Fresh out of the brain of eernest4 , with no outline on paper, before hand, because that is way too much work for me to do,thank you. So if I ramble just a bit,please bear with me. Long read, but long on info, too.

This is a lengthy project, so should be done in the late spring,summer or early fall when you wont need to lite off your stove. ************
btw &fyi;, THESE MODIFICATIONS, are not for new stoves, but for 1960 & 1970 & 1980 smoking dragon stoves
that are way out of warranty, warranty expired. Any stove that still has a warranty, do not do this modification because they will void your warranty, for sure, even if the stove repairman gives you a compliment for a job well done. Stoves built 1990 & later do not need this as it is already designed into a 1990 or newer stove, unelse you bought a vorgizelanger el cheapo stove. (if you own one,you know what i mean) The V word.

A NOTE ABOUT THE FIREBOX SIZE. These modifications are easier done & with better results on large to extra large size stoves. The stove I did had a 12 cubic foot firebox, big enough that I could get my whole upper body inside it & work laying down on my back , with my legs sticking out the stove door. If you have fairly good access to the insides of your stove without becoming a contorshionist , then go for it. But if you have a small to medium sized stove,heats 1000 to 1400 sq ft. dont bother with it, because it will be harder to do because of tight space & restricted access to the inside of the firebox & the results ,for a small stove , arn’t really worth all that effort.
It is a different story when it is designed into the stove, at the factory, before the stove top is welded on.

My stove was eating a cord to 1.5 cords a week, now I go a month on 1.5 cords to 2 cords, so for me , I went from not having enough wood for the winter,to having wood left over for next winter.

The whole point is ,more heat,less wood,less smoke. A small stove uses less wood to start with & therefore can’t do an overnight burn, so many of the benifits of secondary burn are lost with a small to med sized stove. But,if you are inclined , please, be my guest & dig right in.

WHY GO TO SECONDARY BURN CONVERSION???
TWO MAIN REASONS
1. GET 40% MORE HEAT FROM YOUR STOVE USING 40% TO 60% LESS WOOD TO DO SO.
This means less time cutting & splitting & drying wood & less wood to buy & less wood you need to burn during a heating season. THIS CAN CUT THE MONEY YOU SPEND ON WOOD FOR A HEATING SEASON IN HALF.

a PRE epa 1970 STOVE (airtights) & others, Can at best delever 30% efficency, some pooly designed models, only 20 % to 25 % & the rest of the heat goes up the chimney as smoke.

Most secondary burn EPA Certified stoves were made from 1990 on. Before 1990,stoves were only 20% to 30 % efficient instead of 72% to 84% efficient.

SMOKE IS UNBURNED WOOD FUEL that can be burned to give more heat inside your stove & not released up the chimney as wasted fuel.

You know you have a good secondary burn going when the stove top temp is 550-650 deg & the black stove pipe temp , measured at 18 inch above the stove is 400 deg. & this is what secondary burn is all about; the stove gets hotter than the stove pipe.

2. The other reason to have secondary burn is NO SMOKE UP THE CHIMNEY. You don’t smoke out or polute the neighborhood.

You know your secondary burn is going when all you see out the chimney is clear heat shimmers.

Now our homemade conversion is not going to be 84% efficient or even 72% efficient like a stove designed by engineers with degrees and custom built for secondary burn, but we can some times & usually, hit the 40 % to 60% efficency range without any problem. Every stove is different to start with & I offer you no guarantees as your results will vary. I am happy with the way my stove turned out , I think it is running at 50% efficiency, up from 25 %. I know it emits less smoke now & more heat for less wood. In fact, I cut my wood usage in half.
SECONDARY AIR PIPES::
One mistake i made was not to drill enough holes in the secondary air pipes. Holes should be 3/16 inch drill bit ,spaced 1 air hole every inch of pipe that is inside the stove.

On my initial attempt, I got the 3/16th diameter right but only put the air holes one every 6 inches. I still got secondary burn , but not when i wanted to, instead,only when the stove felt like it.

In order to assure secondary burn on every fire, secondary air holes need to be 1 or 2 inchs apart down the entire interior
length of the secondary burn air feed pipe.

Most stoves will require 4 secondary burn air feed pipes , going from 1 side wall 3/4 to 7/8 of the way to the other side wall & monted 1/4 of the way from the back wall, then in the middle of the stove ,then 3/4 of the way from the back wall & the last one about 6 inchs before the baffle plate entrance to the secondary air chamber.

