# Silent Flame Retrofit - Secondary Air, Firebrick, etc..



## Mr4btTahoe (Oct 19, 2015)

Hey guys...

Ive really been tossing around the idea of baffling my old stove and adding a secondary burn system..   but the question is will a secondary burner function on a stove that isn't air tight?

Where the doors on my stove close, there is approximately a 1/4" gap between the doors that is covered by an overlapping plate on the right side door...   however at the top and bottom, the gap is open.  The air flow through the gap is minimal at best as its not enough to maintain a slow burn if I shut the main air down.

Thoughts?


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## mellow (Oct 19, 2015)

https://www.hearth.com/talk/forums/classic-wood-stove-forums-prior-to-approx-1993.19/

Plenty of talk about conversions in the Classic section, do a search for secondary in there to bring up a whole bunch of results.

Hrmm.. search is acting wonky at the moment,  here is one I had bookmarked to get you started:  https://www.hearth.com/talk/threads...-for-secondary-burn-now-have-questions.60181/


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## Mr4btTahoe (Oct 19, 2015)

Thanks bud.  I tried a search earlier and it kept coming back with errors.


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## begreen (Oct 19, 2015)

The forum software is getting updated and search is one of the victims of the update. It will return soon I hope. In the meantime I've moved this post to the Classics Forum.

Some stoves are better for a baffle and secondary tube retrofit than others. What stove make/model is this? Post a picture if that helps.


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## Mr4btTahoe (Oct 19, 2015)

The stove is a Long Mfg. Silent Flame  Model # 1653. 

They have been out of production for quite some time from the research I did in the past during the install.  There are a few pics of the stove on my install thread from last winter...
https://www.hearth.com/talk/threads/first-time-install-a-few-questions.139253/

I'm sure I can get the needed heat by adding an upper baffle to the firebox (ive got plenty of vertical space in the box)...   my my fear is the air leak at the door gap..  if it will keep the secondary system from functioning.

The stoves I've seen retrofitted seem to have solid doors that are "air tight" designs.


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## coaly (Oct 19, 2015)

It takes an air tight stove. Here's why;
Heat rising up the stack makes a low pressure area in the flue, (lowest at the stove collar) and inside the stove. Any air leak will allow atmospheric air pressure to leak into stove - raising the pressure, meaning no vacuum or void. The vacuum is what allows the higher air pressure outside the stove to rush into the primary intake. A stove with secondaries has a second intake that leads to the tubes above fire. When the primary intake is closed, oxygen is pushed into the only place it can get in. The secondary inlet, through the little holes in the intake tube where the smoke is. Any leak into stove allows atmospheric pressure to take the path of least resistance and not enter through the secondary inlet. This is why chimney height and diameter is so important as well. It has to create enough pressure differential for atmospheric pressure to be high enough outside the stove, compared to inside. You can see how any leak would balance the negative pressure you're trying to create with the chimney..


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## Mr4btTahoe (Oct 19, 2015)

Thanks for the input...    I had a feeling it wouldn't work without sealing things up a bit.

Other then the door gap...   its sealed up fairly well.  I believe I'll toy with it a bit and see if I can get it sealed up enough to function.  I added door gaskets to it last year as it didn't have any to begin with.  I'm sure I can find something to seal the gap between the doors.

I decided to move forward with my tinkering and half arsely built an adjustable baffle (smoke rack).  I cut a piece of 1/8" plate to fit the stove and tacked a 1/2" nut to each corner.  I then cut some 1/2" rod and threaded the ends to make adjustable legs.  I've read that just the addition of a baffle can greatly increase the efficiency of the stove...  so we'll start here.  (Yes the rods are pink..   its all the bar stock I had laying around...   and they wont be pink for long.  lol)













If the baffle works well during the test fire tonight, I'm going to pull the baffle back out and stiffen the 1/8" plate up a bit as I'm sure the high temps will warp in in short order if I leave it as is.  The area of the gap at the front of the stove is just a few sq. inches larger then the area of the flue.  I currently have the baffle sitting flat but can adjust its angle a good bit and toy around with it to see what makes the biggest difference.  With the baffle in place, I am still left with just over a 4 cu. ft. fire box..   didn't loose much usable space as the factory damper, when open, takes up 4" or so of vertical space.  The baffle was set to clear the damper by 1/4" or so.

