Home made wood stove.

[ken morgan]

this is basically an updated version of a fisher stove with a baffle and a reburn section added into the design, as well as a glass window in the side for aesthetics and ambiance. It is a little smaller on the outside than a Fisher "Momma Bear" due to the need to match to the japanese fire bricks (weird sizes) but internally it is only slightly larger than a "Baby Bear" due to the same issue (brick size). The bricks are basically 220 x 105 x 54 in mm or 8 3/5" x 4 1/10" x 2 1/10" so the interior dimensions are smaller than you would think.

The plate steel is thicker too as they the options were to go down in thickness from .25 to 6 mm which is .2362 or go up to 7 mm which is .2756 for the sides & bottom and as far as the top plates went, I arbitrarily went up from 5/16" .3125 to 10mm which is .3937, (just in case the reburn was more enthusiastic then expected).

The frames for the front and its door are all 8mm plate with a 5 mm bead welded to the plate to form the channels for the sealing gasket rope which also helps to keep the possibility of warping down. the same was done for the door with the viewing glass.

Just test fired it yesterday up at the cabin to heat the paint up and get the smell out of it prior to moving it into the cabin. With a 50/50 mix load of soft and hardwood it burned for right at about 4 hours with full heat output (600 degrees Fahrenheit measured with a IR gun on the bottom of the two plates) and 2 hours with just coals. that was with the primary air-feed and secondary air-feed (re-burn valves) wide open. I think that at the reduced levels and the re-burn set correctly it should burn for a full 8 or 9 hours.

one of my questions is does anybody have any idea on how large the re-burn holes should be? I drilled the holes with a 3.5mm bit so a little larger than 1/8" would 1/4" be better?

The water valves on the back control the secondary air (reburn).

Also the biggest problem so far is keeping the glass clean as i did not make an air wash system for the glass. A member of a chainsaw forum I am on suggested a top down wash right above the glass he thinks I could take the same 1"square pipe I used for the secondary burners and mount one above the glass with 1/8" or 1/4" holes and it should be sufficient, any thoughts on this?

Thoughts and critique are welcome.

 

[ken morgan]

 

[begreen]

Five tubes is a lot. How much air is coming into the secondary manifold and is it getting preheated? I would think that the sum of the area of the holes should be roughly equivalent to the ID of the manifold supplying the air. Following that thought, if the square stock 1" ID and the tubes are being fed on two sides then the area of the holes should equal about 2 sq in..

 

[ken morgan]

Five tubes is a lot. How much air is coming into the secondary manifold and is it getting preheated? I would think that the sum of the area of the holes should be roughly equivalent to the ID of the manifold supplying the air. Following that thought, if the square stock 1" ID and the tubes are being fed on two sides then the area of the holes should equal about 2 sq in..

actually the total area of the drilled holes is 2.8 square inches so its larger than the two inlet tubes which is two square inches exact. I figured the same but drilled extras in case some of them plugged between cleanings 260 total. the actual airflow on the secondary tubes is completely adjustable from 0 up to the full 2 square inches. if the holes themselves are fine then I will leave it alone and play with it to see what burns best.

one other thing I was concerned with is how will the air wash interact with the reburn? The air wash, if I fab one up, will only be like an inch or so below the re-burn, which in turn are 1.8 inches below the top of the stove sitting right at the bottom of the baffle. i guess I should probably make it adjustable also at least till I find the proper combo of air flow to burn for the stoves operations.

 

[begreen]

Sorry to say this but the air intake and smoke path flow look wrong. The primary air is being introduced at the wrong end, directly beneath the flue exit. It seems like that would cause the stove to burn strong at one end and not the other with little secondary action. Ideally you want the smoke path to be long and with the secondary air mixing as it travels to the flue exit over a baffle with the secondaries right below and mixing with the unburnt wood gases.

 

[ken morgan]

Sorry to say this but the air intake and smoke path flow look wrong. The primary air is being introduced at the wrong end, directly beneath the flue exit. It seems like that would cause the stove to burn strong at one end and not the other with little secondary action. Ideally you want the smoke path to be long and with the secondary air mixing as it travels to the flue exit over a baffle with the secondaries right below and mixing with the unburnt wood gases.
View attachment 200434

So you think it will waste fuel, or just burn slow?

