Introduction: Pellet Fed Rocket Stove
Rocket Stoves, combined with Wood Pellets for fuel are an excellent match. Rocket stoves were invented in the early 1980s and were originally developed as a solution to reducing deforestation in third world nations that consumed wood for cooking and heating. Their clean burning nature also helps reduce health problems from inhalation of smoke and carbon monoxide associated with poor combustion from traditional open fire pits. Today, Rocket Stoves are the answer to anyone, anywhere wishing to reduce dependence on fossil fuels and central power distribution to heat their home. Properly designed, Rocket Stoves require no external power to operate and can run constantly with only occasional ash removal as maintenance. No moving parts to wear out means years of dependable service. Further additions of copper piping can distill water or be the source for a hydronic heating unit. Add an additional flat plate of steel and cook your daily meals using Sustainable fuels like wood pellets or other forms of biomass can add to your fuel diversity. Connection to a Stirling Engine linked to an alternator can generate electricity and charge a battery bank as an added bonus and icing on the cake for any Homestead!
It is time to become energy independent and Rocket Stoves appears to be a part of this plan!
Rocket stoves like to run hot and as a result they burn clean. Add a fuel with a consistent heat density delivered in small pellets, it is possible to have a small stove generate a lot of heat with a small footprint. Rocket Stoves are efficient and wood pellets are a Sustainable Resource; a win - win right from the get go! Using relatively inexpensive construction materials, one can build a pellet stove that efficiently heats a room and can continue to heat the room using it's "banked heat" long after the stove has burned the last pellet in the hopper.
After many hours of sifting through what seemed to be every version of a rocket stove on the internet, I got tons of ideas on what my stove needed to do.
It needed to:
1) Be Safe. Safety with fire is always paramount. I also wanted to keep most of the high heat area out of the reach of children as this stove would be in a kitchen / living room open concept. So the decision to make the body of the stove out of Refractory Cement. The cement does get hot to the touch but not like the side of a conventional steel wood stove. Also, an added benefit of the cement is that it slowly radiates heat for hours after the stove is off.
2) Be Small. By Small I mean economically heat a 650 square foot area and do so with a constant output. I did not want large temperature swings, so a small 2" x 2" firebox. Most pellet stoves are designed for over 1300 square feet and that is twice the stove capacity that I needed. The other small is small footprint. The base of this rocket stove is 12" x 12" and utilises vertical space to it's advantage; using 5' of vertical space and one square foot on the floor.
3) Be the Curiosity Focal Point in the room; OR at least, Be a topic of conversation in a warm environment! Yes, there was an Executive Order (from my wife) that the Stove be painted Pink!
4) Be economical. Original design consideration was for the stove to run from 8am to 8pm. Shutdown each night. Clean out of ash box each morning. A 40 lb. bag of pellets sells locally for around $8 Cdn. This stove burns a pound an hour ; so operating costs is $2.40 per day of comfortable, eco-friendly, sustainable heat. Not a single dinosaur was hurt, except for the transport of the bags of pellets from the big box store to home.
5) Be easy to install. Pellet Stoves can be vented straight out a wall with 3" insulated pipe and a 4' Rise.
I chose to go with a design that started with the smallest metal burner that could hold a pellet basket and manage to handle the largest advertised pellet length of 40mm. Then a cast refractory cement body for safety and the thermal mass component. Finally a 30 lb modified propane cylinder to be the Heat Bell before exiting a 3" insulated flange to outside exhaust stack.
I am grateful for my wife for her faith and patience in the development of this rather unique method of heating our home. My gift to her. I also wish to gift this design to the approximately one billion people on this planet that still rely of biomass for cooking and heating their homes. I also gift this stove design to anyone wishing to strive to a more sustainable carbon - neutral fuel resource.
Step 1: Introducing ..... Franken Stove: My Pellet Fed Mini Thermal Mass Heater Rocket Stove!
Here is my version of what I call "Franken Stove". Although the Rocket Stove and Pellet feed hopper are easily recognisable, a fabrication style that has hints of Steampunk Design giving it the aura that this item may have been pulled out of an Industrial setting. Here is a YouTube link of the stove in action: www.youtube.com/watch?v=KpnZwKVNzbQ. If the link does not work, try a search using the title: Pellet Fed Rocket Stove / Rocket Mass Heater- “Franken-Stove”. Here you will see a video explaining the finer design parameters. Oh, and by the way, I did get that wall receptacle cover installed! Thanks for your concern.
