There may well be some hints in the documentation, for example:
The heater is intended to be used for functionality diagnosis:
relative humidity drops upon rising temperature. The heater consumes
about 5.5mW and provides a temperature increase of about 0.5-1.5°C.
and for the SHT31 (link to manufacturer's datasheet, rather than some dubious site that accumulates datasheets of various ages.
4.10 Heater The SHT3x is equipped with an internal heater, which is meant for plausibility checking only. The temperature increase
achieved by the heater depends on various parameters and lies in the
range of a few degrees centigrade. It can be switched on and off by
command, see table below. The status is listed in the status register.
After a reset the heater is disabled (default condition)
In general if you don't find information in the datasheet that is adequate, look on the manufacturer's website for application notes, and for evaluation modules and the associated documentation.