SPECIAL NOTE FOR STOVE WITH GLASS IN THE DOOR: Glass door stoves must stop the baffle plate & first secondary air supply pipe well away from the glass to make sure no flames impinge (touch or come too close to )
the glass. we don’t want to shatter your door glass because the baffle plate & entrance toi the secondary burn smoke chamber & secondary burn air supply tube are too close to your door glass. SO PLEASE KEEP THIS IN MIND WHEN YOU LAY OUT YOUR STOVE MODIFICATION PLAN. **********************************
i ALMOST FORGET TO TELL YOU THAT the first pipe come from(note #1) one side wall of the stove & stop 3/4 to 7/8 of the way from the opposite side wall with a end cap to close off the end of the pipe. This will force the suction inside the stove from the stove pipe, to suck by vacuum , the preheated secondary air out of the little 3/16th holes that you drilled in the sides of the pipe. THE HOLES IN THE PIPES SHOULD FACE DOWNWARDS TOWARD THE FIRE. It is not critical if they are on a little bit of an angle, just generally downwards towards the wood.

FOOTNOTE#1, ABOVE:
the second pipe comes out of the opposite wall of the first pipe; the pipes are staggered , 2 out of one wall & two out of the other, so there will be a even distribution of secondary burning air throughout the interior of the stove.
right wall pipe,left wall pipe,right wall pipe,left wall pipe.

Pipes can be (1 of 2 methods,see below) mounted to the stove wall by drilling a hole through the stove wall, starting with a 1/8 in drill & working up to the diameter of the pipe thread. Here you will need a pipe thread tap & tap handle , so that you can screw the pipe into the stove wall for a smoke proof ,air tight seal. A high temp pipe thread compound or even retort cement on the pipe threads can be used.

FOOTNOTE; IF YOU HAVE THE PLUMBING SUPPLY HOUSE THREAD THE END OF THE PIPE AN EXTRA INCH OR TWO LONGER & the tap threads allow you to screw the pipe in far enough before it tightens up the pipe too much to turn, you may be able to thread a old water valve on the end of the pipe so you can use the water valve as a secondary air adjustment control, if you find that you need to adjust secondary air. SEE ALTERNATIVE PIPE MOUNTING METHOD BELOW & decide 4 yourself which way you like better.

Another choice for controling secondary air flow is to stick different size (diameter) bolts into the end of the pipe to restrict air flow as appropiate. Not as eliquent as screwing on an old water valve but it still works,but you need a plier so that the hot bolts wont burn your fingers.

The reason I say old water valve is that the heat drom the stove will probably cook the seals of the water valve, but the water valve does not need to seal,it only needs to restrict some of ,say 75% of the secondary air, as a adjustment to secondary air volume into the stove.

The diameter of the black iron pipe that you use is not critical, but the smallest you could get away with is 3/8 inch internal diameter. A larger internal diameter will delever more air & make the stove heat better, so 1/2 inch internal diameter is not a bad choice.

BUT REMEMBER,it is a trade off , while the bigger pipe diameter works better, it requires a bigger hole to be drilled
to install it ,with a larger drill bit & the larger pipe thread tap & handle.

ALTERNATIVE MOUNTING METHOD FOR BLACK IRON SECONDARY AIR PIPE. This will save you the cost of a pipe tap & handle & the tapping effort. Have the pipe threaded for 2 to 4 inches at the plumbing supply house &
buy a female pipe joiner. Cut the jointer so as to make a1/4 in or 3/8 inch nut out of it.MAYBE THE PLUMBING SUPPLY HOUSE CAN SELL YOU A PIPE THREAD NUT!!! I don’t know because I never tryed to buy one.
Not you just drill the proper diameter hole through the stove wall, screw on the nut on the pipe, put a flat washer in front of the nut & place the pipe thread through the hole in the stove wall. On the outside of the stove ,place a flatwasher on the pipe thread & screw on the other pipe nut tight. You are done mounting that secondary air pipe.
You may need a support for the ends of the secondary air pipes or you may not. If you do,a pipe support strap can be used, just loop it around the pipe at its free end & put a nut & bolt through the loop & run the other end up to the top of the stove where you will have to drill a hole 7 put a 10/32 machine bolt & nut to secure the pipe strap. Make sure to use flat washers on both sides of the stove top so that smoke won’t get through the edges of the hole you drilled. If a bit of smoke does, a pat of retort cement will stop it.

