First let’s check whether Spotlight is the cause of the fans running so much. To test this, run the following in your terminal:

sudo mdutil -a -i off

This will turn off indexing of files, and should result in a clear slow down of the fans if mds and/or mds_stores are to blame.

To turn indexing back on, run

sudo mdutil -a -i on

After this you could run the complete re-indexing of your hard drive (be aware this could be an over night job), it will delete your Spotlight data base forcing it to start over.

sudo rm -rf /System/Volumes/Data/.Spotlight-V100/*