# Spencer: Adding secondary burn tubes (advice).



## vasonline (Nov 20, 2013)

Hi,

First of all: sorry for my bad english - I'n not native.

- I have placed isolated tiles in our older airtight "Spencer" woodstove.

The insulating tiles have doen a great improvement: lighting the stove is easier.
I think it burns better (not too much smoke is seen)
...and at he end of the day the last logs burn up cleaner.

So I want to do the last step: adding a secondairy burn tube.
- I have made some piping, and made some test photo's.
- I did not yet drill a hole to install the tube. (i held it with my hands in place to make the photo's)

What do you think?

Looks good?

Any tips

- I just screwed the pipes together. Do I need to use some sealing cord? I would imaging it would
melt of the high temperatures.

- I would drill a 3/4" hole and a nut/big washer on the other side to secure it.
- Other places to drill the hole: difficult: this was a boiler model: I do not want to drill into the boiler
section.

Thanks in advance!

*edit: the metal bar in the stove needs to be rewelded (I guess) I am aware*


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## coaly (Nov 20, 2013)

Looks good to me.
No thread tape or cord needed.
Is that galvanized pipe?

Black Iron in the US is "schedule 40" and thicker wall than galvanized. Our galvanized is thin and doesn't last. Double wall black iron for high pressure steam is "schedule 80" here - Stainless is the best to change to if it works !
Not sure if a valve will be needed outside to adjust air. Probably so.


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## begreen (Nov 20, 2013)

The holes appear to be on the top of pipe. I'm concerned that placing them at that location may burn out the baffle. I would rotate the holes to face forward and downward. If you are looking at the end of the pipe this would be at about the 8 o'clock position. This should help stir the gases and perhaps heat better.


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## vasonline (Nov 21, 2013)

Hi Coaly and begreen,

Thanks for your input!
@coaly: indeed it is galvanised pipe. Good tip to use these thicker pipes. Might do that if it works well/wears out

@begreen: excellent suggestion. I kinda did not know what the best orientation was. I tought to point them upwards.
Around 8 o clock sounds indeed very good. The baffle width is kinda small, but it reaches quite high up into the stove's ceiling.

To drill the hole:
I think I'm going to buy a 3/4" drill like this:
(and pre-drill first with a lower diameter)

Good? Beter ways to make the hole for the 3/4" pipe?

http://www.ebay.com/itm/Irwin-91148..._Automotive_Tools&hash=item4d113b2723&vxp=mtr

Greetings


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## PapaDave (Nov 23, 2013)

Be aware that 3/4" galvanized or black pipe is actually 1" outside diameter (or very close to it). The 3/4" is the inside diameter, so you'll need a larger bit.


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## vasonline (Nov 23, 2013)

Hi PapeDave,

Yes, I found that when going to a local hardware store.
I got the right equipment. Tube hole is made Ok.

Everything is installed now. 
(@begreen)
I have adjusted the position of the holes (see pics)

I 'll think I'll also install a valve on the outside (safety function) like other diy'ers did.

Very curious to see how it performs...

Greetings


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## PapaDave (Nov 23, 2013)

Nice.
Curious to see how it runs as well.
Keep us updated, please.
I've contemplated doing this in my stove.


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## vasonline (Nov 24, 2013)

Hi,

First test fires done today and yesterday.
Conclusion: We're not there yet. 

The secondairy burn tube is not igniting.

Well, When I started with a the hot knidling fire, it did ignite. It was really a nice sight to see the flames
shooting out of the holes.
After the kindling fire, I did not see that anymore.

I made some pictures of the burning fire. (after the stove was warmed up)

The flames easily reach upto the tube with the holes, but no flames are coming out of the holes...
Hmm...

I tought of mine: maybe the air is not hot enough? Most of the DIY setups I have see, have the tube routed at least once back-and forth
above the fire. I have only one small piece of tube from bottom to top (see earlier pictures of mine). And it is in a corner, that does get warm, but
of course not as insanly hot as above the fire.

Does that make sense? Or is all the gas already burned?
However: I did a test: I closed the primary air.... the tube did not ignite.

I hope we all can learn from it.

Some Pictures below.
The fire was a bit stronger, then what my camera showed. The wood was burning well.

Greetings


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## vasonline (Nov 26, 2013)

Hi,

I made some modifications to the tubes.
So that they run back and forth one time across the stove top.

But I'm I'm thinking: there is no insulation the baffle plate.
Maybe I can add some?  It would certenly help top get the temperature up.
Ceramic tiles are out of the question: they are too heavy. Or are the very thin types too? (say 0.5 cm)
Insulation rock wool? Over time It would get dirty I guess...?

