And wishing and chilly imagined my Clay Chimnea (aka Mexican Chimney) radiating heat and how much better it worked than the olde fire-pit.
Step 1: Look at the Wasted Heat
Three flavors of heat Conduction, Convection and Radiant.
Conduction (touch) is The most efficient.
Convection is the heating of the air (no good here since it leaves too quickly.
Radiation... sticks around longer than convective current going thru the vent...
Step 2: Add Clay Pot
Step 3: Hang Low
Step 4: Done.
Don't expect miracles, it won't heat the house. And all the usual lantern in a tent warnings apply.
But it does use the waste heat fairly well, the pot is hot enough to evaporate a sprinkle of water in a few seconds, too hot to handle and will warm chilly fingers.
Warning though, these pots are fragile, if it's wet it may crack, but hey... DIY.