Principals of secondary burn. What is required to create secondary burn is: preheated primary air, preheated secondary air and a steel baffle plate over the inside top of the stove to create a long flame path for the burning wood gases to get to the exit flue. Fire brick, if you do not already have it,is necessary on the bottom, both sides going 1 brick width or length up & on the back wall also. I used 1 brick width up,just laying the brick sideways & it worked good enough for me. I didn’t even put brick on the back wall & could not incorporate the baffle plate into the stove because of the stove’s unique design preventing it. AND I STILL GET GOOD SECONDARY BURN. You don’t need to cement or mortar the firebricks tohether ,just laying then down in there is fine & good enough, but you do need high temp firebrick as ordinary cement brick won’t last even a couple of weeks before cracking.

******************************************* There should be 3 to 4 inches of space between the inside of the top of the stove & the baffle plate.
The baffle plate creates a secondary burning chamber between the top of the stove & the baffle. The baffle may be mounted either flat or on a pitch up so that the smoke can flow up the pitch into the entrance of the secondary chamber. *******************
The baffle plate starts at the back of the stove, touching the back wall, actually sealed with retort cement where it touches & touching the side walls on both sides, sealed with retort cement. The baffle plate should come 3/4 to 7/8 of the way towards the front loading door before stopping & letting the burning smoke up into the secondary burn chamber that was created by installing the baffle plate. NOTE: You don’t need to seal the sides & back of the baffle plate but it will be more efficient if you do. Please remember the glass door warning & plan to keep the baffle termination & first secondary air pipe well away from door glass. ****************************************
A NOTE ABOUT RETORT CEMENT, also furnace cement,stove cement, any high temp cement for furnaces or stoves.
comes in a caulk gun tube or a pail of different sizes at home depot,lowes, or most hardware & plumbing & furnace,oil burner & wood stove stores.

I would not trust the black 1200 deg silicone seal inside a stove & the 450 to 600 deg not at all suitable.
retort cement runs 2000 deg to 3000 deg rating.

**************
The baffle plate can be welded in or holes can be drilled in the side of the stove & 1/4 × 20 machine bolts,nuts & washers used to bolt on a support bracket. also smaller sizes of machine bolts can be used. the conor brackets sold at hardware stores for wood screen doors & woodwn drawer reinforcement can be used as bolt on support brackets to hold the baffle plate. ******

NOTE; ALWAYS USE BOLTS THAT THREAD ALL THE WAY TO THE HEX HEAD , WITH FLAT WASHERS USED UNDER THE HEAD & INSIDE THE STOVE WITH A BOLT TO HOLD THE WASHERS TIGHT FOR A SMOKE PROOF SEAL. *****************
TOOLS YOU WILL NEED :
acetlyeene / oxigen tourch very handy, tool of choice, if you have one, but not at all necessary.

Assuming that you dont have the act/oxy tourch, I did not when i converted my stove,

YOU WILL NEED: a good 550 rpm 1/2 in chuck variable speed reversable heavy duty drill ,120 VAC & a set of high speed
metal drills suitable for drilling 1/4 in soft steel.
Extra drill bits , sold 2 in a pack from sears, for the sizes you dull out the most.

WWW.CUMMINGTOOLS.COM SELLS such a drill for $40.oo to $50.oo range, is where I boiught mine from.

TIP; WHEN DRILLING STEEL,START WITH A 1/8 “ OR THE SIZE SMALLER & MAKE PORGRESSIVLY LARGER HOLES WITH EACH NEXT LARGER DRILL BIT UNTIL YOU GET TO THE DIAMETER HOLE YOU WANT. MAKE SURE TO KEEP YOUR DRILL BIT TIP CONSTANTLY WELL LUBRICATED WITH GREASE OR OIL, AS THIS LUB IS THE LIFE OF THE DRILL BIT. No lube = dull drill bit in only 1 hole drilled.

***********************************
SO FAR,I HAVE ONLY TALKES ABOUT THE BAFFLE; NOW I TELL YOU OF THE SECONDARY AIR PIPES that you will have to install just under the baffle & as close to the baffle as you can EASILY manage. It is not critical if the secondary air pipes are 4 inch away drom the baffle instead of 1 or 2 in away, BUT YOU WONT BE ABLE TO GET
MORE WOOD INTO THE STOVE IF YOU USE UP MORE ROOM WITH A 4 INCH SECONDARY COMBUSTION SPACE
ABOVE THE BAFFLE & THE SECONDARY PIPES 4INCH BELOW THE BAFFLE.

