3 Ton WaterFurnace Envision. This homeowner installed an underground drainfield based on our input. Supply water is again from the domestic well (open loop). After running through the WaterFurnace, the water is injected into the drainfield ~ 5ft below the surface where it drains back into the ground. This is an effective and inexpensive way to discharge water with an open loop system. Performance depends on soil type in the area.