The rate of heat loss from the inside of a building to the outside, through a particular element such as a window, wall or roof, is called the U-value of that element. It is measured in Watts per square metre (of window, wall etc) per degree Kelvin difference between inside and outside temperatures.
By calculating for all the elements, the overall total heat loss in Watts can be determined, so that you would then know how much heat you need to inject to maintain a reasonable inside temperature.
I should add that in addition to heat loss through physical elements, there is the need to replace the air in the building so that the inhabitants don't suffocate. The incoming air to replace the warm inside air needs to be heated and the required number of Watts can be calculated and added to the previously calvculated sum.
I'm not aware of an overall coefficient for the whole house.