Hot tub question

Hi, I have a Laurel Mountain Whirpool hot tub. I want to add an in line heater for it, but all the heaters I see online just maintain the current water temp. I am looking for a heater that has a keypad for adjusting the temp. Anyone have any ideas? Thanks

heater

That would require a larger unit than would fit "inline", so you may just have to run the piping through a conventional heater