Secondary air modification complete, here's hoping I smoke less!

[HaTaX]

I've got a 1984 NightWatch made by Minnesota Stove Works (Company is defunct now, was around over 120 years prior to '84), and it's an old smoke dragon style insert. The only saving grace it had was a smoke shelf over the flue where some nice secondary burn would occur occasionally. I think where the primary air came in, it traveled along the channels for the firebrick to the back and that's why I would see it now and then back there prior to the mod.

I started this about 2 weeks ago where I setup a ladder style air supply and originally had the secondary air coming through the primary draft opening. This was just to see how it did as a proof of concept, and it worked quite well except I didn't have good control over the burn overall. Starting from cold was a bit of a fight, and once it was going it was difficult to throttle back. Basically you had to somewhat babysit it and I'm going to assume it was because of how much the primary draft was affected by my modification. If you'd like to see some pictures of how the secondary air worked in my proof of concept setup, there are some pictures in this thread: https://www.hearth.com/talk/threads...ve-slammer-install-looking-for-advice.103780/

To finalize it, I drilled a 7/8" hole just above and to the side of the primary controls, and used 2 x 7/8" SAE washers to get the required thickness between the pipe fittings. The outside washer and elbow are sealed with furnace cement, and from there it goes into a 45 degree street elbow in the firebox.

During this process I realized the left and right side are not symmetrical and it makes sense to me now, many of these units were shipped with non-glass front doors and the air controls were on the doors in that case. You can see where one firebrick is removed from each side, and they just knocked a hole in there and welded a section of flat steel to hold the draft and air plate on. Heck, the air plates themselves are even very different from right to left side, makes me wonder if it was just spare parts to put it together or if they were going for a swirl effect or something.

Anyway, the rest of the pipe is 1/2" black pipe and the air holes are 3/32" and 5/32" depending on where they're at. I figure if I've got too many, I can just fill them with a little weld in there but I doubt I've got too few. Spacing of holes are 1" on center, and each section of ladder is 18.5" long, so there's about 54 holes total. I also drilled a few on the back side of the pipe that is facing upwards on the back 2 pipes, these are aimed at the existing smoke shelf to provide some direct air in that area.

Once the cement sets up I'll fire this beast up tomorrow and see how it does! I'm kind of anxious to see how it performs with a proper air flow and I'm hoping I'll be able to regulate the burn a little better now.

The second week of February I'll be installing a full chimney liner for this as well, currently it's a slammer install and I know that needs to be resolved ASAP. Hoping that I'll be able to get a little more heat from it after that is completed. Eventually this thing will be replaced with a Blaze King Princess Insert, most likely before the next winter season. We'll see how it does with it's new pipes before making a decision.

 

[pen]

You are lucky to have glass to be able to view the results! I'm looking forward to seeing some flamage in there.

Also, there's a good chance you created a whole new stove there. Look for new parts of the stove to be your hottest areas.

pen

 

[HaTaX]

Hopefully I'll get some decent pictures tonight or tomorrow from it! There's a few pictures of the rough draft version producing some nice secondaries in the linked thread, not sure how much those will change overall with putting the primary air controls back to the way they were originally.

Right now there's candles inside the firebox with the flame just below the pipe where it enters, just trying to give it a little heat to help it with the curing process. Then I'll do one little fire before going nuts with it, just trying to make sure I cure the cement properly.

When I had it running with the rough draft version I noticed my stove top temps were higher throughout the middle of the burn, about 550-600. I used my IR on different areas, but the hottest area seemed to be middle of the top, about 6" back from the front of the stove. Normally the hottest area is a little further back closer to the outlet, I'm guessing the baffle and brick I added are bringing that heat a bit more forward on the top plate. If anyone is curious, firebox dimensions are 22" deep x 22.5" wide x 14" tall so I'd say I've got about a 3.2 cf firebox taking into account the smoke shelf displaces some of the available space and the fact that I normally don't use the front 4" of space to keep glass clean and it's then beyond the firebrick.