This would rob you of 9 inch of wood you could put into your stove , resulting in a smaller fire. Not a big deal if the fire is smaller, but bigger is better. If you make the secondary chamber only 2 or 3 inch & the pipes only 2or 3 in below the baffle, you pick up space for more wood.

*********************
I did what was easiest for me to do, don’t turn the job into a nightmare by insisting on too compact of an instalation, unelse you really want to. I like fast & easy ,myself, even if I have to sacrifice a little efficiency. **************************

Next, we look at how we get preheated primary air for the stove. Some older stoves have primary air through the door & you can make a steel shield ,on standoffs, attached to the door from inside, & just in front of the primary air intake. AS THE COLD PRIMARY AIR enters the stove , it hits the hot shield, & is forced to flow along the shield ,picking up heat from the shield, until the air can exit into the main firebox of the stove from the edges of the heat retention shield that you installed. *******
The shield should be 1/4 to 3/8 in off the door & you can determine appropiate places to drill air outlet holes, as well as their diameter, in the shield if you can’t get enough primary air flow from the edges of the shield. ********************

Maybe you stove uses a different primary air intake setup. You make be able to route the primary air through some type of steel pipe or sheet metal duct for a short distance , so as to preheat the air, before releasing it into the firebox. KEEP IN MIND THAT PREHEATED PRIMARY AIR IS very IMPORTANT , but not critical, to secondary burn. you stove will be much more efficient if you can make some kind of a stab towards at least a little primary air preheating, as it could raise your stoves efficiency by 10% to 15 %.

THE HOTTER YOU CAN KEEP THE INSIDE OF YOUR STOVE, THE EASIER TO INITIATE SECONDARY BURN.

SECONDARY BURN USUALLY NEEDS 500 TO 600 DEG stack temp to initiate, but once secondary burn gets going,
while stove top temps could stay at 500 to 650 deg, stack temps will drop down to 400 deg.

Wet wood , high moisture content wood & unseasoned wood, only give a 350 deg to 450 deg fire until the moisture can be cooked out of the logs; which usually means until the logs are charred 1/2 inch to 3/4 in into the wood; so don’t expect to get a secondary burn from this wood , as the fire is too cold to initiate secondary burn.

So , what can’t i remember that i need to tell you , preheated primary air, preheated secondary air, a means to control both primary & secondary air flows, a baffle plate to create a long flame path & a secondary smoke burn
chamber above the baffle plate & below the stove top with the smoke burn chamber going to the top mounted stove pipe in back, or the rear mounted stove pipe in back with appropiate baffling so that the smoke must pass only thru the secondary burn chamber in order to get to the stove pipe & firebrick to make the stove hotter.

WHY BOTHER TO DO ALL THIS? HERE IS ONE GOOD REASON.

Old time stoves ,like the all nighter papa bear, had 1/4 in steel plate & 12 cubic foot fireboxes & were capable of putting out 120,000 btu to 200,000 btu per hr. New stoves can’t match this btu/hr output unless you go to a wood fired hot air furnace.

Another reason is that it is a major PITA to get that 800 lb stove out of the basement, so why not make it fuel efficient instead.

I JUST REMEMBERED!!!!! SECONDARY STOVES ARE NOT AIR TIGHT & should never be snarffled down to a smoking simmer that stinks out the neighborhood for a all night burn.

When you shut off the primary air on a modern secondary burn stove , the primary air contol is factory preset so that it does not shut off all the air , but instead only shuts off 80 % of the air. This is to prevent the owner from smoking out the neighborhood by shutting down the air so that the fire smolders all night long. It is designed to keep some flame on the wood to prevent smoking of the chimney.Also, the secondary air tubes provide more air to the firebox.

POINT IS, DO NOT EXPECT YOUR STOVE TO SMOLDER DOWN FOR ALL NITE BURNS, like it used to.
You can expext a 4 to 5 hour burn ,if your firebox is big enough to hold enough wood & then that the embers will remain hot for another 4 to 6 hrs, so you should get 8 to 11 hr of heat, but only 4 to 5 hr of flame on the wood.

Some air will always be passing through your stove, although with your old time controls , you probably can still snarffle down your stove to smolder all night, especially if you block off secondary air, but really, why bother.
The neighbors will hate you for smoking up the air unelse you don’t have any neighbors within 1/2 mile.
How very nice,wish i lived there. Here ,i am surrounded with people looking for the least oppretunity to do me for whatever they can manage.

Anyway—-best of luck with your project.
If you have questions,PM eernest4 on hearth.com