 

[begreen]

Yes, it looks like as currently configured it will waste fuel and burn mostly on one end, near the air inlets. The air inlets need to be on the door end and the secondary manifold needs to be dropped below the flue outlet and have a stout baffle on top of it terminating a few inches from the door. You could probably drop one of the tubes in the secondary rack too. That should help a lot.

Take a look at the secondary conversions posted in this forum and the Fisher forum for some ideas.
https://www.hearth.com/talk/threads/grandma-bear-retrofit-with-secondary-air.140515/
https://www.hearth.com/talk/threads/secondary-air-conversion-of-old-stove.154832/

 

[begreen]

Here's a cross-section diagram of how most modern non-cat tube stoves are built. Old stoves can sometimes be adapted to mimic this design.

 

[Squirrely]

Thoughts and critique are welcome.

My first thought is to admire your creativity! You have considerable fabrication skills.

I can offer a suggestion for you to consider which might help. The holes in the secondary burn manifold on my Morso are aimed horizontally so the air flows parallel with the roof of the firebox rather than directly downward.



The air flows along the roof of the firebox towards the front door (south). Then air enters the top control disk...



...and through those two door glass air wash vents to direct the air downward parallel with the glass.



Then the angled louvers in the front bars deflect the air rearward (north) along the bottom of the firebox. The result is the burning gases flow around in a circle. You might try something similar with your manifold. Mine has a south-north circle because my firebox exit is on the south side at the front of the stove, so with a west exit you might try an east-west or west-east circle just to see what happens.

I love learning by direct first hand personal experience, and think it's really neat how you're exploring with your stove.

Greg

 

[ken morgan]

Yes, it looks like as currently configured it will waste fuel and burn mostly on one end, near the air inlets. The air inlets need to be on the door end and the secondary manifold needs to be dropped below the flue outlet and have a stout baffle on top of it terminating a few inches from the door. You could probably drop one of the tubes in the secondary rack too. That should help a lot.

Take a look at the secondary conversions posted in this forum and the Fisher forum for some ideas.
https://www.hearth.com/talk/threads/grandma-bear-retrofit-with-secondary-air.140515/
https://www.hearth.com/talk/threads/secondary-air-conversion-of-old-stove.154832/

Begreen what you are describing is exactly how mine is designed with the exception of the location of the primary air inlet. I understand that it might be hard to see in the photos but if you look you can see the baffle which is above the burn tubes and below the flue outlet

 

[ken morgan]

My first thought is I'm totally impressed with your creativity. You have considerable fabrication skills.

The holes in the secondary burn manifold on my Morso are directional and cause the flames to move in a south to north circle.


My first thought is to admire your creativity!

I can offer a suggestion for you to consider which might help. The holes in the secondary burn manifold on my Morso are aimed horizontally so the air flows parallel with the roof of the firebox rather than directly downward.

View attachment 200457

The air flows along the roof of the firebox towards the front door (south). Then air enters the top control disk...

View attachment 200459

...and through those two door glass air wash vents to direct the air downward parallel with the glass.

View attachment 200458

Then the angled vents in the front bars deflect the air rearward (north) along the bottom of the firebox. The result is the burning gases flow around in a circle. You might try something similar with your manifold. Mine has a south-north circle because my firebox exit is on the south side, so with a west exit you might try a west-east circle just to see what happens.

I love learning by direct first hand personal experience, and think it's really neat how you're exploring with your stove.

Greg

Thanks, this is my first time making a stove from scratch. and I am learning everyday playing with it. during the test fires the secondary re-burn section was burning as expected and the stack would go clean as soon as I open the valves. After a couple of burns I found that I could run the reburn at less than half open and get a clean burn. so I need to figure a way to get the air wash for the window but I don't want to add a lot more air into the mix just yet. I might pull the re-burn tubes and see if I can redirect some of it (maybe half?) through a air wash similar to what you were suggesting

 

[begreen]

Begreen what you are describing is exactly how mine is designed with the exception of the location of the primary air inlet. I understand that it might be hard to see in the photos but if you look you can see the baffle which is above the burn tubes and below the flue outlet

Good deal, sorry if I misled you. it's hard to see this in the photos. Is the baffle solid to the rear (or air control end) of the stove and a few inches back from the front (door) end? If so then it may work ok and the airwash becomes more of a design challenge. The airwash might end up being the main source of primary air in which case it will need a regulating mechanism. The airwash could be fed with 1" square stock forming an inverted U over the window. I would think a thin slit in the above the window area tube would provide the most even flow of air, but this may take some experimenting. Underneath the stove the two legs of the airwash would need to be joined and valved. A simple method might be to just box in an area, say 2" x 1" where the tubes open to the bottom of the stove and then put a spring tensioned blade valve whose lever extends to the front or glass side of the stove.

