home built secondary burn chamber

With some fab skills could you add a chamber to older style wood furnace to improve emissions?

JH

To a non boiler wood stove or a boiler type wood stove???

Non-boiler wood furnace.

From what I've seen in photos both here and on the net the secondary burn occurs when the smoke travels through a heated plate with slots/holes, I'm sure That I've over simplified this but I going by photos over the net.

Could you not divide the firebox with plate about 6" from the roof to create a secondary chamber?

If I'm nuts let me know!

Pics of the internals of non-catalytic high efficiency stoves/furnaces and boilers would be very helpful.

Thanks, Jeff

Hey JeffHK454 , i just caught your PM. I'm sure you could build one to work on your unit. Stove company's do many test and arangments to get there design just right and to do the best job. Some secondary burn chambers are tubes and some are plate baffles. Here are some in my EPA stove that i had posted on another thread here. The big thing about secondary burn chambers is all the smoke and un burned gasses that go up the stack are turned into free heat for you. normally secondary burn chambers run at temps of up to 1100° the better one are made of stainless steel to take the extra heat. You'll need to line most of your fire box with refractory bricks ( stove bricks ) to keep the heat to a higher temp inside your fire box. The secondary burn chamber will need it own air supply so it not just a baffle sitting there. I post some pic and add some links.

http://chimneysweeponline.com/hocats.htm Here is a web page showing a cut of a stove with a secondary burn chamber. http://www.adamsstove.com/wood/pacific/pacific.htm another good read http://www.thefarm.org/charities/i4at/surv/woodburn.htm http://www.alternateheatingsystems.com/woodgasification.htm That should get you started.

Rspike said:

Hey JeffHK454 , i just caught your PM. I'm sure you could build one to work on your unit. Stove company's do many test and arangments to get there design just right and to do the best job. Some secondary burn chambers are tubes and some are plate baffles. Here are some in my EPA stove that i had posted on another thread here. The big thing about secondary burn chambers is all the smoke and un burned gasses that go up the stack are turned into free heat for you. normally secondary burn chambers run at temps of up to 1100° the better one are made of stainless steel to take the extra heat. You'll need to line most of your fire box with refractory bricks ( stove bricks ) to keep the heat to a higher temp inside your fire box. The secondary burn chamber will need it own air supply so it not just a baffle sitting there. I post some pic and add some links.

Click to expand...

Thanks much for the info and pics, I was watching the "smoking boiler" thread which made me think about improving my current set-up.

I could add the fire bricks and fab/install the plate but the secondary feed air is still unclear,it lets air in up high above the chamber plate? Is it a "tunable" type vent that you set by looking at the fire and making adjustments?

Thanks, Jeff

I did some reading on one of the links and it looks like the secondary feed air is going to be the stumbling block. How I can add controlled and heated air for the secondary burn is getting complicated, if anything I've learned a little!

I have thought of the same thing you are fora long time. I have a forced draft option for my wood furnace, Its a US Stove Hotblast Wood/coal Furnace. My forced draft blower is on the back of the furnace right under the flame baffle. It goes into the stove, then from there its pushed through a piece of channel, which blows the air out the sides. I was thinking about adapting 2 pieces of heavy pipe one on each end, and drilling alot of holes in the pipe. Then run the pipes right under the baffle and have the holes facing the fire. This way you always get more secondary air to the fire. By the time the air goes through these tubes, it comes out hot, which then is easier to ignite the smoke. When the fan kicks on it pushes heated air directly on the fire. Now for coal this would do no good, but for wood, it would really help. These 2 tubes wouldn't take up any room in the firebox. I think it would work, and I have 1 1/2 OD 1/4 wall tubing, which would stand up to the heat. This would direct heated oxygen above the flames, which would help to re-ignite the gasses. I have also thought of putting a piece of steel on the baffle so when the smoke rises, it doesn't go apast the baffle right away, and keeps it there a little longer to be burned. These were just some ideas I have thought of. I have already rebuilt the inside of my furnace, its around 20 years old.

I Have a two part plate that I plan on installing that will hopefully slow the escape of smoke and improve the burn efficiency. The flue opening on my furnace is in the top rear of the fire box and makes for a very straight shot out , the plate will divert the smoke back toward the front of the stove for a longer trip out. I might also angle the plate down in the front to create a "pocket" in the rear of the stove further slowing the exit of gases.

I'm also going to line the sides with fire brick to increase the inside temperatures.

I'm not going to do anything that's not reversible.