I wont be able to do any real testing until I pickup an IR thermometer (hopefully this week) but I would think I'll notice a difference in output or wood consumption either way.

We'll see.


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## coaly (Oct 19, 2015)

Is the flue size the same as stove outlet all the way up? Insulated flue or liner?
I ask because getting more heat out of the stove is great with the correct chimney. If you require more heat in a less than optimal chimney, the baffle is going to add to creosote problems.
The first thing I noticed was less smoke.
If you get smoke roll in opening doors, try lowering the back first. Angling the plate upwards in the front increases flow speed out and decreases flame impingement. Impingement is a negative effect cooling the burn zone by absorbing heat from flame tips touching plate. But is compensated overall by a higher fire box temperature. You will also get areas of stagnet air movement in the corners with a baffle that doesn't have the corners clipped.
The thinner the plate, the hotter it will be which takes less heat from the flame tips which keeps the burn zone temp higher. Of course warpage becomes the problem. 1/4 inch plate does good up to about 18 or 19 inches wide. Over that, 5/16 stays flat.
Is there firebrick in the stove? That increases firebox temperature reducing emissions as well. If not, the baffle plate with angle iron around the edge facing down is good for holding them in place. Pictured below;


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## Mr4btTahoe (Oct 19, 2015)

The stove is free standing with 8" double wall up to the ceiling and then 8" double wall class a.  The stack is vertical with no bends and is above the peak of the roof several feet.  The stove drafts extremely well and is typically very easy to light even in warmer weather (50+)

No firebrick in the stove.  I've strongly considered it but was worried about cutting down on useable firebox as I want to maintain the 12+hr burn times...

I will definitely have to reinforce the plate as it spans 22.5" wide and 13.5" depth.  I will add some support to the plate or upsize the plate once I know it works well.

First impressions are good...        I started a small fire which seemed a bit harder to light then normal.  The burn rate was much slower even with the door cracked open...   however once going, the heat output seems much higher for the minimal amount of wood in the box.  The t-stat kicked the blower on much sooner then it normally does...   and the flames in the box have a blue/white hue to them now instead of orange/yellow.  Smoke output seems to be down a good bit as well but its hard to tell as the moon isn't out and I'm out in BFE with no outdoor lighting.

It may just be in my head, but it seems to be taking quite a while to consume what I've put in the box.

Once its cooled down (tomorrow after work), I'll pull the baffle and weld in some 1/2" bar stock to stiffen the plate up a good bit (or replace the plate) along with trimming the corners a bit (or perhaps drilling the corners would work?) to allow for better airflow in the rear of the stove.  I could also move the baffle out say 1/4" from the rear of the stove...

Thanks for all the input!
-Chris

-EDIT-
Jus went out with the spot light...    smoke is completely gone!  Last night burning the same wood/load, it was smoking heavily.  Looks to me like the baffle may have done some good.


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## Mr4btTahoe (Oct 20, 2015)

Perhaps a problem with the baffle....

Before installing the baffle, I could load the stove with a hot coal bed and it would take off  and burn well...       However with the baffle in place and a hot coal bed, I'm finding it hard to get my normal large pieces to stay rolling...   I almost have to keep the door cracked open to get enough air movement to keep things rolling (even with the air controls at wide open.

With smaller pieces, it doesn't seem to have a problem...

Thoughts?

I'm certainly going to have to alter the baffle...  but I do want to keep it as I like the clean burn I was getting.

Perhaps I need to split these blocks to smaller sizes?

Plan for tomorrow after work is to shorten up the rear legs a good bit and possibly shorten the depth of the baffle an inch or 2.  Right now, the opening between the baffle and the front of the stove is a little more then 2"..       plenty of overall area but it doesn't seem to flow enough.


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## coaly (Oct 20, 2015)

You're masking the problem with smaller pieces. They get more air through them. Lack of air in stove is from lack of draft.