The stove is built like a tank, top and bottom plates are 5/16" and the side is one big solid piece of 1/4" steel, bottom is completely covered in firebrick and about 3/4 of the way up the sides is lined with firebrick. I've had stove top temps up to 700-750 before with no ill effects, at least nothing I could see warped or deformed, I'm assuming this thing can take a little bit of a beating. (Unlike some of the newer cast stoves I looked at, cast for some reason scares me above 600) And hell, if I kill it, it's just an excuse to get the Blaze King Princess a little earlier.

 

[ScotO]

I hope that pipe holds up for you. Black iron will take a beating in that kind of heat. Most secondary tubes are made from stainless steel for this reason. But I am anxious for your experiment to commence! If this works out and the pipes don't last, you can build the same setup out of stainless steel and get many years out of it. Keep us posted.....

 

[Motor7]

Most don't have the nads to cut and retrofit their stoves....

 

[HaTaX]

Heh, thank you sir for the nod to my nads, the boys need a little affirmation from time to time. :D

Just put a new door gasket on it, wow was the old one bad. I noticed it today while I was checking the candles and letting the fixtures cool a little between heat on them, there was cold air just pouring out around the doors and I knew that was going to make draft control difficult at best... Grabbed a gasket kit and a few other things from Menards and I latched the front doors a little over an hour ago so it should be good for a small fire here shortly. While I was at it I added a section of gasket between the two doors where there was none previously, while dry fitting it a dollar bill still wouldn't pass near the center so I figured it was safe to add, that closed up the last of the cold air the doors were leaking.

On another note while I was at Menards I grabbed 2 packs of these to try out: http://www.menards.com/main/heating-cooling/fuel/wood-fuel-blocks/p-1712204-c-6855.htm They're $5 for a package that weighs 38 lbs, not sure how they'll do yet but they looked to be cheap and decent as they use no glue and are safe for airtight stove use. They look a little easier to light off and might be nice to toss in at the front of a large split load, no clue yet. I'm sure I'll figure out something they're good for, and if not, off to the neighbors for their open fireplaces...

 

[HaTaX]

I hope that pipe holds up for you. Black iron will take a beating in that kind of heat. Most secondary tubes are made from stainless steel for this reason. But I am anxious for your experiment to commence! If this works out and the pipes don't last, you can build the same setup out of stainless steel and get many years out of it. Keep us posted.....

I'm a little apprehensive on the lifespan of the black pipe as well, but some others have had theirs in a furnace over 2 seasons with no serious degradation, so these pipes might just outlive the stove. If things do work out though, I am completely with you on the SS solution. Ideally I'd use factory looking draft spin knobs on the outside with the SS inside sealed to the opening, that eliminates the gate valves, looks better, and should give me back a little more space inside the firebox since I'd be fabricating it all from scratch. Hmmm, I'd have to bug my neighbor for his TIG welder...

 

[HaTaX]

Well I started a fire up last night around midnight and fell asleep next to it for a bit. Getting it going was a royal PITA as temps have gone up here and we recently got some rain / ice / snow and I had to work that humidity out of the chimney before I had a nice draft. (Will be so nice when I get my liner in)

After drying the flue out for about an hour it was drafting nicely and I was able to get it into a groove. I used just one mid sized split and a few of the gren heat bricks. Trying to keep the top temps from getting too high as I wanted it to get to about 350 degrees top temp and then let it cool before the AM to help cure the cement and gasket seal.

When I woke up I took a few pictures and a video and went to bed. I was really surprised though at the overall performance of it though! Normally I can't damp the primary air more then at least 2 revolutions of the spinners, but I left it at about 1/2 of a turn open on the primary and opened the secondary air all the way up and it was happy as could be there. I was producing nice secondaries with a small amount of flames on the bricks / log, and it was sustaining itself. I think I actually captured two pictures that have the "ghost" flames present. (Almost see through / very faint glow that look like a sheet of fire)

Big change from how it used to behave, there was really no low to mid throttle on this thing, it was HOT or it had no fire in it. Some of this could be from the leaky gasket before, no real way to limit the air intake when it was leaking that bad, but I do know that a nice 350-400 degree top temp for the evening was perfect when it's not very cold outside.

