In order to determine the temperature rise of a room due to an internal heat source, such as a kiln, you must do an energy balance and one or more heat transfer calculations.  The ASHRAE books will have some methodology for calculating heating/cooling requirements for rooms. However, they will be based on an energy balance and heat gain/loss from ambient.  The heat supplied by the kiln will be a combination of the hot air rising as well as some radiant heat from the walls and/or other contents. If the kiln is on temperature control, then the power input to the kiln will be the approximate heat gain to the room.  The room will not likely be at a uniform temperature in the short term.