For the efficient baffle you're trying you need a 6 inch flue. The area of the 8 inch is only capable of more flow, it doesn't create more flow. (reducing to 6 is about HALF the area to heat inside chimney). Without baffle, much more heat was lost and was keeping the flue above the critical 250* temp all the way to the top. An IR thermometer will tell the story. The baffle will keep so much heat in the stove, the draft will slow and form much more creosote. Making the stove more efficient means more heat inside and less out. Your current chimney requires much more heat, so tilt baffle plate first, then adjust by opening the smoke space above baffle. It should be low in the back, and long enough to cover the exhaust outlet when looking straight down it. The smoke space, or area the exhaust travels through can be as small as the stove outlet square area, but that is with the most efficient chimney. The more heat the chimney requires, the larger the smoke space.
If you have a flue damper, it should be wide open with that size flue.
Here are two threads on baffle fabrication with posted results; The second has a video when adjusted properly.

https://www.hearth.com/talk/threads...d-fisher-more-heat-less-smoke-under-25.74710/
https://www.hearth.com/talk/threads/cant-seem-to-figure-out.119184/


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## Mr4btTahoe (Oct 20, 2015)

That makes sense.  The stove typically drafts extremely well even when cold (just lit).

The damper is built into the stove top.  Typically, once up to temp, I can close the damper down 1/2 or so and it cruises along nicely keeping the stove top and stack hot...  and as long as the wood was dry, very little visible smoke if any.

I'd say you hit the nail on the head as I could keep my hands on the stack last night..    even though its double wall, it should be much hotter.

So its basically going to be a balancing act between baffle size and keeping the stack at temp.  I'd venture to say even a small baffle will somewhat help efficiency.

I'll read through those threads and do as you say...   I'll trim down the rear legs and angle it a bit and open up the smoke space.  I could cut as much as 4-5" off of the depth of the plate and still cover the flue outlet.

Thanks for the input!


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## Mr4btTahoe (Oct 20, 2015)

I think I forgot to mention...    I'm not trying to get more heat out of the stove as heat output is great.  Just working towards cleaner burns and less wood consumption.


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## Mr4btTahoe (Oct 20, 2015)

I just thought about what I was doing last night...    After installing the baffle and getting it going, I was closing the damper as I normally would.  I'm curious if this was the cause of the issue.....    I wouldn't close it all the way but the typical 1/3--1/2 that I used to do without the baffle in place.

From what I'm reading, the baffle all but eliminates the need for a damper all together.


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## Mr4btTahoe (Oct 20, 2015)

Well...  I've toyed around with it most of the evening...   Still the same problem.  I angled the baffle and shortened its depth a good bit.  I also cut the rear corners at a 45.

With small dry pieces in the box, it gets hot quick and burns nice.  As soon as anything large goes in, it falls on its face no matter how hot the coal bed is or how hot the stack is prior.

I may try to split my blocks before I lose my coal bed and see if it makes a difference...   Otherwise, its going back to stock.


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## begreen (Oct 20, 2015)

When you re-split the wood check it for moisture. If you don't have a moisture meter press it up against your cheek. If it feels cool and damp, it is.


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## Mr4btTahoe (Oct 20, 2015)

Seemed the same temp as it was outside and dry.

This is the same wood that prior to the baffle, could be stacked tight on a hot coal bed and take off fine (got nearly 14hrs out of a stacked box just 5 days prior on the same wood).  It's odd...  Prior to the baffle, this stove would eat just about anything...  As long as it was up to temp prior to loading it down, it didn't matter what it was (it ate a 60# round last winter just to see if it would do it).

So far, it seems to like the single split pieces a bit more...   I'll know more in a couple of hours.


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## Mr4btTahoe (Oct 20, 2015)

Well...   after 2 hours, its still burning with a nice slow blue flame.

I split 2 large pieces 1 direction so I ended up with 4 small/med sized pieces.  I threw them in and let it go wide open for ~10 minutes.  Left the damper full open but closed the air down to half throttle and let it go.  Considering how slow its burning at the moment, heat output is impressive.  The stack and stove top are staying much hotter (cant keep my hand on the double wall stack).

I'd say there is still about 1.5pcs worth left in the box.  I think I'll let it go for the night and split a bit more tomorrow..   stack it full and see if I can still get my 12-14hr burn times as I could with the large unsplit chunks and no baffle.

I'm interested in why the flame color has changed...      any insight?  The flames are dancing 6-8" and are almost pure blue with a coupe flicks of orange/yellow...

Anyways...   ordering an IR gun and a moisture meter Friday.
-Chris


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## begreen (Oct 20, 2015)

You may want to pick up a probe thermometer for the stove pipe. If the internal flue gases are >350F then they are likely hot enough to avoid creosote condensation unless there is a very tall chimney that the stove attaches to.