To achieve this look I chose to combine metal fabrication for the burner, hopper and Heat Bell but with a casting of refractory cement to make up the Cubic base of the Heater. By using Refractory cement for the body of the stove you are given the benefit of having a small thermal mass that radiates heat for hours after the stove is shut down. By continuing with refractory up into the Heat Bell the advantage of added thermal mass is obvious and an added safety measure of preventing direct contact to the hot metal pipe riser.It operates in the 250 to 300* C range, consuming approx. 500g of wood pellets an hour. It requires no electricity to operate and pellets are gravity fed from an 8 hour burntime capable hopper. It heats 650 square feet comfortably. Requires minimal supervision. Five minute cleanout in the morning is a snap and it starts up using a propane torch.
The design as described is currently operating in the 200* to 300* C range ( at Sensor location on stove). Temperatures at the top of the Heat Bell rarely exceed 250* C This is to be expected as this is directly above where the flame exits the insulated metal riser. Less than a cup of ash and unburned pellets are left in the ash bin and less than a half in the Fly Ash Jar, each morning. I also incorporated an auxilary atmospheric steam supply right behind the pellet feeder which improves combustion . This stove is preheated with a propane torch and usually takes 3 to 5 minutes to start by slowly adding pellets after the preheat. Stove usually reaches operational temperatures within 30 minutes. Air adjustment for flame optimization is by two simple metal baffles allowing air to enter the Primary (Combustion) and Secondary Air Chambers. The final ash glass, located immediately below the riser is vented with two 1/8" holes drilled in the Mason Jar; it appears to help reduce downdrafts, aid in final combustion of any particulate and keep Bell Temperatures under 550*F Indicated . It also serves as the initial preheat point for the first 2-3 minutes. I have found that preheating the riser first expedites the draft process. Usually, by the time I have the Final Ash Glass cleaned out and ready to replace for startup, the Indicated temperature is around 100*F and there is enough draft to redirect the propane torch to the Primary Combustion Tube to continue to adding pellets for the next stage of the light up process. This startup process cuts back on back draft smoke during light up.
Step 2: The Tools for This Trade!
Flux core Welder, 4.5” grinders, drill press, impact gun, wrenches, table saw, metal cut off saw, squares, levels, pipe wrench and ratchet straps.
Step 3: The Treasure Hunt!
30 lb Empty and de-valved propane cylinder (Heat Bell) NOTE: Find an Instructable on how to safely do it!
10 lb Empty and de-valved propane cylinder ( Hopper)
3" Muffler Pipe approx 32' (Riser)
Portland Cement, Bentonite Clay, Perlite, Silica (Refractory Cement Components)
Threaded Rod 3/8" bolts and washers - to hold cast body together and act as attachment points for add - ons
3' of 2.5" x 2.5" thick wall square tubing.
1.5" Flat bar - Band around the Heat Bell and part of the Burn Tray
Melamine sheet - This is the outside mold of the Cement Section.
1/2" black pipe - These are the spacers and ribs of the Refractory Cement Section of the Stove.
BBQ grill (Pellet Burn Tray)
Angle Brackets (Secure Riser to Black Pipe)
Angle Iron (Stand and Hopper Alignment)
Sheet Metal ( Air Adjustment for Combustion and Secondary )
thermo gauge. Laser Digital Thermometer - better for accurately measuring the heat profile versus one point!
1.5" styrofoam sheet - to fabricate the combustion tube to the Riser
Aluminum Duct Tape - to hold styrofoam sheet together.
Hot Melt Glue Gun - to secure the styrofoam form to the base of the Stove
Trowels - to work the cement into all the crevises in the mold
1/2" copper pipe and fittings. solder flux and solder, sand cloth - to make the afterburner / Steam Reformer
Propane torch, Mason Jar and Screw lid, Old BBQ grill for burner basket, BBQ temp gauge
High Temp Paint
Pellet Stove Exhaust Kit ( buy at Big Box Store (insulated 3" pipe))
Step 4: Acknowledgements Those Who Built Rocket Stoves Before Me.
There is a plethora of designs of Rocket Stoves and I am sure that everyone posted has served its purpose to some level of success that the original builder has desired. This speaks well of the overall design of rocket stoves in general and I have found that it is possible to glean a little knowledge from each and every builder / designer that has had the courage and determination to face the world and display their efforts on an open forum. As I write this list I am certain that I may have missed acknowledgement so if you see an idea of yours in my build, please contact me and I will be sure to give credit where credit is due. I have included a short 3:26 minute video on the overall operation of "Franken-Stove" here as many have questions on heat profiles and the travel path of the combustion gases.
