I use an Avantco 3500 for strike water/boil kettle, and picked up this Duxtop 1800W unit for $49 for heating sparge water while mashing. No problem heating 3-5 gallons of sparge water to 170-180 during mash time.
https://www.amazon.com/gp/product/B0045QEPYM/?tag=skimlinks_replacement-20