Also as a bonus, today about 6 hours later I found about 5 coals that were still hot, and zero blackened coal chunks. Probably the gren heat bricks at work there, but normally I find 10 or so pieces of black coal that didn't get burned in the morning, this time it was all just white ash.

I'll try attaching this video in here as a link, I'd rather not go through the trouble of putting it on youtube. It's just a short 20 second video of the flames in action. Let me know if the link does / doesn't work for you all: http://forward-thinking.net/SecondaryFlameVid.mov

 

[HaTaX]

Well, now I'm gonna get cooked out of my house... I am currently running pretty hot (500-600 top temp) to finish the cure and see how it does with a little more wood in there. With just 5 medium sized splits I have no problem reaching 600 top temp, seems better then before!

I'm able to almost fully close the primary air draft, I can go as far down as 1/2 turn open from a complete close on both sides and the secondaries will sustain themselves no problem. Any lower then that and I think I'd start losing too much heat from the coals, maybe I could get it to 1/4 turn on both sides with some tinkering and timing.

Smoke difference is amazing, I threw some wood & bricks in there and headed outside to take the ice off the driveway before it gets very cold this eve. While I was out there it was doing it's smoke dragon thing and it looked like a small house fire on my block. :D After I went in, I opened up the secondaries and started reducing the primary air. I took a picture of my chimney about 10 minutes later when the top temp was 450, it's attached below.

Other pictures are just gratuitous shots of the secondaries as best as I could capture them (I need to play with my camera settings). I grabbed a few videos as well, but it was really a trip to see almost zero flames on the bottom, yet there's a very alive fireball rolling around in the top of the stove. I even saw quite a bit of combustion occurring above my pipes between the baffle I made and the top of the stove on the way to the outlet, that surprised me and I know I'm getting good heat from that fire up there. You can kind of see it in the HotSecondary2 picture, it was hard to get in a picture but I've got some videos that show it clearly.

 

[Motor7]

Hatax it looks like you did very well. I think Schedule 80 pipe will hold up pretty good, if not it's way cheaper then SS pipe. My Hearthstone only has one secondary. Looking at it I think I can add another one without cutting any new holes. Also my shop stove, an old Buck copy really needs secondary's, so this summer I am going to do some mods to it and add a waste oil drip. Good job and keep us posted on the longevity..........

 

[HaTaX]

Thanks for the kind words! Just packed the box full with 3 large splits and a few mediums on top to pack it full, placed on a nice sized bed of coals that was just coming down. Let it run with the primaries opened 2 turns and once the top temp got past 400 I tightened it down to almost 1/4 turn. Spiked to 450 and has now settled in at 425 top temp with the secondaries roaring, still getting some decent log flames, but the majority of the flame volume is at the top. It's kinda weird, at first 2-4 secondary holes come to life with small flames around them, then within 15 minutes there's 15-20 of them going. I'm going to time this burn and see what I can get from it, I'm expecting at least 8 hours I'll still have decent coals.

If nothing else, it's a neat show while they're active.

 

[HaTaX]

Geez, guess I can damp it down further if I can keep the fire from going out. With just some dancing flames in there the top temp is 600 now, doesn't look to be nearly enough flame for that, but the IR agrees. If I lean down and look at the top I can see flames burning on the front section of the box where the air from the secondaries spills upwards, guess there's a fresh supply of air for the smoke that's in that area now!

It's only 30 outside, 600 degree top is going to have my wife asking why it's 80 degrees in the house when she wakes up... Hehehe

 

[begreen]

Looks like a good improvement. Nice job. You will have fun getting used to the new config and tuning it in. It's pretty common to leave the secondary air open and reduce the primary until the flames get minimal and lazy. As long as there's no smoke coming from the chimney, it's burning well.

So what's next? Rerouting the side air up and over the glass for an airwash?