I sourced mainly YouTube for most of my research on Rocket Stoves because I wanted to see how they worked. I also wanted to experience the builders point of view, how he operated his heat machine and any ideas on what he felt in his opinion made his design work better than others. I personally, have difficulty reading reams of information and retaining it. Visually, however, I have the ability to process and piece things together better. That is why I have included a video of Franken-Stove in operation so others like myself can get a better idea. I am writing an Instructable because, I feel, that I can convey more details all in one place to help save anyone else who wishes to build Their Version of a Franken-Stove. Here is my YouTube video: www.youtube.com/watch?v=KpnZwKVNzbQ
So, I wish to acknowledge the following YouTube contributors:
T2H - for giving an excellent overall view of how Rocket Stoves work and his ideas on swirling the combustion gas and the need for more oxygen addition after the pellet combustion chamber.
David s - for showing how a rocket stove can be made from square tubing on its own. Also for providing the valuable insight on having the combustion chamber ratio of 3 times the length of the combustion tube diameter. For example, The combustion tube of Franken-Stove is a 2"x2" square opening. The length of the combustion chamber after the edge of the pellet inlet tube is approx 6" before the gases hit the "T" to travel up the Riser.
Stressedout 72 - This gentleman demonstrated how to build the refractory core of Franken-Stove. I regret not heeding his recommendation for the drying time required for this type of cement in colder temperatures.
Step 5: Heavy Lifting - the Building of the Thermal Mass Block Box
The Refractory form for this project measures 12" x 12" x 12". Melamine makes a good form as it acts a mold release when the cement mixture is dry and set.
On the Front Face cut a 2.5" x 2.5" square hole that will fit the Fire tube. Also drill 4 holes in each corner for the addition of 1/2" black pipe spacers and threaded rod. Drill additional holes for the Burner Tube mounting bolts. Weld rebar to each black pipe to give the refractory strength and to affix the Riser Tube for strength and security.
Take 1.5" styrofoam sheet and cut 3" wide strips. These strips are used to make the square channel way Tee that allows for an ash bucket below the Fire Tube ( this is a secondary ash trap to catch fly ash) and the draftway into the metal 3" pipe riser above. The part of the Tee that fits into Burner Tube will need to be shaved down a bit and the corners rounded to fit into the 3' riser pipe. Fix the pieces of styrofoam using aluminium duct tape. This will burn away during the first burn of the stove. Hint: for a faster initial burn out, Dado out a 1/2" channel way and make the burn out from the top of the riser down. The styrofoam will become it's own feed fuel and the 1" x 1" hole in the styrofoam will be the supply air. This will also slowly preheat the Refractory which is the best way to initiate a burn to condition this material for higher temperatures. It is difficult to see this relatively small but important part of the build but if you look closely, you should be able to see it in the pics.The second pic from the left shows the best angle. Observant viewers will notice the old 45 degree incline on the first fab of the pellet tube feed on the original burner assembly. A steeper, more vertical feet tube was retrofitted as pellets hung up too much on the lower incline.
Insert the Burner tube into the mold, fit the styrofoam Tee into the Burner Tube and hot melt the secondary clean out end of the Tee to the melamine base.
The Mold is now ready for the Big Pour. Dry Mix a equal amount of: Portland Cement, Silica Sand, Perlite and Bentonite Clay. Add water and mix to a wet sloppy consistency using a drill and cement mixer attachment. As the area is quite busy with reinforcing rods, styrofoam channel ways and metal riser, it will be necessary to use thin rods to poke the refractory mixture all around to float in the mix. It is easier to do this with a sloppy mix but one must allow more time for drying and setting.
Pour in wet mix and float in the mixture all around the metal bars and be careful not to contact the styrofoam Tee as this may dislodge it from its contacts and the work will be lost. Pour to top of box and let sit. Be patient as it may take a few DAYS to set and dry. If you do not let it dry the the work will crack on first firing and you will be left with a lesson on patience the hard way. I was guilty of this on my first stove; Learn from my impatience, unless you wish to make two stoves!
Step 6: Modifications.
Modifications are normal in the build design process. Here are two worthy of mention on this build.
Modification 1. Steam Reformer to Afterburner.