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## Mr4btTahoe (Oct 20, 2015)

Sounds like a plan.  I'll add that to my shopping list.

Prior to the baffle, the stack would get HOT.  Its certainly running cooler now so it would be nice to see exactly what its doing.


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## Grisu (Oct 20, 2015)

Mr4btTahoe said:


> The flames are dancing 6-8" and are almost pure blue with a coupe flicks of orange/yellow...



Blue is great. It means you have a complete combustion. The more yellowish your flame is the more unburnt carbon remains as smoke. 
Congrats, it looks like you are on the right path.


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## Mr4btTahoe (Oct 21, 2015)

Well...  automatic blower kicked off at 3:45 this morning still burning down those 4 small pieces.  I'm really considering moving forward with the secondary tubes.

I'm going to load it up tonight and see how it does and if all goes well, I plan to rebuild the baffle out of heavier material.  I may also add firebrick to the stove as it currently has none.


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## Mr4btTahoe (Oct 21, 2015)

Started splitting tonight and found a lot of wet wood.  This'll be a fun winter..    lol.  Ive hauled in just over 12 cord as this is our first year attempting to heat with just wood but the majority is rather wet.

I split all the chunks down to much smaller size and stacked them loose in an area on my deck that sees a lot of sun and a lot of air...   hoping a couple months will help.   Anyway to speed up drying time?


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## zig (Oct 22, 2015)

Mr4btTahoe said:


> Started splitting tonight and found a lot of wet wood.  This'll be a fun winter..    lol.  Ive hauled in just over 12 cord as this is our first year attempting to heat with just wood but the majority is rather wet.
> 
> I split all the chunks down to much smaller size and stacked them loose in an area on my deck that sees a lot of sun and a lot of air...   hoping a couple months will help.   Anyway to speed up drying time?


Sun, wind and time  for the coming years. For now you could mix in 2x4 or other kiln dried woods with the damp stuff to help but the first year's a groan some times. You said 12 cord, and if it's ash split smaller and you can get sun/ wind to it it may dry faster. The top half of standing dead ash should be quite dry but the bottom will need a year.Forecast is for a warmer, drier winter though. Good luck.


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## Mr4btTahoe (Oct 22, 2015)

zig said:


> Sun, wind and time  for the coming years. For now you could mix in 2x4 or other kiln dried woods with the damp stuff to help but the first year's a groan some times. You said 12 cord, and if it's ash split smaller and you can get sun/ wind to it it may dry faster. The top half of standing dead ash should be quite dry but the bottom will need a year.Forecast is for a warmer, drier winter though. Good luck.



Thanks bud.  I've got some dead already dropped on the back side of the property I'll look into.  I'm hoping to get by with 3-4 cord this winter so I'll have 8 cord stacked to season next year.


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## Mr4btTahoe (Oct 26, 2015)

Well...  I ordered a Condar probe style flue thermometer, a wood moisture meter, and an IR temp gun which will all be here this week.

So back to the modifications..        I loaded some of the split wood and so far the stove seems to like it a lot more so I'm feeling a lot better about the baffle.  Heat output is high...   possibly higher then before but smoke output is almost 0 when the stove is up to temp.

Now, I was walking around my local TSC yesterday and they had firebrick for $1.99 each.  I believe I'm going to measure the firebox tomorrow morning and pick up enough to line the bottom and the sides up to the bottom of the baffle.

With the baffle..    the firebox retains a lot more heat then it did originally.  Is there risk of damage to the box itself due to the added heat retention?  Will firebrick help/hurt this?

Also..  My wood stove has an air chamber between the firebox and the outer casing of the stove..  along with a blower built into the bottom.  Will adding firebrick reduce the heat output from the blower?





Thanks guys.


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## Mr4btTahoe (Oct 27, 2015)

Quick question...        does outside air temperature effect secondary burn (due to less draft)?

Anyways...   I finished up secondary manifold and most of the fire brick...





















I piled on some kindling and got it rolling...    let it roll for 15-20 minutes to get things hot...    shut the primary air down and the secondary tubes lit instantly...   but the jets slowly died and went into lighting the entire underside of the baffle with a deep blue flame 3-4" above the wood...   which again slowly died out after a few minutes and the fire went back to a primary burn...   I do get a good secondary burn while the primaries are open, however it doesn't seem to "jet" from the holes in the secondary tubes except the first few minutes...





