Temperature and heat
An house is a closed volume where agreable temperature is wanted, mainly in winter, so that coats, gloves and fur boots are not needed, when outdoor temperature is very low. The heat contained in an object placed in a colder environment flees in it in the same way as the water in a mountain lake flees toward the sea.
The gap of altitude of the water is the gap of temperature for the objects regarding the environment. The water flow is like the amount of heat that the objects loses into the colder environment, which is the thermal energy flow. The lake empties, the object cools. The thermal energy flow that goes from the warm object into the colder environment depends on the gap of temperature, and of the ease with which the energy can travel from the object to the environment.
It can be said then that the heat loss of the house depends on the gap of temperature between the inside and the outside of a heat conduction coefficient , which will be noted "G". It also depends on the volume of the house, because the bigger the house is, the more surface is in contact with the environment. A shape factor should also be taken in consideration, because the less parallelepiped-shaped the house is, the more walls for the same volume. The shape whose the ratio volume/(wall surface) is the best is the shere. The cube isn't too far. Thus, this parameter will be ignored in what follows.
It can be written : Q = G × V × ΔT.
where Q quantity of energy lost (in Watt), G is the leakage coefficient (in Watt/°C/m3), V is the volume of the house (in m3) an ΔT is the gap of temperature between the inside and the outside (in Celsius degree).