By attaching a 500 ml Stainless Steel water bottle to the Burner Assembly, it was possible to heat water via conduction to boiling. By allowing this steam to super heat as it is drawn into the Afterburner, a better burn pattern was observed by looking down the Heat Bell. Burn Temperature stabilised to 550*F and the throat of the pellet basket appeared to stay clear of ash. This idea came about from a video of a rice husk rocket stove using water / steam injection to improve combustion. A photo of the Steam Reformer can be seen above. As it is in tangential contact with the outside of the combustion tube, the water in the stainless steel bottle gently boils and is drawn up into the copper pipe and into the afterburner inlet. The water generally last as long as the pellets in the hopper. This happened more by chance than design. It’s better to be luckier than good I guess! There are also two photos of the flame pattern that show the difference with the addition of steam to the afterburner. The photo with steam addition is a bright ball of orange -white flame whereas the photo with the orange tounged flames is just air entering the afterburner inlet. It may seem counterintuitive that Steam aids in combustion but that is all part of combustion chemistry.
Modification 2. Pellet Feed Tube Angle.
The Pellet Feed Tube angle was modified to allow for a more vertical pellet feed. The angle of the pellet feed is 22.5* off vertical and an ash tube was then incorporated to have better Secondary Air Flow and a larger ash compartment.
Modification 3. Pellet Basket.
Pellet Baskets are important to bring Pellets, heat and Oxygen all together so you get an efficient burn. It is necessary to have a simple design to allow the pellets to fall, burn and decrease in their size and ultimately fall into the ash box. This is very difficult to do in a 2" x 2" square metal tube. It is here where the most revisions and trial and tribulations took place. The only suggestion I have for you here is to build two identical pellet baskets and slowly modify one at a time and observe the results.
Modification 4. Secondary Ash Container.
I really wanted to observe what was going on in the Heat Riser. The original way to watch was to look down the 3/4" NPT plug on the top of the Heat Bell, but doing so hot gas would rise up and into the room and was inconvenient as I would have to climb up a step latter every time I wanted to make an observation. By Installing a glass secondary ash container directly under the Heat Riser, I managed to solve three problems with one modification: 1) I could catch light ash that would end up in the Heat Bell. 2) I could get a reflection of the flame travelling up the Heat Riser. 3) By drilling 3 small holes in the glass with a diamond drill, I could add a little more air and have it preheated exactly where it was needed. This also appeared to prevent down draft puffs of smoke. Another unrelated benefit of the Secondary Ash Container is that it gives a better start preheat inlet as it is necessary to use a propane flame to start these Rocket stoves.
As mentioned earlier, I am attempting to keep this instructable a living document. The last chapter has been added to show some of the “ final “ mods that has upped the performance of this stove above and beyond expectations. Please read thru to the end as it will help in the design of your stove!
Step 7: Building the Burner Tube Assembly- Weld 'Em and Grind!
The Burner Tube Assembly consists of:
1) Combustion Chamber also known as the Primary Air Inlet - This is the horizontal tube where wood pellets fall into and burn in an intensely hot chamber
2) Ash Container which doubles as the Secondary Air Inlet - Directly below the Combustion Chamber there is a hole where ash and small pellet embers fall thru the Pellet Burn Tray. Secondary Air travels up thru this ash and ember pile; continuing to burn what is left and supplying hot additional oxygen to the burning pellets
3) Pellet Feed Tube - Pellets feed via gravity down this to find their way into the Pellet Burn Tray.
4) Pellet Burn Tray - This holds the burning masses of pellets until they are small enough to fall thru and end up in the Ash Container. The design of the Pellet Burn Tray will probably be the most difficult task to get right as it is here where everything comes together for an efficient burn. Pellets must fall freely into the basket and not get hung up in the Feed Tube. They also must not crash down and choke the throat of the Combustion Chamber. Yet the embers that fall thru the Burn Tray cannot choke the Secondary Air Inlet either. I spent many hours and many Burn Tray configurations before I came up with the reliable design that I am now using. I still have a few other designs I'd like to try but it ain't broke yet so I will write an Instructable instead!
5) Afterburner Air Inlet - I found that there was a need for even more air required to efficiently burn the pellets. Many designs I viewed cut a slit behind the Pellet Feed Tube to allow more air past the Pellet Burn Tray. However, if the slit was too large, wisps of smoke would push out during a start up or on exceptionally gusty days where a sudden downdraft would temporarily reverse flow. To solve this problem I drilled two 1/8” holes in the fly ash jar and have noticed no wisps of smoke after this revision. I suspect that this additional air is required to burn the pellets that are experiencing pyrolysis just above the pellets in the Burn Tray. That is why I call it an Afterburner Air Inlet; you are adding superheated air ( or as I now use: superheated steam) to unburned fuel behind a combustion chamber (just like fighter jets ( but less glamorous and a lot slower and quieter)). Mounting Bar - Secures the Burner Tube Assembly to the Thermal Mass Base.
