Basics and Some Theory of AnTherm
Calculation Model
Using the concept of a conductance, L_{ij} (between the spaces
i and j), the heat which flows out of space i is a sum
depending on the temperatures of space i and of all other spaces, j:
Since L_{ij} can be proven to be symmetrical (= L_{ji}),
this equation corresponds formally to Kirchhoff's law of electrical networks.
The analogy that this allows is quite significant: the spaces of a building
construction (model) can be thought of as nodes in a heat conducting network.
equation model 
Thus the heat conduction model, otherwise only describable
with partial differential equations, can be mathematically defined as a
relatively simple, linear system of equations with a given conductance
matrix. Furthermore, only the thermal coupling between spaces which
interchange heat directly through the building component ("neighbouring
spaces") is of practical effect; coupling between indirectly connected
spaces is generally negligible.

boundary conditions 
As the equation above shows, in addition to the appropriate
value in the conductance matrix, either air temperature or heating load must
be defined for each space of the model (evaluation boundary conditions) in order to
attain a complete description of a particular heat flow situation. 