I have also considered a home brew forced draft but this is something that only works during the "heating" cycle and you still end up with a smoldering fire.

I'm also in the process of making a fire monitoring system which uses both a fire box and flue probe to keep me informed of temperatures that are too low or too high. This little system will have a central "logic" box to trigger alerts when the fire is cooling and needs to be fed or if a very high flue temp signals a potential chimney fire.

Just some ideas , Jeff

I also have a US Stove 1600M that heats like a mother but needs help with efficiency.

With the forced draft you always have fresh air entering the rear of the firebox which aids in the combustion. Whether its running or not. It really helps. I also have a single baffle, with the exit at the rear. So its a straight shot like yours. I do have firebrick. The only thing is the furnace may not be made for the excess heat, the gases burn at very high temps. If you have luck with your design, send a pic, and let me know how it works. I've been looking for ways to improve mine.

laynes69 said:

With the forced draft you always have fresh air entering the rear of the firebox which aids in the combustion. Whether its running or not. It really helps. I also have a single baffle, with the exit at the rear. So its a straight shot like yours. I do have firebrick. The only thing is the furnace may not be made for the excess heat, the gases burn at very high temps. If you have luck with your design, send a pic, and let me know how it works. I've been looking for ways to improve mine.

Click to expand...

The forced draft is always running , do you manually turn it on when you build a fire? They sold a kit for mine but it was switched with the thermostat that turns the blower on.

I'm also not shooting for 1100 deg. with my modifications, just more than the 325-375 I get now. From what I've read on the net any controlled temp range from 400-500 is very good for a non-high efficiency wood burner.

I also have fire brick on the top and down the sides at a 30 degree but I would like to add vertical rows down both sides.

I also looked at the US Stove site for the make-up of the Hot Blast forced draft kit but the pic is so tiny I can't even rip off there idea.

JH

The draft kit is electric, correct ?

I set the forced kit at lets say 74 degrees, and I set the gas furnace at 68 degrees. If the house needs heat, the thermostat on the forced draft kicks on and loads the fire with air, it gets hot, the furnace blower kicks on and the house is warm. When the house hits 74, the forced draft shuts off. For the forced draft to get air, there is a damper on the fan itself. It stays open so even if the forced draft shuts off, air still enters that 2 1/2 inch hole and helps feed the fire. Its a squirrel cage fan. I never got any cresote accumulation at all in the chimney last year. And in the dead of winter when the wood furnace is running, there is no smoke 15 minutes after loading. It did drop the burn time down to 6 to 8 hours, but burns alot hotter and cleaner. I load 4 to 5 logs at 9:30 pm open the dampers for about 20 minutes then shut it down, I do keep the ash drawer damper open, and I keep the damper on the forced draft kit open. That way I dont starve the fire and 5:30 am the furnace is full of red hot coals, throw on wood and away I go. The forced draft kit has a relay, limit control and a junk thermostat. I put a programmable digital thermostat on mine.

Thanks for the clarification.

When I bought my furnace the sales guy was uninformed about the forced draft kit for my model so I shied away from it but I might rethink it.

It sounds like it does as advertised.

JH

One other thing, I hear it works good with hard coal or soft coal. So if you ever decide to burn coal it would help you there too. I burned some hard coal last year and I was first told to turn it off when burning coal, but im gonna try it this year.

Whats the going rate on coal and where do get it?

I've burned it in fires while camping/offroading in Kentucky and Tennessee but have no experience with it as home heating fuel. We would gather a couple
5gal buckets of it and dump it on a active wood fire for something different.

I actually like the smell it gives off.?

JH

I get it around here ashland county from the amish. Last year is was 185.00 a ton picked up, Not sure of it this year. The hard coal I get has no smoke, no odor whatsoever. Burns well over 12 to 14 hours very hot! If it was washed, you could touch it all day and stay clean as could be. Hard coal is extremely difficult to get going, but once its lit, its hard to go out. If you burned hard coal your neighbors would never have a clue you were burning anything. Also there is no need to sweep your chimney, because it burns so clean. Its close to 90% carbon.

I would like to improve my summeraire furnace as well. Would a stainless barbeque burner work for the air tubes?

Thanks

Nope, You would melt them in two.

Bummer, How about cast iron BBQ burner? I've seen those available.

I modified mine last year, it works very well.
here is a sketch.
The blue are fire bricks added to increase the flame travel distance.
The red is iron pipe added to allow air to preheat before entering the chamber through holes drilled into it.
I'll post some pics later tonight.

here goes.
it is tough to get pics inside the firebox




here's a couple action shots