This is how I converted an old propane grill into a wood fired grill and smoker. It doesn't take much for tools or materials and can be completed in an afternoon. The wood chamber was inspired by a few rocket stoves and gasifier I saw on this site.
Step 1: Buy Materials.
1x 8in black pipe slip joint
1x 6in black pipe slip joint
1x 6in black pipe cap
2x 6in black pipe collars
1x furnace cement in caulk tube
1x HVAC rain cap, 6in
1x 2ft section HVAC pipe, 5in
1x 2ft section HVAC pipe, 4in
Firebrick, lava rock, large stones (optional)
Step 2: Fabricate Metal Pieces for the Wood Chamber
You will need to drill a total of 24 3/4"-1" holes. It shouldn't matter too much what size the holes are, and measuring and lining them up are not crucial. On the outer shell (8" black pipe) you will need to drill 8 holes on the side without the "slip" connection. This will be the bottom of the unit. Go slow when drilling these out. I used a spade bit (4 of them to be exact, because they wore down after about 6 total holes each). Next the inner shell (6" black pipe) needs to be drilled at the top and bottom. Fit you cap onto the non slip joint side and place your holes above the lip, this will be the bottom of the inside. Place the top set of holes below the lip of the slip joint ring.
Tips for drilling the holes:
clamp a 2x4 in a bench vise and put your pipe over it for drilling. This will make is so you don't crush the pipe while exerting downward force from drilling.
It's easy to eyeball the placement of the holes if you drill one hole, turn the pipe so that hole is at the bottom, drill another, and turn them so they are at the side and drill again top and bottom. Then just estimate halfway between each of the 4 holes you have already made for the last 4. Or... If you are so inclined, spend an hr measuring them all out...
Now you are ready to measure out the inside hole. I'm using a 5" pipe because I want to easily be able to feed in 2x4 scraps from my shop (not for cooking...). I suggest cutting the 5" pipe to contour the 8" pipe first. When that is completed place it on the side of the 8" pipe and trace around it. Cut this hole first before you measure or cut the 6inch hole. You will want to make it slightly smaller that the 5" pipe and slit the metal every half inch or so with sheers to make little wings.
Cut the 5" pipe to match the contour of the 6" pipe on one end, and leave about 10-12" total length.
I also made a damper for the infeed hole out of a end cap. I slit the edges and bent them out and then a second time back in so that kinda clamps around the hole.
You will need to cut a hole in the bottom of the grill the size of the 4" starting collar.
The rain cap needs to have a 4" diameter hole cut into it. Measure the length from the rain cap (when sitting on top of fire chamber) to the bottom of the grill and add 1/2-3/4". Make slits around one side either 1/2" or 3/4".
Step 3: Assembly
...test fit all parts before using any furnace cement...
Attach the 6" cap to the side without the "slip" joint of the 6" pipe. Seal this with furnace cement.
Slide the collar over the end of the 6" pipe with the slip joint that you pre slit. The collar should rest on the lip of the slip joint. Bend the tabs down to hold in place. Seal underside with furnace cement.
Place the 6" pipe inside the 8" pipe with the holes on the 8" pipe on the bottom.
Insert the 5" infeed pipe through the 8" pipe and into the 6" pipe. Fold in tabs to lock in place. This should be a snug fit. Seal outside with furnace cement. Folding in the tabs on the inside is a good place to get cut, so wear gloves and be carefull.
Fire chamber is done.
Connecting to the grill:
Insert the 4" pipe into the 4" hole on the rain cap. Slit side in. Fold in the tabs on inside.
Insert starting collar into hole on bottom of grill.
Fold in tabs.
Attach 4" pipe (with rain cap at bottom) to starting collar.
Attaching to grill is done.
Inside the grill:
This instruct able assumes you have an old grill that has been gutted.
I used fire bricks on the inside to help hold in heat, as well as to block any ash that might come up through the vent. If height temps are needed in the grill this also works well to put wood chunks in.
Some may choose to fill the grill with lava rock. That would work too. Haven't tried it may self.
I also made a mesh piece to go on the inside of the fire chamber to keep the coals off the bottom. Look at the pics for assembly.
Done with assembly.
Step 4: Operation
Before using to cook you need to burn off all the galvanization. To do this get it as hot as you can. The damper cap may need to be burned in a fire pit as it will not get hot enough.
I have found that a fire starter with a few split logs (I prefer hickory) about 1 1/2" wide works well to get it going. It's ok if the fuel sticks out a little. As it burns down push the logs in further and add as necessary. If you want a lot of smoke soak a few logs and add them after the first batch of dry logs has burned into a nice bed of coals.
I will at times add large logs under the fire bricks to create a lot more smoke and heat.