As part of a physics project on energy and efficiency my class was instructed to build stoves out of cans and other recycled metals and attempt to heat up water with as much efficiency as possible. Here is the procedure to build my bum stove, for all the homeless people out there with access to the internet, or for any hipsters who think building your own stove out of recycled metals makes you better than everyone else.

Step 1: Materials (All Sizes Are Approximate)

1 large can (substantially larger than a soup can)
1 smaller can that can fit inside the largest can (a bit larger than a soup can)
1 even smaller can that can fit inside the second largest can (about the size of a cambell's soup can)
1 metal tube about 6 inches long and 1.5 inches in diameter
1 piece of wire mesh large enough to cover the bottom of the largest can
1 pair of tin snips for snipping tin
1 drill
some caulk
wood chips or wood pellets
two flat rocks
1 can opener

Step 2: Largest Can

First cut the top off the largest can with a can opener
then cut 4 small tabs equidistant from one another around the rim of the now open end of the can. Fold these inward, they will insure that when you place the lid back on the can it won't fall in.
next cut a hole in the side of the can just large enough for two-inch-wide tube to fit into. Make sure the hole is as close to the bottom of the can as possible.
On the bottom of the can, drill a bunch of holes so the fire can ignite the pellets (it will make more sense later)

Step 3: Second Largest Can

Cut both the top and bottom of the second largest can off with a can opener.
cut a hole in the side of the second largest can that is the same size as the one you cut in the largest can.

Step 4: Smallest Can

Cut the top of the smallest can off with a can opener
Cut a multitude of small tabs around the rim of the open end of the smallest can, and fold them outward like in the picture above. Don't cut them too deep because you want to maximize the amount of water the can can hold, the cuts should be about an inch deep.

Step 5: Assembly

Start by placing the wire mesh in the bottom of the largest can
Next, place the second largest can inside the largest can, making sure the holes in each of them are aligned with one another.
slide the six-inch-long, two-inch-wide, metal tube into both the holes. Make sure that the tube barely enters the inside of the inner can. You want to leave enough space in the second largest can for the smallest can to fit into.
apply caulk around where the tube meets the hole on the outside of the largest can, this will insure that the tube doesn't move out of place.
place the smallest can within the second largest can using the out-folded tabs to suspend the bottom of the smallest can from reaching the bottom of the can it sits within.
Place the lid on the top and boom! your stove is complete

Step 6: How to Use

prop the stove up on the two flat rocks leaving a space between the rocks. Place paper and other ignition materials in the gap between the two rocks, directly beneath the stove.
fill the smallest can with however much water you wish to heat and place it in the second largest can.
Toss wood pellets, wood chips, or whatever you plan on using as fuel into the metal tube so that it ends up beneath the can with water in it.
Light the ignition material so that it will in turn ignite the fuel.
Place what you would like to cook in the water and put the lid on the stove.
Enjoy!