The application will help to calculate the power of the heater required for heating the room, taking into account the desired temperature difference using the formula: V x T x k = kcal / hour, where:

V is the volume of the heated room;
T is the difference between the two air temperatures, outside and inside the room;
k is the coefficient of heat loss (or thermal insulation). It ranges from 4.0 (for buildings with very poor thermal insulation) to 0.6 (high thermal insulation).

And by the extended formula.

Heater power: Qt (kW / h) = (100 W / m2 * S (m2) * K1 * K2 * K3 * K4 * K5 * K6 * K7) / 1000