Worry about the hot water melting the plastic hose. Plus, fumes and smoke from the fire can soil the air for the swimmers.
Snip from website:
By combining a fire with a water pump, there is now a constant stream of heated water flowing into this backyard swimming pool. The theory seems sound, and hopefully this doesn’t just look like it works but it actually does heat the water.
Yeah… so, this is something we recommend our readers not do, unless you don’t mind accidentally burning the side of your above-ground pool and causing all of the water to gush out. Instead of investing in a pool heater like any non-engineer would do, this person decided to reroute their pool pump to pass over a crude BBQ pit to bring the water up to temp.