No smoke out of the chimney after warm up at all...   so it certainly is burning clean.

With all that being said...    why cant I maintain the "jets" out of the burn tubes?  Can outside air temp effect secondary burn?  Its 55-60 out and raining and I don't hear any draw coming from the secondary valve with the primaries shut...      I can feel a slight air movement there but nothing significant.  I'm wondering if its just too warm out yet...

Do I need to add some type of lining to the top of the baffle perhaps?  I could see the vertical pipe that was low in the firebox had a slight cherry glow but the upper tubes didn't.  Perhaps I need to bring the brick all the way up to the baffle?

I'm open to ideas or should I wait to see what a cooler night will do?

I'm happy with the mods so far as just a kindling fire (no splits) has brought the room temp up 5 degrees and the fire has been out for 15-20 minutes but the stove is still putting out good heat and the automatic blower is still running.

Thanks guys
-Chris

-EDIT-
After some reading, I think its going to take a more significant fire to get  good/continuous secondary combustion...     but still open to ideas...


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## mellow (Oct 27, 2015)

55-60 out isn't very cold to be burning so I would for sure wait till a 40 degree night to get better draft going.


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## Mr4btTahoe (Oct 27, 2015)

mellow said:


> 55-60 out isn't very cold to be burning so I would for sure wait till a 40 degree night to get better draft going.


What can I say...  the wife is cold natured.   Lol


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## Mr4btTahoe (Oct 29, 2015)

Question...

In normal secondary operation, should the flames be jetting out of the holes in the burn tubes or should there just be flame above/independent of the wood in the stove?

I only get the blue jets of flame when I really have the stove cranked up and shut the primary air down completely...   but with the primary open a bit, I can get a normal wood flame...   and a burn above the wood but not coming directly out of the pipes.

So... what is "proper operation"?  What exactly am I looking for in these tests?

I did some playing around tonight during a HOT burn...   shut the primary down and used a hair dryer to push air through the secondary intake valve...    made no difference.

I'm leaning heavily towards heat being the problem.  I am getting secondary burn but its not consistent.  I think I need to insulate the steal baffle plate and get a tighter fit to the sides and back of the stove.  I also think I need to bring the fire brick all the way up to the baffle plate which will be a PITA as its only 3" of space.

Suggestions on material to use?

Am I on the right track?

Thanks guys
-Chris


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## husky345 vermont resolute (Oct 29, 2015)

Why not just buy a new epa approved stove.


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## Mr4btTahoe (Oct 29, 2015)

Because I have $120 in the mods to this stove...   the stove looks great...   has a huge firebox which gets me 12-14hr burns without the mods...    and I love to tinker/fabricate.

I bought this stove last year for $100...     cant really go wrong...

That and I don't have $2k+ to blow on a new stove of similar size just to decrease emissions (which oddly enough, this stove does fairly well at that too when up to temp and not closed down...    figure if I can improve on it without breaking the bank...  why not?)


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## mellow (Oct 30, 2015)

Searching Youtube for "Epa secondary burn"  will get you quite a few videos to look at how it works in newer stoves.

Here is a video of someone modding a fisher for reburn:


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## Mr4btTahoe (Oct 30, 2015)

^^
I'm getting just that during kindling fires and sporadic during regular burn which leads me to believe its a heat issue more then anything.

-EDIT-  I also get secondaries during WOT burn with larger splits...  hard to see but it is taking place but as soon as the primary starts to cool down, the secondaries die out.  Insulation is going to be a must

I may need to change the orientation of the tubes but some research is showing that most if not all stoves that use a steal baffle plate like my setup is using some form of ceramic insulation blanket above the baffle.  When asked, most people claim that the blanket is more important then the baffle itself as secondary combustion wont take place without it.

Any ideas on what would work for baffle insulation?  Anything I could get local?


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## mellow (Oct 30, 2015)

Do you have someone that sells kiln supplies?  If not you want to get Kaowool, search on ebay.


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## begreen (Oct 30, 2015)

One possibility on the secondaries is there is too much air resistance in the pipe. It could be that the intake path is too long and has too many 90* turns for the pipe size. More air would be delivered by a larger pipe feeding the 2 secondary tubes and exiting out of the bottom or back side. That said if there is no visible smoke and the wood consumption is down notably, there's reason to celebrate that success.


