Kerosene will only start evaporating once it's being burned in the kerosene heater and will not evaporate just from hot weather.
For kerosene to begin evaporating the temperature would have to be around 150 F to 170 F or higher which is around the temperature that the heater begins to burn the kerosene.
The kerosene heater uses a wick to suck up the kerosene which then gets burned off or evaporated in the burning of the kerosene to produce heat.
But kerosene doesn't evaporate during storage so it lasts a long time in storage and doesn't go bad like gasoline does and kerosene also does not freeze like gasoline can in really cold temperatures.