Cut pieces of Square Tubing on a Metal Saw. This makes for pieces fitting together and welding together better. Some cuts will have to be made with a hand grinder. Ensure that there is nothing for the pellets to get hung up on as they transition from the Feed Tube to the Pellet Tray.
As mentioned earlier, the Pellet Burn Tray is the most difficult part of the build as it is here where everything comes together; Fire, Air, Fuel. The spacing of the Pellet Tray has to be made such that there is a balance as to what will fall thru and when. Many designs of Pellet Fed Rocket Stoves fail at this stage. There is an art to these designs; I have found a design that works on a 4 square inch fire face. It may not work on any other size fire. Another consideration is the material kind of material to fabricate this Tray. Due to extreme heat in the Fire Zone, I found that BBQ grates work well and can be welded reasonably well if you grind off the porcelian coatings. The grates I found were triangular and have held together well thru many heat cycles. I also found that perforated stainless steel can be used in the design to slow the fall thru rate of the pellets and help direct airflow in this critical area. Refer to Pictures of Burn Tray. The Burn Tray has small spacers on it's base to allow combustion air to travel under the burning pellets.The Burn Tray sits directly over the Secondary Air Inlet and the feet of the Burn Tray straddle this opening. Sliding the Burn Tray slightly forward decreases feed rate of pellets and lowers burn rate and operational temperature slightly.
I chose to add superheated steam to the afterburner inlet because at high temperatures the steam dissociates to H H O and reacts with any unreacted carbon in the exhaust stream. Also I am denying the addition or nitrogen that is present in the air from entering the combustion chamber. This lowers the risk of producing Notrogen Oxides or NOx gases.
Step 8: Sub - Assemblies: Pellet Basket, Afterburner, Spy Glass, Fly Ash Containment
Here, I will talk about four of the unique pieces of Franken-Stove that come together to make this stove work so well.
1) Pellet Tray- The Pellet Tray is a very important component of the Rocket Stove. It is here where Fuel, Heat and Oxygen all come together for the Combustion Dance. The Pellet tray must fit inside the Combustion Tube with close tolerances so it can slide forward into the Combustion Tube and slide backward for removal and cleaning. This forward and aft movement over the Secondary Air Tube give some adjustment to the Rate of Combustion and ultimately the Indicated Temperature and overall Performance of the Rocket Stove. The fingers of the Pellet Tray are made from high Temp BBQ grills. Spacing is wide enough to let pellets drop into the Vee but not too wide for them to fall straight down into the Secondary Air / Ash box. Many versions were tried to get to this balance right and let the small embers fall thru. I strongly recommending building several and experiment with them and modify one thing at a time and see if it gives an improved result. The pellet basket above works well with long wood pellets. It tends to allow small pellets to fall thru and clog up the Secondary Air / Primary Ash Containment. You may need to build several Pellet Trays to work with different brands of wood pellets. All wood pellets are not created the same. It is here where I found the need to have a visual as to what was going on so I designed the next unique part.
2) The Spy Glass- The Spy Glass is a Magnifying Glass wrapped with a Bike chain and mounted to the Primary Burner Tube. It gives the operator the ability to watch what is going on in the Pellet Basket where Combustion is taking place. The chain gets warm to the touch but is manageable as the glass is hotter. Being able to see the fire is a welcome option with Rocket Stoves as the burn chamber is usually hidden behind a metal door in almost every design I have seen.
3) The Afterburner Assembly- As the wood pellets experience the extreme heat in the pellet tray, they begin to pyrolize and disintegrate into gases. By adding an opening to allow heated combustion air (or steam) downstream of the pellet basket, hot oxygen rich combustion air is introduced and allowed to combust any unburned material as it travels up the riser. This makes for a hotter flame an a cleaner burn. By positioning the inlet of the afterburner near the inlet of the Secondary Air, smoky downdrafts are prevented and the air is allowed to be heated by thermal radiation from the hot metal burner. Measurements from an Infrared Digital Thermometer have observed over 100 degrees F increase over the inlet air. The Afterburner is now piped to an Atmospheric Steam Generator which improves combustion and provides HHO into the high temp region which facilitates a cleaner burn.