Thanks for any input.

Greetings


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## Corey (Nov 26, 2013)

There are a few things you need to take into consideration on the tube.  Generally, the tubes will be under some type of insulating baffle.  This helps trap heat and gives the air some time to mix with the smoke.  What is behind the steel sheet running up the back of your stove?  That is somewhat of a unique design I've not really seen before.  It might be hard to make a true 'baffle' plate in a design like that.  Ideally, you would want a nearly horizontal sheet across the top of the firebox and maybe 2/3 to 3/4 the depth of the whole top...the remaining 1/4 is where the smoke/flame would draft up to the flue pipe.

Also, you want the air coming out of the pipe to be HOT.  Ideally, the pipe would be glowing, or nearly so.  You might be able to make a couple runs back and forth across that steel sheet with solid pipe to help pick up some heat, then finally let the hot air out into the pipe with the holes.
Here is a picture of my baffle/tubes for comparison:  https://www.hearth.com/talk/threads/burnin-orange-tonight.106714/  These are stainless steel tubes, so they are pretty thin and heat up fast, but can also stand the heat.  They are orange hot - and in reality probably more orange/brighter than the camera really picks up. There are a few flames coming out the secondary pipe holes (hard to see in the photo) mainly at the front/center.  Otherwise the flames are translucent blue/purple which is indicative of burning carbon all the way to carbon dioxide - complete combustion.  If you have yellow/orange flames, that is actually particles of carbon glowing, which means you need higher heat.  Higher heat will burn the carbon to carbon monoxide - then when carbon monoxide burns, it gives off the blue flame and burns completely to CO2.

Getting the secondaries to 'light off' is always somewhat of a balancing act.  Too much air and it just cools the pipe off and the gasses don't light because they are too cold.  Too little air and you don't get enough 'fire' to make more heat to feed into the reaction.  Sometimes, the wood is just burning so clean (usually toward the end of the burn), there isn't really any smoke to light and the secondaries are somewhat dead anyway.  Though sometimes when you throw a fresh log onto a good bed of coals, they can put on quite a light show!


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## vasonline (Nov 29, 2013)

Hi Corey,

Thanks you for the extensive reply!
It is indeed a unique design. The 'baffle plate' goes up very high into the ceiling of the stove. At the top it is almost vertical.
Behind the lower part of the baffle plate is the chimney exit hole! 
You can lift out the baffle plate to gain access to it. 

I am thinking that I could add 2 or 3 insulating firebricks on the back of the baffle plate. I measured it, I think they could made fit.
Ony the lower portion that it. Up to around the tube of the secondairy air.

Meanwhile I did route the burn tube back-and-forth in the top. (but not behind the baffle plate).
The air should at least be a lot hotter.
Tomorrow we'll do a test burn.

Greetings


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## vasonline (Dec 1, 2013)

With the tube running back and forth: it worked!
I have added some pictures.
You can see it in the top. In real life it is much easier to see the flames shooting out of the tubes.
The last photo shows the tube going back and forward.

The holes are now 4,8mm wide.

The secondairy burn is mostly used in the first phase of a new log. That gradually stops when the wood becomes more charcoal like (and burns with less flames).

Maybe I should also add some insulation tiles to the baffle plate? (lower part)
it would certainly help to keep the temperatures high?
Currently the sides and back are insulated.


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## Corey (Dec 6, 2013)

Some baffle insulation will help keep the heat in the fire - of course if you overdo it, you can't get the heat out of the stove.  Most modern designs have the insulating baffle with the idea of getting all combustion to take place under the baffle, then the superheated flue gas wraps around to the top and transfers heat to the stove.

Another thing to keep an eye on is the air supply.  I was really amazed at how little air it takes to keep my secondaries going.  I originally built two slots for air intake - they were about 1" x 4" each (or 25mm x 100mm).  But when actually running, I only have one slot open - and even then it's only about 3/4 inch or 18mm.  Any wider than that and the stove starts to cool down due to having too much excess air going through it.


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## Motor7 (Dec 7, 2013)

Vasonline, good job on sticking with it and making it work. I still have to add secondaries to my shop stove and I know I can make it more efficient.


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## vasonline (Dec 11, 2013)

Hi,

Thank you for the kind words.


Greetings


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## Frank625 (Dec 11, 2013)

That is not galvanized pipe I hope. Fumes can be a problem.


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## brenndatomu (Dec 11, 2013)

^^^ The galvanized parts outside the stove likely will never get hot enough to cause fumes, the stuff inside, looks like it is already burnt off!  Those fumes just went up the chimney with the rest of the smoke anyway. No big deal...
Nice work vasonline!


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