heat loss calculation

A window glass with a height of 0.8 m, a width of 1.5 m, a thickness of 8 mm and a thermal conductivity of k = 0.78 W / m2K
consider it.  It is desired to keep the room temperature at 20 0C when the outdoor temperature is -100C.the units of transmission and convection coefficients in question have Kelvin, whereas interior, exterior and surface
  temperatures are given in 0C (degrees Celsius). First, write the relationship between 0C and Kelvin.
  Then search for a calculation error here? does unit conversion required?