 

[Squirrely]

Thanks, this is my first time making a stove from scratch. and I am learning everyday playing with it. during the test fires the secondary re-burn section was burning as expected and the stack would go clean as soon as I open the valves. After a couple of burns I found that I could run the reburn at less than half open and get a clean burn. so I need to figure a way to get the air wash for the window but I don't want to add a lot more air into the mix just yet. I might pull the re-burn tubes and see if I can redirect some of it (maybe half?) through a air wash similar to what you were suggesting

The door glass air wash on our Squirrel is just two forty five degree downward angled 10 millmeter holes. However, all of the holes in the secondary burn manifold face towards the door rather than downwards. It's harder to get a tiny firebox to burn efficiently than it is for larger fireboxes. So I believe Morso's circular flow approach helps to overcome that handicap, although that design would likely help any stove regardless of size.

Let me know how your progress goes on the project, as this topic is totally fascinating. I'm certain you're getting a lot of personal satisfaction out of creating a stove from scratch. What you learn from your own experience always has value, because it can also be employed in other purposes..

I know a guy who started out needing a small stove for his trailer and ended up designing, manufacturing, and selling them. I have one of the new models he's getting ready to produce on backorder to put in our other home. It should be ready around November.

Greg

 

[bholler]

Looks like a pretty good well thought out build. One thing i didnt see mentioned and wanted to check because it could be a pretty big safety issue is what type of glass did you use?. As far as size of the holes i dont think it matters as much for you because you have complete control of the secondary air. You are just going to have to try it and see what works best. I also have doubts that you will be able to keep the glass clean because on the side like that it will have wood obstructing any airwash you install. Unless you have andirons of some sort to keep the wood away from the glass (which wouldnt be a bad idea anyway.

 

[bholler]

And when you install it make sure you have proper clearances to combustibles. For a stove like that it should be 36"

 

[coaly]

Hi Ken !
I wondered which direction you were going and I see you did well !
Opening an air wash to the atmosphere is going to prevent a lot of air from entering through the tubes. The path of least resistance would be directly into the front over glass, so with so many tubes you are going to loose the velocity coming in through the holes.
Also keep in mind the size of the holes determines the velocity of the air entering. If you open them up, thinking you can close the secondary intake, you are slowing the incoming air through larger ports. You want them small to make jets of air with higher velocity, not slow moving air through larger holes. Larger holes could require more chimney, plus your altitude has lower pressure to start with, so if it works with that size hole you better leave well enough alone.
Directing flame from holes pointed downward across the glass keeps the glass hot preventing condensing of vapor and clean. Normally the tubes are lengthwise with the glass and the front tube is close enough to direct heat over the glass. It should stay clean at least from the top down half way or more and only build up an accumulation at the bottom. Your burn tubes are very high and far from the glass where they need to be to direct flame toward it.

You need 6 inch clearance on the bottom unless going on a non-combustible floor or hearth.

What was your altitude again, so other commenters can take that into consideration?
I believe you could only get something like a 5 inch pipe and flue ?

Until tested with the chimney that will be used and cold temps, you're not getting a good indication of what kind of ignition you will have this winter. A sluggish burn or not lighting off much at all now may be great below freezing temps and really rip at 10* f. If you routinely see temps below -10 f, take that into consideration before trying to make it perfect now.

I did a calculation years ago of the hole size compared to square inch opening of intake of manufactured stoves at Lowe's. They all came up with quite a bit more square inch opening of holes compared to the area of intake opening.

 

[begreen]

And when you install it make sure you have proper clearances to combustibles. For a stove like that it should be 36"

With proper wall shielding this can be reduced to 12" in the US. Not sure what your minimum is in Japan.

 

[bholler]

With proper wall shielding this can be reduced to 12" in the US. Not sure what your minimum is in Japan.

