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

[Mr4btTahoe]

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?

 

[mellow]

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/

 

[Mr4btTahoe]

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

 

[begreen]

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.

 

[Mr4btTahoe]

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.

 

[coaly]

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..

 

[Mr4btTahoe]

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.

 

[coaly]

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;

 

[Mr4btTahoe]

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.

 

[Mr4btTahoe]

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.

 

[coaly]

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/

 

[Mr4btTahoe]

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!

 

[Mr4btTahoe]

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.

 

[Mr4btTahoe]

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.

 

[Mr4btTahoe]

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.

 

[begreen]

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.

 

[Mr4btTahoe]

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.

 

[Mr4btTahoe]

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

 

[begreen]

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.

 

[Mr4btTahoe]

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.

 

[Grisu]

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.

 

[Mr4btTahoe]

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.

 

[Mr4btTahoe]

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?

 

[zig]

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.

 

[Mr4btTahoe]

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.