 

[HaTaX]

Well, I got a 10-11 hour burn out of it last night and now there are about 2 or 3 slightly smaller then fist sized coals in there still glowing along and top temps are just under 200. Little colder then I'd like, but still pretty good stuff! Not sure of the smoke levels out of the chimney last night, I couldn't see much of anything when I put the chimney between me and the moon and normally I'd see some haze whisping around so I think that's a good sign.

Next steps? Heh I actually started thinking last night "Hmmm, pretty sure there's enough room up there for a cat still, how much headache would that cause me?" But then I stopped myself, installing a cat would be fun, but a bit more $$ then I think I want to invest in it. (And time, that wouldn't be a 2 hour project) There's actually an airwash system in there that keeps the lower 3/4 of the glass pretty clean, the primary drafts have a plate to divert air to the glass. During the early testing I found out that they are actually functional as my glass was pretty nasty after just one or two loads in there, I had the plates removed so I could run the black pipe in through the primary air drafts. One thing I am looking into though is improving the baffle area, maybe go with a full length plate in there or some other trickery to button up that area. As it is, if the box is full of smoke and you open the doors too quick, you'll get some smoke rollout which never used to happen. Pretty sure that's because the smoke plate is now extended about another 6" from where it used to stop, not an issue really more so a learning curve thing.

I'm sure I'll figure this "new" beast out over the next week or two, and I bet the liner will change the behavior yet again.

 

[TX-L]

I love old stove mods. I recently bought the baffle, secondary tube, and bypass components for a Lopi Liberty, am going to put them in an old Lopi 520 sometime this winter. I'll try to take pictures before, during, and after the project; and share them on here.

 

[valley ranch]

Looks pretty good, are you happy with the size of the air entry? Looks like 3/4".

 

[HaTaX]

I've been away for a bit, had an ice fishing trip up at lake of the woods this last weekend and have been playing catch up.

Before I left I ordered up 2 ACS Powders and a 1 gallon of the ACS spray to help with my creosote glaze, TSP and a wire brush were gonna take a while to clean that mess. So I crawled up on the roof friday evening and coated the flue nicely with the powder. Probably did more then 4-6 squirts, and I may need a second application depending on how this goes. There's some wet snow forecasted here the next few days so I thought it would be best to run the hot burns through it tonight and while it snows. The ACS had about 48 hours to sit with no heat, and tonight it will get a nice hot burn while I douse every load that goes in with the ACS spray. Hopefully this will break the glaze down enough I can remove it myself.

All this to prepare for the liner that I ordered on friday from Dynamitebuys (great people there BTW), I went with the DuraLiner rigid product with a flex connector through the damper. It will be so nice to get rid of the slammer install, I'm looking forward to chimney cleanings taking far less time as well.

The inlet pipes are 1/2" on each side, which seems adequate but 3/4" might have netted me a little better secondary performance. You really do want the air to travel through the pipes as slowly as possible to gather as much heat as possible before exiting one of the holes. When it's going full rip, I can almost shut down the primaries, ideally you should be able to shut them down completely, so I guess that says I'm just a little short on pipe size. If you've got the space, screw it and go with 1"

Still very happy with it! When I just started the fire top down, the primaries were active within 15 minutes or so, didn't take long at all for them to get up to temp with the fire next to them. If anyone has a little spare time and has one of these old smoke dragons in service, I think it's a great mod to breath some extra life into them.

 

[Ehouse]

I just got a Hearthstone Harvest for next to nothing. picking it up this week. The cat is gone, so rather than replace it, I'd like to try adding some tubes. This thread and the one on the Hearthstone 1 give me hope.

Ehouse

 

[valley ranch]

Ha Tax, You did a nice job. Been wanting to do this to my Centennial for years, maybe I'll get to it this year. I think about it each time I build a fire. Have a good day.

 

[HaTaX]

Thanks guys, glad it gave a little inspiration to try it out yourselves! I really thought I'd have to babysit it a lot more often, but I've found if I want less heat I just pack the box with less wood and have shorter times between reloads. Easier to regulate the heat output that way then messing with the gate valves and primaries constantly.

