So, I had chilly fingers sitting in my tent watching the wasted heat shimmer away out the vent in the top of my Coleman tent.
And wishing and chilly imagined my Clay Chimnea (aka Mexican Chimney) radiating heat and how much better it worked than the olde fire-pit.

So...

Step 1: Look at the Wasted Heat

So, basic science...

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

Take a small clay pot and pass a bit of chain through the hole, clip it it the lantern hanger so that the pot is positioned just over the top of the lantern.

Step 3: Hang Low

Hang the pot and lantern lower than usual, the pot actually blocks some of the rising heat but it works better if it can radiate outward not down...

Step 4: Done.

Now you have a lantern / heater!

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.