Re-constructed fire box design

I tried the heated secondary air last year it worked but the pipe that runs through the fire only lasted about 48 hrs before it was looking pretty bad. It did work it sounded like a torpedo heater was my stove. I think cast iron would be the way to go if not I would use 316 stainless. The problem with stainless is it will probably be around $100. Plus even stainless may not last in that enviroment.

Instead of steel or stainless how about cast iron? The end section of a old cast iron radiator with exit air holes drilled as needed.

I think tubing would start to disappear in a day or two. The thin wall will not take the heat like the mass of a solid bar. The bar can pull off heat from the top 30% and dissapate it to the larger lower mass. The heat will blow right through the top of the tube.

Thinking about this grate thing, do you think square bar would work well?

Greg,
The cap on the inlet pipe is not permanent. It can be taken off at any time. I have the pipe threaded and capped so if I do not want the cool air coming in when I start a fire I can cap it off. I wasn't sure if it should be wide open all of the time especially when a fire hasn't been started and the air not being heated up. Am I wrong in this thinking and does it matter if the air is not heated when first starting a fire?

....Rich

Hi rich, I think you will find that you can't get much help from the secondary air piping during an initial fire-building. You need a lot of heat to light off the soot and volitiles from the coal.

Maybe when you create your initial wood fire for the coal fire to be built upon, it may heat up the piping enough. You won't get any airflow through the pipe untill the door is closed, and the cap is removed.

You may want to hook up the outlet [air, not vacuum] side of a small shop vac to the end of the pipe while loading fresh coal on an established fire, this may burn off some of the smoke. I'm not sure.

BUT this may CAUSE more smoke coming out the door, if the chimney can't draw enough to take on the extra volume of air. In my boiler I had to turn off all added air, slowly open the door, and very quickly add the Bituminous coal, because it started to create huge volumes of smoke almost immediately. Then I closed it off and turned on the fans. AND LEFT it ALONE for 30+ minutes so the volitiles would burn off and not burn in my face [backfire] when I opened the door.

It's kind of frustrating, 'cause I like to watch the coal catch and start burning, but you just can't with Bituminous. WAY too dirty/messy, at least the coal I was burning.

Greg L

Tigermanrich - Just curious how the secondary air worked. I built a very similar secondary system for my handfed. I hadn't seen this post yet, but I came up with using 3/4" black pipe and running it through the stove almost exactly like you did. But I just couldn't bring myself to cut a hole in the front of my stove yet, so I put an elbow on the pipe at the front of the firebox and tried to draw air from the under the grates, inside the ash area. It did not work, only saw a few small flames near the center of the manifold at the highest burn/draft stages. I'm assuming the pressure/vacuum is not correct to draw through the pipe. Also, the pipe looked terrible about 2 days later, very short life. Got some stainless to try now.

How did yours work?

Steinke

Steinke,
It worked great for the first week!! When mine was working I had no bridging what so ever and the coal burned down completely to fine ash. After a few days the wall of the pipe kept breaking down and got thinner and thinner until a hole formed and then it broke in half. I thought that steel was all one piece and didn't have soo many layers!! Boy was I wrong. I had to rip it off and plug the hole in the front of the stove. The stainless steel pipe from what I hear is the best route! I would like to get me a few pieces myself, but herd that it is very expensive. I think one reason your idea isn't working soo well is because you are having air coming in from the ash door being pulled up through the bed of cools up your chimney from the draft and there just isn't enough air being pulled in for your secondary air pipe to work. Maybe if your had some type of forced air being pulled in from your ash door this idea may work, but like you stated I don't think that you have enough air pressure for this concept to work. Unfortunately I think that you may want to break down and put that hole through your newly built stove. I think this is the only way that you may get this secondary air system to work. I have plans this spring to change my grate system to what you have. I like your grate system and think that it will work 100 times better than what I have. I have way too many rocks and clinkers built up after about 2 weeks of burning where my grates are completely blocked from getting any air up to the coal bed. I have to let the fire burn down, clean it out completely and start a new fire. How is your grate system working for you? Do you have any problems as I just stated or is it a nice continious burn with no problems? Good luck with your stove and hope that the stainless works a lot better for you.