Yes but 36 is the starting point

 

[ken morgan]

Good deal, sorry if I misled you. it's hard to see this in the photos. Is the baffle solid to the rear (or air control end) of the stove and a few inches back from the front (door) end? If so then it may work ok and the airwash becomes more of a design challenge. The airwash might end up being the main source of primary air in which case it will need a regulating mechanism. The airwash could be fed with 1" square stock forming an inverted U over the window. I would think a thin slit in the above the window area tube would provide the most even flow of air, but this may take some experimenting. Underneath the stove the two legs of the airwash would need to be joined and valved. A simple method might be to just box in an area, say 2" x 1" where the tubes open to the bottom of the stove and then put a spring tensioned blade valve whose lever extends to the front or glass side of the stove.
View attachment 200487

baffle goes from "rear" of stove location of air primary lnlets to within four inches of the front. fired it up this weekend will get into details below

 

[ken morgan]

Hi Ken !
I wondered which direction you were going and I see you did well !
Opening an air wash to the atmosphere is going to prevent a lot of air from entering through the tubes. The path of least resistance would be directly into the front over glass, so with so many tubes you are going to loose the velocity coming in through the holes.
Also keep in mind the size of the holes determines the velocity of the air entering. If you open them up, thinking you can close the secondary intake, you are slowing the incoming air through larger ports. You want them small to make jets of air with higher velocity, not slow moving air through larger holes. Larger holes could require more chimney, plus your altitude has lower pressure to start with, so if it works with that size hole you better leave well enough alone.
Directing flame from holes pointed downward across the glass keeps the glass hot preventing condensing of vapor and clean. Normally the tubes are lengthwise with the glass and the front tube is close enough to direct heat over the glass. It should stay clean at least from the top down half way or more and only build up an accumulation at the bottom. Your burn tubes are very high and far from the glass where they need to be to direct flame toward it.

You need 6 inch clearance on the bottom unless going on a non-combustible floor or hearth.

What was your altitude again, so other commenters can take that into consideration?
I believe you could only get something like a 5 inch pipe and flue ?

Until tested with the chimney that will be used and cold temps, you're not getting a good indication of what kind of ignition you will have this winter. A sluggish burn or not lighting off much at all now may be great below freezing temps and really rip at 10* f. If you routinely see temps below -10 f, take that into consideration before trying to make it perfect now.

I did a calculation years ago of the hole size compared to square inch opening of intake of manufactured stoves at Lowe's. They all came up with quite a bit more square inch opening of holes compared to the area of intake opening.

Thanks Coaly, you helped with a lot of information, I wish I could have read this post prior to installing this weekend We have no internet at the cabin, so I just got this data Monday AM my time at work.

So I installed it with the help of several young backs and hooked it up to my existing stack, (which I think is undersized but we will test) I am a firm believer in empirical testing on all things so this should be fun. I had earlier tested it in the shop using single walled 4" pipes that I ran up 16 feet.

prior to moving it to the house I drilled 6 1/4" holes in the secondary air tube to redirect air to the glass as an airwash as the tube is directly above the glass. This had the effect of (as Coaly suggested above) of killing velocity on the secondary air.

In the house the flue pipe is a double walled 4" stainless with a total of 20 feet length. Our elevation is 1100 meters (3500 ft) on the northern side of Mt. Fuji

The first load in the house was a batch of Oak, all properly seasoned but small splits, small length 14" (it was originally cut to match the old stove). I filled the stove in a NS orientation and lit it off and it burned from 2000 to 0700. on the slowest setting i could maintain a slow reburn at. Heat output was too high for this time of year and we had to open windows to adjust temp. I ended up closing the primaries almost completely and the air wash fed the fire (whoops!) but the glass was kept clean reburn was weak though, so I will plug two of the air wash holes and I need to close off some of the reburn holes and try again next week.

the stack temp was a little lower than I prefer, (IR gun at the only elbow in the system) only read 260 but when I went outside with a flashlight saturday night to check it the stove was burning really clean could not see any smoke at all so maybe its OK. I will monitor and check as I play and fine tune it. my old stove ran much higher stack temps, 350~450 at the same location, and same IR gun, but it had no reburn nor was it air tight.

so take aways from this experiment are Coaly's baffle ideas two thumbs up. My reburn circuit is too big, and I will end up welding shut about 1/4 of the holes, and I need to weld shut two of the air wash holes. once the above are done next week i can fire it up and test it out again.