So this way my primary air adjustments are always between 1/2 turn to 2 turns open, and secondaries are fully open unless top temps are under 250-300. Anything below those temps and having secondaries open seems to just prolong the warmup. One exception to the rule, when I'm starting from cold, I build up larger logs on bottom to small splits and starting pellets at the top. I start the fire top down with some cardboard and it seems to really heat the secondary area up quickly, in this case I just open them up from the start and it's over 350 or so in about 15-20 minutes. Then I damp down primaries and they pretty much sit wherever I've set them till I let it get to a low coal state.

After running it the last few days and trying to not spend much time messing with it, I'm very happy with how it runs after the modification. I was outside shoveling yesterday after I had just thrown some fresh logs on the fire. When I was outside I first smelled that smoky wood smell and saw some smoke out of the chimney. Within 20 minutes the smoke was nearly gone completely and I could still smell the faint whiff of wood burning. Made me very happy I didn't have to mess with it, just load and go, I was probably just being anal retentive before wanting to watch / tweak it. If it keeps up running like this I'll be hard pressed to come up with a reason to replace it...

On another note, looks like the ACS powder is doing it's thing as the top half of the flue has gone from a shiny black surface to a velvety brown. Since the fire was very very low I decided to dump a little more powder down there and I'll torch it up again this evening. Hopefully after a week or two of this regimen I'll be able to brush out the glaze and get it all cleaned up nicely before my liner shows up.

 

[Corey]

Looks like you're getting it dialed in. One thing to play around with is the balance of primary to secondary air. Too much primary air wafts the flames through the firebox so fast, they don't have time to transfer heat...too little and you get a smoky cold fire which may not put enough heat into the secondaries. Once the secondaries do light off, too little secondary air can allow unburned gasses/smoke up the flue, too much air in the secondaries cools the burn tubes off. But once you hit it and get 'dialed in' it's amazing how little flame/fire is needed to keep the burn clean and the stove top at or over 600ºF.

I love peeping inside the stove to find the secondaries and top baffle glowing orange hot while just the wisps of translucent blue-purple flame waft around up there and the stack just has some heat ripples rising out with no visible smoke at all.

 

[new england tommy]

Most don't have the nads to cut and retrofit their stoves....

We should do this!

 

[HaTaX]

Sure is fun to watch the secondaries in action, I didn't expect to get much using these Gren-Heat bricks but they really do go through a long gassing out period when the stove is hot enough. Lately I've been mixing one or two wood splits in to get the fire going with these, but once it's to life I can feed it bricks all day long with no problems. Tonight the top temp was 250 and I moved the coals around and put 5 more on top of the coals. 10 minutes later I brought the air down to 1/2 turn open and the whole top of the box is engulfed in flames.

I always thought all the 'bricks' were bad news in wood stoves but these things really work well and are cheap. I'm going to try to stick to them as much as possible until the end of this burning season, they should keep creosote build up to a minimum and I won't need to even think about humidity content.

 

[HaTaX]

Well, I'm still learning apparently! Threw 4 of the gren-heat bricks on a medium sized bed of coals, stove top was ~200F, I let it get going with the primaries wide open for about 20 minutes. At this point the secondaries had been going for a few minutes and were covering the baffles pretty well so I decided to go all the way down to 1/4 open on the primaries and left the secondaries wide open.

Result? Secondaries are still active almost 5 hours later but have been quite small after the primary air was reduced. I figured they would go out honestly, and every time I've gone to check on it they're still dancing around in a 10" area but have been moving around from left, center, and right. Stove top is deceiving at ~300F as the blower is on low and the house is staying at 71 degrees upstairs (outside temp is 35F). So looking at the thermometer would tell me that it's not burning hot enough, but without the fire raging I don't get as much heat up at the top plate. Outside all I can see is heat distortion from the chimney, not even a faint wisp of smoke.

So when burning very low I have to keep an eye on the flame much more so then the thermometer, looks like the added baffles and bricks are keeping that heat where it needs to be!

Watch, I'll put the liner on and have to re-learn this thing all over again...

 

[pen]

Is the air from that blower going over the thermometer and lowering it's reading?