4) Fly Ash Jar - Located directly under the Riser, the Fly Ash Jar preformes three tasks. First, the Jar catches any ash or embers that are too heavy to travel up the Riser. Second, it adds a small amount of cooling air (small 1/8" hole drilled in glass jar, see pic) to travel up the Riser and keep a strong draft continuing up the riser. Finally, it gives a reflected view of the flame travelling up the Riser. A small stainless steel cup prevents embers from resting directly on glass to prevent cracking. The Jar is threaded to it's metal ring which is secured to the base of refractory cement using cement screws and high temperature silicone.The metal ring is crimped to the flat sheet metal that is secured to the cement base to allow for threading and unthreading. The 3" x 3" hole is a result of the styrofoam "T" cast in the firebox during the cement addition.
Step 9: Suggestions for an Even Better Franken-Stove
It has been just over 24 hours since I posted this Ible and have already had over 2k views! I’m Honored that there are so many of you out there that have an interest in my creation. Once again, at 9238 views! I have made some changes to this Instructable, mainly the addition of the problematic original video and some dimensions a few steps below at the end.
I have a few suggestions for those who wish to make one for themselves....
1) Go Vertical!
It is worth an extra cubic foot of refractory cement as the heat dissipation will last longer and you can do the whole pour at once.
Because...... my vertical refractory column is just slightly off vertical. I also had to do a second pour for the lower part of the 30 lb Heat Bell
2) Make it your Own! Ceramic tiles pre mounted (inside the form) will bond nicely to the Portland cement in the mix.
Invest in a diamond 1”boring bit and pass the support rods thru the whole mold to prevent it from bursting apart under the weight of the refractory.
A boring bit can be found for under $20 at any decent hardware store. Absolutely worth it!
Because..... glazed ceramic accepts heat resistant paint readily and the tiles you choose add a personal touch!
3) Don’t fight Gravity!
Engineer your pellet feeder to drop pellets vertical. Everything in this stove gets hot eventually and if there is something that gets included in these wood pellets while they are being manufactured ( like a piece of plastic) it may fuse to the surface and begin the log jam. (Which shuts down your Toasty paradise. )
And Because....the increased length of the Primary Combustion Chamber will also improve the combustion characteristics. I read somewhere (but forgot where) that the length of the combustion tube should be at least three times the diameter of the combustion opening. ( I seem to remember a gentleman on YouTube by the name of David S referring to this ratio)
4) Let’s get Flexible!
The bolt-on nature of the Burner Assembly allows for different fuel sources. Designing a Burner Assembly to accept small pieces of scrap wood like construction waste and old pallets
adds another dimension to frugal heating.
5) The Dreaded Angle of Repose!
I waited a long time to get the perfect picture of pellets finding their magic Angle of Repose where the wood pellets found a way not to go down the Pellet Feed Tube. Any particulate material has its characteristic angle of repose and it appears to be around 45 degrees for wood pellets. I would recommend building rectangular pellet hoppers that had sides at 45 degrees to prevent this from happening.
New Note: I have posted a video of the Franken-Stove operational with the Steam Reformer Addition. Enjoy!
Please go to the YouTube video listed above to get a full picture of how this particular Rocket Stove operates. ?
Please subscribe for more up until contest close. Peace and be warm.
Step 10: Dollars and Sense! the Bottom Line!
The Labour of Love is Free. Given the basic tools listed and knowledge of welding this is a worthy project that should last for years with next to no maintenance.
Take your time... save even more!
Measure Twice; Cut Once ...$Priceless
Wear your PPE!
$12 Portland cement
$12 Bentonite Clay (cheap cat litter)
$25 muffler pipe 3” (3’ bought from muffler shop
$25 heavy wall square tube
$00 old expired propane tanks
$20 threaded rod, nuts washers.
LESS than $150 CDN - and I think that it can even be built for less!
$0.20 CDN per Hour! Given a 40 lb. bag of wood pellets are $8.00 CDN with Tax
Are there any off-gridders out there? ??
The Sense: There is something very comforting from wood heat. There is also something to be said for being warm in your own home and not fretting over how fast that wheel is spinning on the electrical meter or gas meter or the bill from the oil truck. Not to mention the Service bill for a furnace to repair it in the middle of winter. We live in an area where winter storms wreak havoc with our electrical utility and we are now a little more prepared!
Step 11: Burner Assembly Dimensions
Here are photos of the Burner Assembly and Associated Parts. The measuring tape is blurry in one photo but it is possible to get the overall idea on the construction of the parts in question.
