The reading on the balance when weighing a hot object compared to its weight at room temperature can primarily be affected by buoyancy. When an object is hot, it may heat the surrounding air, causing convection currents. This can lead to a slight increase in the buoyant force acting on the object and result in a lower reading on the balance compared to when it is at room temperature.
However, the effect may be very small for most standard weighing scenarios and would vary based on the object's temperature, size, and the specifics of the balance being used. In general, the reading will be slightly lower for the hot object due to the buoyant effect of the heated air.