My dad did something like this once. He built a serpentine pipe apperatus
for the fire place .  Then built a fire on top of it.Kinda like a log
rack.He connected it to the furnace pump and pumped hot water  through the
house heating system. Sounded good.The fire heated the water and the water
heated the house.In theory.

The pipes exploded.Pressure got real high real quick.There was no pressure
relief and no expansion tank.It sounds like lots of plumbing connections
to me.Get a pocket warmer.