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## Mr4btTahoe (Oct 30, 2015)

Its getting there...   slowly but surely.

I went in to town to the local stove shop and they had the 1" ceramic baffle insulation 2' wide...   $15 per foot.  I picked up 2' and started bsing with the owner a bit and was telling her what I was tinkering with.  She claimed that they were the first in the area to offer Silent Flame stoves....   she asked me what model number it was and started describing the stove from memory along with its needed clearances..    said that they were top of the line stoves for their time and performed very well..    over built in a lot of areas...  etc.. etc..

Why didn't I think to call them when I was trying to find info on this stove??   lol

Anyways...   My toys arrived today as well..     I installed the stove pipe probe thermometer..     the fire was already down to coals and registered 250-300 on the Condar fluegard probe placed 20" above the stovetop.

I took the moisture meter out and split one of the large oak pieces I had on the deck..   33%  Ouch.  Some of the small stuff was down in the teens so I'll be mixing it up.  Hopefully I have enough on hand to be 2-3yrs ahead..   we'll see how the winter goes.

I also got an IR temp gun and was playing with it a bit..       My tubes under the baffles at this stage in the fire were 600F...    coal bed pegged the gun which maxes at 1250...     Fire brick was in the 500-600 range.

Waiting for things to cool down so I can get the insulation cut and installed then go from there.  While I was at the shop, we had a look around at their EPA stoves..      Was checking out a smaller Buck stove that used secondary air and other then my tube orientation, I think I'm on the right track.  That little stove basically had a piece of sheet metal on top of the burn tubes with a layer of the 1" insulation.  It also used much thinner wall stainless tubing which would heat up faster...    something to think about as I have access to plenty of scrap stainless material.

I'll find out tonight if that does the trick...   if not, I'll go back to the drawing board on the tube layout.  As you said, it may be restrictive.

More to come.


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## jatoxico (Oct 30, 2015)

I always think its pretty cool when people do this. Wet wood won't help your secondaries that's for sure. Keep tinkering but it's not like my secondaries always fire like a gas barbecue. Often it's more subtle than that. Draft does have an effect so you may want to wait for some cold weather before you decide where you're at.


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## Mr4btTahoe (Oct 30, 2015)

I think we have a winner!

Cut and installed the blanket..








Had an extra fire brick so I split it and sat a piece on top of the insulation on both sides of the flue outlet...

Got a good kindling fire going and let it roll for 20-30 minutes and noticed right off the bat that the flame front was being pulled around the front of the plate instead of around the sides...   the draft was also greatly improved (keep in mind its still 55 outside..)

I went out and picked a few dryer pieces from my pile.  Chucked a few pieces on and let it roll again for 10-15 minutes to help drive out any moisture...   before I even started shutting the primaries at all, the underside of the baffle was rolling...




Right now, its cruising along at 500F...




Primary air shutdown...




And its been rolling steady for 20-30 minutes as of yet...

And the stack...




Nothing but heat waves. 

The heat output is insane...    1 hour in and the room is already rather toasty...   which used to take a several hours atleast.

I call this a success so far.  I'm keeping a close eye on overall stove temps with the IR gun...     Can anyone guess as to a safe limit for a stove that has an air pocket around it?  Stove top is running 270 right now and is still climbing (and that's not in direct contact with the fire box).

If someone can give me an idea on what temps should run or the best places to check on a stove like this that uses a blower and an outer casing around the box, I would be grateful.

Thanks for all the input guys!


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## Mr4btTahoe (Oct 30, 2015)

Secondaries were kicking for about an hour solid and then they died out...   and primary fire took over however the 3 pieces I had in the box were still log shaped...  but nothing but charcoal rolling a nice blue flame off of them...    And that's how it sits at the moment.  Nice small blue flame off of the "log shaped" pieces...

Checked the stack and its still clear as can be.

Flue temp has progressively dropped after secondaries shut down...    Holding steady at 350 19" off of the stove top (which is 22-23" above the fire box)

I'll give it a little while longer and then I'll toss on a few of the dryer oak splits I have and I'll see if I can get any significant burn time now.

After all this...   I'm considering changing how primary air is supplied by sealing off the slots in the front of the doors and piping in air above the glass directed down towards the firebox (poorman's airwash system).  We'll see though...     might not be needed as the glass is clear as can be still.

