Yone' Ward wrote:If you put your RMH under your pool, you will have no way to regulate how much heat you are putting into your pool. It will be very easy to cook your fish accidentally as there will be a significant time delay between when you light the fire and when the heat gets to the water and if your water is getting too hot, there would be no way to shut off the heating.
However, if you use a masonry bell type RMH, wrap it in insulation, and run pex tubing between the insulation and your heater and then under the pool, then you can transfer the heat to the pool with water that can be thermostatically shut off when your pool gets too hot. If your RMH is below (not under) the pool, and you take care how you run your pipe, then gravity will pump your hot water for you and won't circulate the water if your RMH is colder than your pool.