.....Rich

Glad to hear the secondary system worked. I have a piece of stainless I may try. Gotta get a hole saw and bite the bullet and cut the hole. I have secondary air that enters above the fire through a draft slide in the load door, but it just isn't preheated enough except during the hottest part of the burn cycle.

My grates are working fine. I do get a few chunks of hard ash, an occasional clinker, and a few rocks, but I can go for several weeks or more before I clean the grates. Up to this point, I've been killing the fire every week or so to make some mods to the stove, so I've taken the opportunity to clean it then. Seems like lately I've been into some better coal, so I'm not getting much on the grates. Our western bituminous is excellent burning. No swelling or bridging that I can see, no crust to break. Just lots of volatiles at first, then a nice clean burn.

Grates have not warped or corroded at all in 3 months of use. I did not use epoxy-coated rebar. The only problem I see with my grates is that some of the chunkier ash tends to "ride" on the grates even when shaken, mostly the ash that's closest to the grate axles. The ash near the edges of the grates (furthest away from each axle) falls through fine. Might be better to make the fingers of the grates "mesh" together, that is offset the shorter pieces of rebar on every-other grate. That might tend to mix things up a little better. If that doesn't make sense, let me know. Also, due to some ash funnels I placed below the grates to better catch ash in my pan, I have relocated the connecting pin system for the grates, and I now use the center truss to connect the grates together. It works fine.

Good luck. Let us know how the grate rebuild goes when you get to it.

Steinke

Tigermanrich wrote:Steinke,
It worked great for the first week!! When mine was working I had no bridging what so ever and the coal burned down completely to fine ash. After a few days the wall of the pipe kept breaking down and got thinner and thinner until a hole formed and then it broke in half. I thought that steel was all one piece and didn't have soo many layers!! Boy was I wrong. I had to rip it off and plug the hole in the front of the stove. The stainless steel pipe from what I hear is the best route! I would like to get me a few pieces myself, but herd that it is very expensive.
.....Rich

How about using cast iron for the pre-heated air? I'm thinging one end section of a cast iron radiator mounted above the fire. Drill holes in the cast iron where needed for air exits. Intlet air would be through the threaded pipe tapings. You would have to plug the nipple openings that normally connect each section of the radiator to the next.

Yanche - I don't know. Is it enough preheating if the pipe doesn't lay in the coalbed? Is just running the secondary pipes/radiator through the air above the coal enough preheating? It would be a cinch to just run some pipe somwhere else, like around the top of the brick retainers and then exit out a manifold above the fire. But I'm doubting that would be hot enough. Anyone else tried it?

Steinke

The hotter the better. I ran my secondary air up the firbox side of the firebrick, so the coal fire was right against the tube, it ran red hot, and the flames were very impressive over the fire, especially when loading fresh coal with lots of volitiles, made for a real 'blow-torch' effect.

Greg L

Well, I don't know what I'm talking about when it come to secondary air designs. What I was suggesting was an alternate material, cast iron, which might hold up better than the steel pipe. I had a welder friend that made a natural gas furnace using a small cast hot water radiator with holes drilled in it as the gas manifold. It worked well. Seems to me using cast iron from a radiator or automotive engine exhaust manifold might get you the durable material that's needed.

The cast iron would be a much better choice, it has a several hundred degree advantage on steel.

Here we go again....During the summer I had some free time on my hand and decided to do another firebox design....Never ending. I'm thinking that this will be the winner. First off I made the grate system like the harman stoves (outside handle and shaker grates) I have a secondary air system that use the sides of the false inside walls and welded in place 3 pieces of regular black pipe above the fire. The air is coming from 1" holes on each side of the front of the stove. I also have a movable HEAVY DUTY baffle that slides for when you feed the stove.

more pics