No need for separate equipment for sparge heating. Even though I have a Robobrew instead of GF, this is what I do.
Fill up Robobrew to brim, heat to 82 degrees then transfer about 18l to my 20l drink style esky (you know the ones with the tap at the bottom). That leaves about 13l left in the Robobrew where I top up to desired mash level. Usually only have to add between 5 to 7 litres. The temp then drops to around desired mash of 66. If not heat up a little or let sit and cool a little. So much quicker and uses a bit less energy.