Service host encompasses other windows services that are running on your machine, so it's normal. You can disable other apps or startup items from within task manager, and possibly run a malwarebytes scan to ensure you don't have any junk on your system.
It's possible the fan is just running because you need to clean out the vent with compressed air. I suggest downloading CoreTemp and testing your CPU for any signs of overheating if the fan consistently runs more than it used to.
also, you can go into power options in control panel, and check to see if you are on the "high Performance" profile. This will run the computer in active cooling mode. If so switch to balanced and see if the fan slows down.