the lower stove top plates average temp with reburn was 600 prior to going to bed. The upper plate was cruising along at 500ish when I woke up in the AM we still had fuel and it would have kept generating heat but I closed off all of the air inlets and the damper and killed it. It is hard to maintain reburn on such low settings, and that might be due to me drilling the airwash and losing signal on the reburn, or it might be too many holes in the reburn itself (260 1/8" holes)

for the guys asking about the glass, I ordered robax custom cut from the states, so no worries there. the space to my wall is only 16 inches, but I have a layer of 5/8" fire board that has a 1" air gap between itself and the wall, this is the same as I had last year with no issues. the base where the stove sits is a layer of 2.5 inch firebrick as the actual floor (?) it is the same as the firebrick in the stove itself. below that is a reinforced section of 4x4's to support he extra weight of the stove and whatnot.

 

[ken morgan]

Yes but 36 is the starting point

no established standards that I am aware of. not many folks use woodstoves here in japan. I ran the chimney flue and all myself last year and they sell the flue pipes at the local hardware stores so your guess is as good as mine. I just built mine as closely to US specs that I found online. I have a 5/8" layer of fireboard, with a 1" air gap between it and the wall and it worked fine last year...temps on wood behind the fire board never rose above 90 degrees so I am not that worried, though i will monitor it this year as its a new stove and its heat output is higher and different form the old stove.

 

[coaly]

Your IR reading on the outside of single wall pipe is about half the flue gas temp inside.
That 4 inch flue is like putting a 4 cylinder engine in a full size truck that needs a larger engine. On the flat and downhill you may be fine, but on a hill where horsepower is needed, your chimney won't have the capacity needed for a firebox that size. Of course if you keep it going and don't need the full BTU potential, you have a very efficient flow.

Your terminology is a little off discussing air wash.
Air wash is an air intake near the glass that air rushes in across the glass keeping smoke particles away. In a stove with only primary combustion, you start it with primary open, and go to only air wash when fire is stabilized. (you start to open primary a bit for more air when more heat is required, shortening the burn time of course) So "air wash" intake around glass would kill the secondary combustion more since the air flow directly in has no resistance, equalizing firebox pressure to the atmosphere stopping the forced flow through secondary opening. As you found out, the more openings the more it slows velocity coming in. You want velocity and turbulence to mix oxygen with flammable gasses and particles.

You'll find if you get good ignition now, you'll have a much stronger rolling burn with a larger temperature differential inside and outside of chimney. The flames will reach much farther down the glass the colder it gets. That's when you may need to turn down the incoming air.

 

[begreen]

Yes, I balked at the 4" flue. I wouldn't go smaller than 6" stove pipe connected to a proper insulated 6" chimney pipe.

 

[ken morgan]

Yes, I balked at the 4" flue. I wouldn't go smaller than 6" stove pipe connected to a proper insulated 6" chimney pipe.

yes I understand about the chimney pipe size, Coaly explained it to me last year. with the old stove it flowed well enough that the small stove would heat the house (actually overheat it a bit). That stoves drawback was its short burn time. at lowest setting with large (for it) pieces of hardwood I could not get much more than 2 hours of burn and an hour of coals, making me wake up every 2 hours or so to stoke the stove.

being that it flows enough to heat the house, the smaller pipe will keep the velocity in the stack up keeping the gases hotter longer and there for less creosote build up. it will however choke the stove down to whatever the 4'' can flow. so being that the flue pipes are only about 12 months old I will run them this winter with the new stove and decide if I need larger or not next winter. they are double walled and the pipes run inside the house until the exit from the roof with about 4 feet above the roof line. regardless at best I can only run a 5" anyway due to space constraints.

when I made the stove, I made it for a 5'' flue pipe and then made a cone adapter that dropped down to the Japanese 106mm pipe that I currently have. if I need to go with a 120mm (5'') then I can pull the adapter off and run a the 5'' pipe instead. hope I don't need to as I paid about 1300.00 for the existing pipe parts and if I replace it it will be another 1300.00 so next year at the earliest and only if I need it.

the main reason I built this was because to buy a stove here locally in Japan of comparable quality, burn time and capacity would have cost me about 5k for just the stove uninstalled. not having that I built this one on a budget of about 600 for steel, glass and fire bricks. If I can avoid replacing the flue that would be great, if I cannot then I will get it next year.

 

[sportbikerider78]

These guys know more than me so I know when to shut up.

Very nice fab skills! I can appreciate how much work went into that.