-Chris


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## begreen (Oct 30, 2015)

Well done. You're having too much fun!


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## brenndatomu (Oct 30, 2015)

Cool project! 
What size pipe did you use for the secondaries? I did something similar, main feed is 1" and then after the bends it goes down to 3/4" for the two air diffusor tubes. Not sure if that is really better or not...
Not on topic, but do you have a 4bt Tahoe? That would be a cool project too


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## Mr4btTahoe (Oct 30, 2015)

brenndatomu said:


> Cool project!
> What size pipe did you use for the secondaries? I did something similar, main feed is 1" and then after the bends it goes down to 3/4" for the two air diffusor tubes. Not sure if that is really better or not...
> Not on topic, but do you have a 4bt Tahoe? That would be a cool project too



As for pipe size, I had a 1" valve so I reduced right after the valve to all 3/4".  I would venture to say that a bit more air certainly wouldn't hurt. 
I let the fire burn down to a hot coal bed and threw on some of the oak splits...   Ran it HOT and still couldn't get the secondaries to cooperate.  I have a feeling moisture content is to blame...   however with the primary air shut down, it looks as if secondary combustion is taking place between the logs...   hot blue flame.  Cant see the stack at the moment to check for smoke so not sure if its burning clean...    Temps are running right at 350-375.

As for the Tahoe...  yeah that's been a long term project of mine.  Its been on the road for a couple years now but its not "done"...  as if they ever are.  I have a full build thread here:
http://www.4btswaps.com/forum/showt...bta-Swap-(Looong-term-project..-well..-sorta)

I'm contemplating changing up the plumbing a bit and running the tubes east/west as I think it would hold more heat in the pipes and keep them burning longer.  The stoves I've seen with factory secondary air are all east/west...   perhaps that's the reason.  I'm curious what the factory hole size is on the burn tubes...    I went with 1/8"..   perhaps a bit more flow would help matters too.  Input?

Either way, stove heat output is through the roof and emissions are all but gone.  I'm very happy with it so far.


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## Corey (Oct 30, 2015)

There are a couple of points to consider with secondary air.

First, you want the secondary air to be as hot as possible when it is injected.  Putting cold air on top of the fire can quench that area and kill off the burn pretty quick.  Ideally, you would have a lot of cubic inches of pipe / space leading up to the air tubes.  This means the air moves really slow in that area, heats up and is injected as hot as possible.  Insulation on top of the baffle and around the firebox also helps hold heat in the combustion area.

Second, ideally, the tubes are thin wall stainless steel.  The thin wall helps the air inside heat even more and the stainless won't 'burn out' the way a thin carbon steel tube would.

Third, east-west tubes work much better as the general flow of the flue gas is from back to front.  The tubes act as 'ripples' in a stream to help break up the flue gas flow and absorb a bit more heat.  Also, the back-most tube can point at the one in front to help heat it, that second tube points at the third, third at the fourth and so on.  They cascade the fire to help heat each other up.

Then, once all this is in place, you need to start looking at the stove like the carburetor of a car.  There is a mixture of air which is 'just right' and gives best performance.  If you let too much secondary air in, you cool the secondary combustion and possibly extinguish it entirely.  Too much primary air flushes through the firebox and cools it off.  Too little of either air obviously leads to smoky / cool combustion just like a rich carburetor.

Generally, the way I go about it is to have the air open to get the fire going.  As you start closing the air down, you will find the stove gets hotter.  Surprisingly, the more you close the air down, the hotter things get.  Then at some point, it levels off and you are 'in control' of the fire.  At that point, you can reduce air further for the temperature you need.  Though at some point, you go too low and it may start smoking.


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## Mr4btTahoe (Oct 30, 2015)

As far as surface area goes for preheating the secondary air, the inlet is on the lower front left of the stove...   goes along the bottom of the firebox to the rear..   right to the center of the box then vertical and out.  Other then running back and forth under the baffle, I'm not sure how I could increase surface area.  As far as temp goes, when the secondaries lit with the dry wood, the tubes were running 1100+F.  As it stands, the baffle and tubes are hovering around 800F...

I am leaning heavily towards changing to an east/west plumbing configuration which may kill 2 birds with 1 stone.  North/South was just easier to work with...  however east/west would not only allow for even heating of the tubes, but more overall surface area in a high heat location.  Currently with the north/south, the ends of the tubes are out from under the baffle and in the smoke stream...   If I ran east/west, I could keep the tubes completely under the baffle which would most likely keep them much warmer.

