My shop heater. It uses waste motor oil.
The heater housing is an inverted propane tank. I cut a door in the side and mounted a small cast iron frying pan approximately in the center, sitting on 1x1/8" steel fingers. I can remove the pan through the door to clean it.
Two turns of copper tubing wrap the top of the tank, then a "stinger" down to the inside to drip oil onto the pan. There is a piece of rubber fuel line running to a 5 gallon can of filtered waste engine oil. The metering valve is at the stinger, the hottest section of the pipe, where the temperature stays most constant and there's less fiddling to do.
Incoming air goes through the jacket on the flue; it gets plenty hot. It goes down the small pipe and into the side of the tank. After I made it, I added a piece of metal inside the tank to turn the incoming air 90 degrees so it swirls around inside; it helped keep incoming air from going up the flue without shedding some heat.
I was worried about the thing going out if left unattended, or flooding the floor with flaming oil. In the shop, it sits in a 6-gallon metal pan, so if the flame goes out and the frying pan overflows, oil will drop down through the hole in the propane valve and into the pan.
A 3/8" hole near the top lets me look directly at the fire without opening the door. This is about the minimum flue length you can use, but even so it runs at a net negative pressure, so no fumes escape from any joints, around the the door, or the peephole. With 10' of flue it draws so hard it makes sighing noises.
This was is the prototype. I picked 6" pipe because it was cheap and available. It's way too big, unless you're heating a barn. You have to have it burning high and hot to get a clean, smoke-free burn - and it *will* run smoke-free - but it won't do it below a certain point, far too high to be comfortable in my small shop. I recommend 3" black-painted vent pipe. If you use galvanized, you need to fire it up outside and burn the zinc off before bringing it inside. The zinc plate smells bad and will give you a nasty headache.
I don't think the combustion chamber size is of any real importance, at least compared to the flue size. I had several old-style propane tanks that cost more for new valves than just buying a whole new tank; they're thick steel and a convenient size. You could probably build one out of a coffee can and some muffler pipe.
I started off using a 5" muffin fan for forced ventilation, but it didn't need it. The internal 45-degree fins are to keep swirl going in the flue, the externals help radiate heat. You could probably skip them, but I had 40 feet of .020x1" angle I had no other use for, and some tin snips...
Ignition is easy - slide the pan out, put a wad of crumpled newspaper in, light it, slide it in, close the door, turn on the oil flow. You'll have to adjust the needle valve after a few minutes, when the copper coil gets good and warm. After a few hours when the oil tank warms up, you might need to adjust it again.
Like I said, it burns smoke-free if you keep the temp up. Turn the oil flow down and it doesn't burn hot enough to get rid of the smoke, and you'll be sending smoke signals to Mars. It's running about half wide open in the top picture.
I tried finding the upper heat limit and chickened out once parts started to glow red hot. I could turn the oil valve full-on, and it made a sound light a freight train, with shimmering exhaust going straight up in a twenty-foot column. I