I have included three pics of my light up procedure so you can get an idea how "Franken-Stove" gets fired up in short order. First, I remove the Glass Ash Container at the bottom of the Stove. I insert the lit torch in the vertical Heat Riser and heat until the temperature reaches 100*F. At this point the Heat Bell is "heat primed" an a light draft is created to the outside. Second I place my "kindling" (egg carton, wood pellets, melted wax) into the Secondary Air compartment and light it with the torch that has been moved from the vertical riser. ( the glass Ash container is obvious in place at this time). Once the kindling is burning well, the torch is then moved to the Primary Air / Combustion chamber and wood pellets are slowly introduced down the pellet feed tube. Stove reaches steady state temperature of 450* to 500* F Indicated on the Heat Bell. The far right pic shows the wood pellets introduced and the torch removed from the Primary Combustion chamber.
NOTE: You will notice that the spyglass is shattered. Yes... I did that on purpose. I was not sure if it was a tempered lens or if there was even such an animal. I did not want to have it explode in my face so I touched it with a wet rag when it was hot and the stove was running. The result is observed that it was not tempered and the crack relieved a lot of stress in the glass so I no longer worry about exploding glass shrapnel. I think it gives a little character to the design as an afterthought! :)
Although this is a Rocket Stove, one should not feel that they have to be a Rocket Scientist to build your own. I am treating this Instructable as a living document and I am adding tidbits of information as I receive feedback from subscribers and I appreciate anything that will positively help at improving the build or design. The Rocket Stove I have built has been fairly forgiving in dimensions as long as the welds hold! About the only advice I have on building the burner is to make sure it is build on a flat plane so it does not look crooked when you look at it.I have included a sketch with some dimensions on it If you are going to use dimensions use the photos with the measuring tapes on them. You will get better ratios. And more accurate measurements.
Step 12: All That Thermal Energy and Where It Goes
I took the time to try and observe what was going on with respect to where the heat was going as a function of the Indicated Temperature ( That spring temperature gauge above the Owl's Head) versus various key positions on "Franken-Stove".
On the day of measurement of all this data, the weather here was very erratic; which probably explains how Franken-Stove managed to have a 425*F to 525*F temperature swing throughout the day. Extreme gusts of wind and equally erratic direction accompanied with heavy rain downpour probably was not a good day for data collection to find temperature profile nuances but here are the numbers listed anyways in the above photos.
The temperatures were taken with an infra red thermal measuring device with a laser pointer that can be bought at any decent tool store. When measuring the temp I selected max temp mode and took the highest temp of two scans of the area in question.
The temperatures were measured from beginning of the wood pellet drop thru to the final exhaust out the chimney. The weather wasn't constant and probably skewed the results and statisticians will say that there are not enough data points but I will try to draw some conclusions based not only on these numbers but from the near constant monitoring I have been doing on this creation since I bought my temperature measuring device.
So what I interpret from this data is:
1) Temperatures in the pellet feed tube are generally constant so there is no heat build up and the pellets probably experience a bit of drying as the descend down the pellet feed tube.
2) The largest swings in temperature are where the Primary Air and Pellet Feed intersect. Of course, this is where the Combustion Dance begins and continues to give off energy as it passes into the Refractory Cement Mass.
3) The side ceramic tiles seem to level off around 170*F which leads me to believe that the Refractory has a finite heat bank of energy and then manages to "push the remaining heat" up into the 3" metal Heat Riser.
4) There is a correspondence between T(indicated) and the Heat Bell radius. Both rise 100*F
5) The spyglass temp seems to be constant once steady state is achieved.
6) The exit temperature out of the Heat Bell appears to be constant, averaging approx. 300*F
7) Exhaust temperatures rise as T(indicated) rises.
The basic conclusion I can make from observing this Rocket Stove in action is that it appears to find it's own "Happy Place" somewhere 450 and 500*F. There are many variables as pellet size and manufacturer and mixing the pellets has been far from homogeneous. I have reason to believe that mixing long pellets and small pellets makes for a better combustion mix to allow combustion air to find voids and react better than consistent sized pellets but that will take an entire season to truly figure out.
