Convert a fire pit or old grill into a wood burning pool heater (water heater).
I bought a 16' x 4' pool, but found that a gas or electric heater would cost more than the price of the pool itself. I also had a lot of limbs and split wood from a fallen tree in my yard. This made for a very easy and effective combination. Now, when I burn wood in my fire pit, I also heat my pool.
Step 1: How it works
Cold pool water is pumped from the pool via the submersible pump into a 50 foot coil of copper pipe mounted above the fire inside the pit/ grill. By the time the water makes it out of the pipe, the fire has heated the water. This is similar to how a standard hot water heater works. The heated water exits the pipe back into the pool.