This heater is a combination of concepts from the article describing the Roger Sanders drip-fed oil heater unit (here) and concepts and components from my double bowl wood stove burner insert discussion (here), and my defunct attempt at using an antique oil-o-matic furnace burner for heat (discussion here).
I salvaged the base and burner tank from the oil-o-matic heater project as the starting point for this heater. The sanders heater used an electric water heater as the burner tank, I am using a 100 pound propane tank, it is a bit smaller than the water heater but has proven to be plenty big enough for my small 750 foot small house.
Initially I intended to use the double burner concept but found that this burner did not burn reliably with fuel levels that are less than about a quart per hour, This much heat in my small house had the wall thermometer pegged at its max of 100 deg f in a couple hours of use, woke me up swetting something fierce, had to come up with something that did not put out as much heat but was simple to impliment, settled on using a simple readily available stainless steel camping store 6 inch diameter mixing bowl as the burner.
This picture is of the heater as I first built it. The base and burner tank are reworked from the earlier oil-o-matic heater, the burner bowls were the next step in the double bowl burner concept.
The base for this burner is made by using one of the shallow bowl shaped disc cutting blades from a farm cultivator. This disk is 18 inches in diameter, the propane burner tank is 14 1/2 inches in diameter, I welded a 2 inch tall steel band to the top of the disk (bulge up), this band allows the propane tank to just slip inside it, the band is welded to the disk such that the weld is liquid tight, this keeps any excess fuel from dripping haphazerdly from any place around the band. These disks are made of very hard steel, too hard to make holes using standard drill bits, I heated a one inch area of the disk red hot just where the disk and band meet, Then drove a tapered punch through the red hot area, this made a 1/4 inch diameter funnel shaped hole, this allows any liquid to drip from this one location, A drip container is placed below this opening.
The oil-o-matic burner unit originally went through a 4 1/2 inch hole in the center of the disk, I made an insert to fill this hole and also to be the mounting base for the lower burner bowl. The lower bowl was made from a 10 inch diameter center section of another 16 inch disk blade, this 10 inch bowl is only 1/2 inch deep so does not hold much fuel, only a problem at cold startup, need more fuel than it holds to get everything hot when starting up cold.
This picture is of the disk base, the center hole insert, and the lower 10 inch bowl. The insert simply sets through the large hole, the piece of 3/4 inch pipe on the bottom of the lower bowl then drops over the 3/4 inch rod welded in the center of the hole insert. This allows everything to easilly be disassembled for cleaning, put a bag under the big center hole and the soot in the bottom of the burner tank is easily swept out through this center hole.
This is the rear view of the burner tank on the base. The round opening is where the combustion air tube goes, I designed this to allow the combustion tube to easily be removed for ttesting or modification. This burner tank was from the oil-o-matic heater originally, I had welded the 6 inch flue outlet directly in the top center of the tank so had to go about getting the combustion air inlet from someplace else. I also wanted to prove to myself that the combustion air tube did not have to be an absolutely straight shot from the outside to the top of the flame.
This is a closer view of the air inlet tube opening. This shows a piece of 3 1/2 inch pipe welded to the tank as the air inlet tube mounting point, the actual air inlet tube is made from 3 inch pipe, the 3 inch ID air inlet pipe slips through this opening and is clamped in place by the 3 bolts shown, this allows positioning the air inlet tube in about every direction possible.
This shows the actual air inlet tube leaning against the burner tank in about the position it has inside the tank. I went with 2 45 degree bends rather than one 90 degree because it made it easier to fit the 1/4 inch steel fuel feed line inside, also gave a bit easier path for the air flow.
This shows the air control valve clamped on the end of the combustion air tube. Notice the 3/8 inch hole about an inch down inside the air tube, this is for a 90 deg brass fitting. the fuel comes up a piece of 1/4 inch steel brake line along the outside back of the heater to this fitting, then through the side of the air tube, then runs back and down the air tube to terminate 4 inches above the bottom end of the air tube.
My wood stove double bowl burner air tube has the fuel tube 3 inches from the end and it will get covered with a bit of carbon and crud over a couple weeks, so far 4 inches has worked with no problem.
This is a picture of the lower end of the fuel feed tube. It is a 1/4 inch steel brakeline tube that has a 1 inch length of 3/16 steel brake tube brazed in the end, Sanders indicated that 1/4 inch tube by itself makes too large of a fuel droplet, the 3/16 tube has an 1/8 inch ID and has worked well so far. I also brazed a 1/4 inch ss bolt to this end of the tube, this bolt goes through a hole in the side of the combustion air tube and fastenes thisend of the fuel feed tube securely in place. I did not do this on the wood stove burner and that fuel feed tube shifts around a bit with changes in heat, makes it miss the fuel shoot on the double bowl burner some times.
This picture shows the position of the original concept double bowls through the open door of the burner tank. these bowls work well if you need the heat they provide burning a quart of fuel/hr or more.
This picture shows a veriation on the double bowl burner, the hope was that the thin lower bowl being isolated away from the heat robbing heavy steel lower bowl would allow the double bowls to work at fuel feeds less than a quart/hr, sorta worked but the bowls kept moving somehow, the upper bowl would shift enough that one of it's legs would drop down inside the lower bowl, this would cause the upper bowls fuel to spill into the lower bowl causing the upper bowl to mostly go out. There was something about this idea that caused the bowls to shift, may have been warping of the thin lower bowl as the heat changed or it may have been outgassing from the new fire brick under the lower bowl, don't know, I did hear "popping" or "bumping" coming from the burn chamber each time the bowls shifted ? This could be researched further but I shifted over to using the very simple insulated single bowl burner, this single bowl has workes so well with even vary small amounts of fuel, down to less than a half pint/hr, that I have not done any more testing with a double bowl in this heater.
This picture shows the above modified double bowls burning in the heater, when the door is closed they burn more vigorously because of the center-supplied combustion air. I think the fuel rate for this burn was .22 G/H, this thin isolated bowl concept probably would burn less fuel once the problem of the bowls shifting position was figured out but I never tried it.
This picture is of the 2 pieces making up the single bowl burner. One is a $7.00 SS coffee grounds kitchen canister that I found at wallmart. This is 5 inches in diameter and 5 inches tall, it is needed for a couple reasons, it gets the actual burning bowl up close enough to the air inlet tube and it also insulates the lower 2/3 of the burner bowl from the cool combustion air that is moving around in the burner chamber. By insulating and isolating the lower portion of the burner bowl from the cooling air it stays hotter and thus vaporizes even small amounts of fuel. The white stuff inside the canister is plain old fiberglass house insulation, helps hold heat in the burner bowl. The Burner bowl itself was found at a camping store. It was called a 6 inch SS mixing bowl, simple thin china-made stamped bowl with the edges turned under to eliminate sharp edges, cost under two bucks, I have a couple and simply swap out cruddy for clean every couple days, stove never even cools off much. It does take about a half hour from the time the fuel feed is turned off til the fire is completely out in a crudded-up bowl.
The bowl shown here is typical of a 48 hour continuous burn at a fuel rate of about .20 G/H. The crud in the bowl is mostly soft ash, very little, if any, actual coal. I clean the bowl in under a minute using only a pocket knife.
This is a top view of a crudded up bowl that burnt for 72 hours continuous, this is a day too long without cleaning. You can see how the ash sort of crusted over the top of the bowl area, this reduces the air to the fire and causes more smoke to be produced. I did not notice any loss in heat but definatly caused more smoke.