The difference is the weight of the water that was evaporated from them. Multiply that weight in kg by 2,257 kJ/kg,[6] which is the heat of vaporization per kilogram, to obtain the number of kilojoules that went into evaporating the water, or multiply by 0.6250 kWh/kg to get kilowatt-hours. (Note: If the moisture later condenses inside the house, the latent heat will be converted back into ambient heat which could increase the temperature of the air in the room slightly.) [7] To obtain a good approximation of the effect this would have in a particular situation, the process can be traced on a psychrometric chart.