while useful, must be treated as approximations only. Design safety margins should be considered before final selection of any device.

1) Heat gained or lost through the walls of an insulated container:

Where:

Q = Heat (Watts)
A = External surface area of container (m²)
DT = Temp. difference (inside vs. outside of container) (Kelvin)
K = Thermal conductivity of insulation (Watt / meter Kelvin)
DX = Insulation thickness (m)

2) Time required to change the temperature of an object:

Where:

t = Time interval (seconds)
m = Weight of the object (kg)
C_p= Specific heat of material (J / (kg K))
DT = Temperature change of object (Kelvin)
Q = Heat added or removed (Watts)

NOTE: It should be remembered that thermoelectric devices do not add or remove heat at a constant rate when DT is changing. An approximation for average Q is:

3) Heat transferred to or from a surface by convection:

Where:

Q = Heat (Watts)
h = Heat transfer coefficient (W / (m² K))

(1 to 30 = "Free" convection - gases, 10 to 100 = "Forced" convection - gases)

A = Exposed surface area (m²)
DT = Surface Temperature - Ambient (Kelvin)

Conversions: