I have searched for information for a ratio or some standard size to base a home built furnace body combustion chamber in relation to burner size. So far I have either been overlooking or not looking in the right place if the information is out there. Does anyone have a good ratio for chamber volume per given amount of BTU/HR or any other standard… most can be pretty easily converted from one format to another… Basically I am attempting to work some bugs out of the WVO burner I have been working on for the past month. My attempts so far were using thick walled 3” and 4” pipe, both were about 4′ lengths.

The burns using this setup both met with flames the length of the 4′ pipes, some smoke initially till the pipe walls heated up then a clean burn with the flames extending about 3′ down the pipe at a burn rate of 1/3 gph. My plans are to build and try a different size/shape combustion chamber than the pipe has offered to see if the flame outs will decrease. Any input is welcomed and Hopefully that will help point out something I have overlooked so far in the setup I have tried. The application I have planned for the burner is in firing my homemade smelting blast furnace initially , and after gaining faith in the design being reliable and stable enough incorporating it in to our existing natural gas home furnace and water heater. Thanks in advance for any insight offered.

If you use a narrow 4” pipe to burn through, the flame touches the pipe. Result: incomplete combustion and lots of carbon on the pipe inside. If your furnace construction allows it, I would make an extension as wide as the combustion chamber is. The length of the extension depends on your burner. Once you have set the burner, you know the ideal flame length. It is important that the flame does not touch anything. Not even the target at the end of the chamber. Cover the extension inside with fire brick. I added a wide pipe made of very thin stainless steel to burn through. Otherwise you get no recirculation of combustion gases in a long chamber. Recirculation results in a very clean burn.

Can you please elaborate on the “wide pipe made of very thin stainless steel to burn through.” I am trying to picture the configuration, what size original chamber, what size extension, and what size and length of pipe and the placement, and the recirc path of gases, and why you needed the pipe.

Some statistics: original burner chamber size: deep: 25” + target, wide: 21”, high: 25”. It’s a rectangular chamber; can also be used to burn coal in. Extention size: deep 10”, wide: 11”, high: 17”. I extended the doorframe 10”. Have a look in the photosection at Dutch John’s burner. Flamepipe size: Diameter 9”, long: 11”, sheet thickness: .02”. I used 300 series stainless steel. This thin because it heats up fast. The reason I made the door extention was to allow the flame its “natural” long length. If it hits the target, emissions will go up. Now the fingers of the flame stay a few inches before the fire brick target. I have some oil droplets escaping sideways from the flame. These droplets wettened the extention inside and vapourated after burner shutdown. The wide pipe generates a hot gas flowback between extention and the pipe. This recirculated gas enters the pipe at the root of the flame, catches the oil droplets and is “afterburned”. I see it this way: it is not only building a siphon burner to burn heavy oil successful. You also have to adapt the boiler/furnace.

The only guidelines that I have found were a minimum of 80 square inches of floor area of the combustion per gallon/hr of fireing rate but that is with HHO. The recommendation was also for the chamber to be about 1” longer than it was wide and the height to be a little more than the width. With a siphon nozzle, that would not get a long enough combustion chamber for the flame. As a minimum, I would think that the chamber for a siphon nozzle should be sized for at least 50% higher firing rate than what you are firing at with the siphon nozzle. e.g., a 1gph siphon burner would need to have a chamber at least as big as a 1.5gph HHO pressure nozzle. That is what the commercial waste oil burner manufacturers do. The flame should not touch the combustion chamber at all, especially the sides.