I've got a few weeks I'd say before temps turn to the point of needing the stove for primary heat...   so I've got time to tweak the design a bit...    but then again, I'm still curious if cooler outside temps (stronger draft) and dryer wood would solve the problem without changing the design...   I'm 100% positive that the oak I through in the box was wet 28%+ but that's what I've got to work with this season which sucks..  next year will be better.

Gives me a good bit to think about.


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## Mr4btTahoe (Oct 31, 2015)

Made a couple of changes this morning to the burn tube orientation...

At least the design made it simple to alter..




To this...




Much more surface area and east/west runs for the burn tubes.  Now the only issue I can see with this is the tubes being different overall lengths...    the longer tube may or may not draw air properly...   wont know until a test fire.

Hopefully this evening, temps will get down low enough to warrant burning as its rather warm out right now.

Anyways..   more to come.  Once this gets dialed in, I'm leaning towards an airwash system.

-Chris


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## Mr4btTahoe (Nov 1, 2015)

Well..  they seem to work well...    how well will have to wait until a colder night.

I'm done tinkering until cooler weather hits...    and then I'll update with how things really work.

Thanks for all the insight guys
-Chris


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## Mr4btTahoe (Nov 8, 2015)

Well...  First cold night after the mods and I must say they work and work well...   Maybe too well.

Primary air is shut down...   Stack temp is running 500...

Stove top (which isnt the top of the box...  There is an air path between the firebox and the top) is running 320...

The doors near the top are pushing 650..  

I kicked the blower on high to get the temps down but I still don't know what is considered safe with this stove.

Am I overdoing it?


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## jatoxico (Nov 8, 2015)

Glad to hear its working. Follow the golden rule. no glowing.


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## Mr4btTahoe (Nov 8, 2015)

Well...  No glowing bits...  Just much higher temps then I'm used to out of this stove.


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## Corey (Nov 8, 2015)

Years ago, I did a time lapse video of the nightly load.  Looks like it topped out at about 880ºF that night.  This was a bit before I had the full secondary air mod and worked to tighten up the stove a bit.  Now I trade a bit cooler temps for a bit longer burn time - unless I'm running full bore to heat up the house.

But, ya, the old iron is probably pretty well seasoned and won't melt until north of 2700ºF, so anything below glowing should be fine.  Heck, even glowing isn't terribly an issue, though does exponentially speed up the oxidation of the steel and lead to eventual 'burn-out'.


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## brenndatomu (Nov 8, 2015)

Mr4btTahoe said:


> The doors near the top are pushing 650..





Mr4btTahoe said:


> No glowing bits... Just much higher temps then I'm used to out of this stove.





Corey said:


> the old iron is probably pretty well seasoned and won't melt until north of 2700ºF, so anything below glowing should be fine


Yup, you're fine...even steel stoves don't start glowing until ~950* or so


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## Mr4btTahoe (Nov 8, 2015)

That's good info to have.

It was popping and pinging at those temps but I think it was mostly coming from the thin steel baffle plate.

Anyways...   I reloaded this morning at 8am with a hot coal bed and the intention of letting it burn out by noon...   It's now 6:15 and the stove is still hot...  Automatic blower still running..   House is still 78.

The load this morning was 4 med. splits.

Very happy with the outcome so far.


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## Mr4btTahoe (Nov 21, 2015)

Just a little update...

Stove and mods have been doing great.  I took some pics this morning to show the outcome...

Primary air closed...    secondaries rolling




Stack output...    0 smoke/haze.




The only negative I can say thus far is that I've managed to warp the outer stove top.  I noticed this the other night when I was loading the stove and noticed a slight gap between the flue and the stove top.  I took a few steps back and sure enough, the top of the stove has warped.  I went on and lit a small fire to check for leaks at the flue mating surface and there doesnt seem to be.   As the stove warmed up, the gap between the stack and stovetop closed.  I dont believe its going to cause any problems but its odd that it happened.

I typically keep a pot of water on the stove top to put moisture into the air...  the pot is pretty large..    could that have caused it?

Anyways...   so far we are staying warm.  Temps are dropping quickly here..  will be in the low 20s tonight..   House is a comfortable 74.
-Chris


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