I once heard someone mention that you can manipulate numbers to say whatever you want them to say but what I have tried to do here is show that you can take a small amount of wood pellets and combine them in a small area with an appropriate amount of oxygen (and Steam) and generate an incredible amount of focused thermal energy. By combining Heat Resistant Materials (Refractory Cement) with Heat Conducting Materials (Steel) and changing the direction of the Flame you can capture a large amount of energy and transmit it in the form of infra red radiation which heats your environment in a very comfortable and efficient manner. I continue to marvel that this type of stove can heat a living room / kitchen open concept are using about a pound of wood pellets an hour and it does so without electricity and very little maintenance and no moving parts.
In conclusion, what I can say about "Franken-Stove" is that it works! Once lit and it breaks thru the 450*F Indicated Temperature zone the Stove just runs and all you hear is the slight rocket hum and the low boil of the Reformer Steam to the Afterburner. Consumption rates of wood pellets remains relatively constant as the hopper needs to be filled once after original top up during start and the occasional clearing of ash build up in the Primary Air Inlet. I am overwhelmed with the interest in this project and I wish anyone whom attempts this project the same success with it as I am having. I also would like to Thank the Instructables Team for their support with answers on how to write this, my first Instructable. Thank you and good luck with your build.
Step 13: The Final Add-ons!
In celebration of over 10k, visits to see my Franken-Stove and those of you that appreciated its design to favorite it, I wish to show you the final details that has saved me hundreds of dollars on my electrical heating bill since December.
I will discuss the photos above in order from left to right.
The first photo gives an overview of what the Burner Assembly looks like with Add-ons of a refitted ash drop and stainless steel ash pot and expanded water reservoir with red dye indicator, a new glass burner window and secondary internal pellet returner with a “Steam Reformer Snorkel”
Photo 2 demonstrates the addition of a water reservoir that is a Repurposed water bottle for pets. I removed the stainless steel tube and replaced it with an old CPVC toilet water supply tube that is inserted into the original stainless 750 ml water container ( the stainless water bottle has 4 stainless scrubbing pads stuffed inside to make small rolling bubbles of steam as opposed to over boiling the water. I added a few drops of food coloring for effect and so I could see the water level from a distance. The coloring only need to be added once as it does not boil off and bubbles back into the upper reservoir by thermal siphoning.
Photo 3 shows the repiping of the Steam Reformer Snorkel to Feed superheated Steam to both the Afterburner ( behind the Primary Combustion Chamber ) and above the Ash Container ( in the Ash Chute). This modification was in response to ash clogging up my original ash container / Secondary air addition as I found I would have to empty hot ashes “on the fly” so optimal air could be supplied to the Secondary Air directly under the Primary Combustion. This mod allowed the stove to run untouched for hours on end. It also significantly reduced ash generated by further burning the small embers that fell thru the pellet basket during normal operation. The larger capacity of the stainless steel container allowed for once a day emptying with next to no black coke / coal in the morning clean out. In other words and more simply, I built a smaller rocket stove under the original Combustor. I can not understate the importance of including steam addition to your design. By adding steam to the combustion process, you are reducing the amount of nitrogen present which for all intents and purposes does nothing for the combustion process in generating heat. Oddly, it appears that this design to have a “moist throat while the fire feeds on the relatively dry (6% moisture max) wood pellets. Similiar to us enjoying water to drink as we eat!
Photo 4 shows the new spyglass that is a Repurposed flower holder that has openings for combustion air to enter the Combustion Inlet. The old spyglass hindered and perhaps choked down air addition. The new spy glass has tapered holes that focus streams of combustion air into the glowing red hot pellets which is akin to a forge. Furthermore, ash is blown away from the throat of the pellet basket where the ash then falls down the ash chute into the ash pot. Also, in this photo it can bee seen how Springs were used to hold the lid to the pot. Another final performance tweak to get Secondary Air to where it is needed, one can see the air tube which extends into the Ash chute to provide air directly up to the base of the Combustion Chamber.
The final photo shows an exploded view of the Ash Catcher / Secondary Air / Ember Combustor. Yes this stainless container is now a second rocket stove that takes care of the small embers that fall thru from the Primary combustion chamber. A steamer base is used to help the keep the small embers suspended so Air / Steam can further react and burn the ember during operation and for some time after shutdown. This gives even more heat on the back end after the pellet Feed has dropped its last pellet into the Primary Combustor.
So, there you have it! A gravity pellet Fed Rocket Stove Thermal Mass Heater that burns clean and takes care of heating your space safely and no moving parts.
Stay tuned for a water heater mod using copper pipe and another application of thermal siphoning.
Thank you to all that took the time to read my I’ble to completion. I encourage you to build one of your own and marvel how it works at freeing you up from the needless complexity of current pellet stove technology
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