Wood/Coal Stove and a Baffle

[venator260]

I'm hoping that I get the correct intersection of knowledge here. I feel as though on NEPA Crossroads, the prevailing opinion would simply be "don't be an idiot, burn coal". I want to utilize the woodlot behind my hose, however; so here I am.

So I've posted here in the past about my ownership of a wood/coal combo Penn Royal (pictured below). The baffle on this one is present, but quite small. I've read numerous places that a good way to modify an older stove to squeeze better performance from them is to add/extend the baffle. Over the weekend and into this week, I had a small amount (200-300 pounds) of nut coal. I burn down two loads of wood by mid afternoon and had a nice (wood) coal bed, and began to burn the coal. After re-learning my stove for a day or two, I've decided that the black rocks will keep me much warmer when temperatures go below a daytime high of about 25 degrees. This is mostly due to my ability to keep the stove at about 650 degrees all through the night, impossible with wood.

I say all of this to ask the question: Can I make the baffle bigger without losing the ability to burn coal should I want to do so? I understand that I would be better served (burning wood) with a new stove, and I have one in my sights, and will have one in a few years. Extending the baffle will be a no-cost mod, however, as my dad can make it with scrounged steel and likes doing this sort of thing.

 

[coaly]

Coal requires much more oxygen through the fire bed than wood. The baffle is a restriction to flow in the firebox similar to a damper in the flue pipe. So your question can only be determined by how much draft your chimney creates and if that will be enough air flow through stove with added restriction. It's not a stove question, it becomes a chimney question. If too much restriction, it will be very sluggish with coal or go out. You can tell right away if flames above coal are very small and not a few inches tall with about half air. Full air or open ash pan door should result in flames all the way to the top. Too much baffle will give you flames like it's just cracked at idle no matter how much you open air. Generally, a coal only stove is designed for an exact amount of draft regulated with a barometric damper. They normally can't be modified since the flow through fire bed is calculated for air above fire for secondary ignition of coal gas. You're not only changing primary air, you're changing secondary as well and adding turbulence above fire that is better suited for wood.
Wood is much more forgiving and doesn't care where the air comes from, so you can baffle down (smoke space above baffle that exhaust flows though) to the same square inch of the chimney flue. That should be the same size as stove outlet as well. That would be maximum baffle for an insulated indoor chimney the same size as stove outlet. The more heat the flue requires, as in larger diameter, outdoor, masonry, the more heat it needs and the larger the smoke space. Angle of baffle is also important, it should not be level. About 30* on a step top stove seems to work very well. If you can make it removable for coal, that would be best.

I usually have enough free standing dead to burn over a winter in a wood stove, but when I don't, I light the Hitzer coal only and take a welcomed break from the wood for a while. I'm a firm believer in a dedicated coal stove and a wood stove in the kitchen that includes an oven and hot water tank. They are my only heat sources and one is always a back up for the other.
Here's a thread you can adapt to your stove for burning wood;
https://www.hearth.com/talk/threads...d-fisher-more-heat-less-smoke-under-25.74710/

 

[venator260]

I thought perhaps that you would reply

My coal experiment seemed to tell me that I have a decent draft. To avoid baking myself and my wife out of the house, I had to damper down my coal load pretty good, just about as far as I would on a load of wood in the same stove after I got it going. I did have two problems with the fire nearly going out, but I think this was because the shaker system on this stove isn't the greatest and I wasn't getting the ash cleared from the bottom of the load. Another time I didn't have enough coal in the stove to cover all of the air holes around the sides of the grate and I think air was going around the burning coal instead of through it. This all with what looked to be nut sized coal with a good amount of fines in it.

My other though was as you mentioned here, make it removable so that I can pull it out if I want to switch to coal mode. I would have to do some thinking on this, as I would expect to switch from wood to coal while the stove was still hot. Tossing coal on top of a wood load that was pretty much charcoal but could still be coaxed to flame by opening the ash pan door seemed to get a layer of coal burning quite good for me this weekend.

The system that I would Invision would be me looking at the forecast a week at a time. If I saw nights in the single digits with days not above freezing, coal goes in on Sunday and I burn it for the week, then reassess the next week.

Again, I know that this wouldn't be a perfect system. However, I'm attempting to utilize the resources I have on hand for right now with the plan to get a newer stove in thd future. Im leaning toward a cat stove because of burn times, (either Blaze King or Ideal Steel). Coupled with some insulating projects I have to do, that should serve my needs, even on the coldest days.

 

[coaly]

Yeah, maybe a section in the center that slides open or a hinge that drops to allow direct flow out with coal. Just like a CAT bypass to allow preheat before directing flow through CAT.

Any shaker system has deficiencies in areas where they won't always clean well. Once you learn where to clean a little manually you get a more even fire. I've found if I only shake it for a few days, heat output is lower and more shaking is needed daily. (A couple times during day instead of once morning and once night) When you clean it good from the bottom until glow is even everywhere, it gives empty pockets on the bottom that tends to clean itself as the ash falls through instead of accumulate under the fire. My house temp is about 2 degrees warmer in the morning (room farthest from stove) when I take time to clean it from the bottom each night. When you clean a fire in a larger firebox like a locomotive, the grates are much wider like plates it burns on, that rock, or tilt only, so it only shakes out between each plate. That is the same thing you get on a smaller scale in a stove with rocker grates, where the ash stays piled on the grate and only falls easily directly between them. My Gibratar with grates more like rock crushers were better, but if you over shake them, a piece of coal can get caught between them and have to burn out to be able to shake again. They all have their faults. I think the European type with a slicer knife cleans the best through little slots across the front, but ash leaks out around the slots with little doors on them when running the blade in and out. The coal brand has a lot to do with it too. Blaschak seemed to make a lot more ash in my Hitzer than other coal, and that's the brand the local Hitzer dealer sells. He claims his customers like it. After trying a ton, I never went back.
I can shut my air down to a crack and turn fan off for warmer days and not overheat my place. It has never gone out, but I have a 6 inch insulated Dura-Vent metal chimney. This is the first year I've burned coal with a manual damper. Barometric keeps it much more even with only a couple degrees fluctuation between shakes. Since we've had barometric dampers on this chimney for years, we know when the flapper was open slowing the draft for the amout of fire we had, so I think we're close to where it should be most of the time. I wouldn't try it by guessing if I never had one on the venting system.

 

[venator260]

I'll have to experiment and look around. Some of the baffle threads through the Fisher forum has given me some food for thought.

The shaker on my stove is a round 10 inch plate in a 12 inch slider. I can rotate the plate and slide it back and forth. That would work wonderfully, except there is a two inch area all around the above system that's stationary. So I found that if I didn't dig the ash out around the sides, I would have fire only in the center of the stove. So by the end, I learned to keep the fire pretty robust so that it could handle being messed with a bit. Even with the inability to burn down too far, I still got 9-10 hours of heat that was good enough to keep about 1800 square feet of poorly insulated house (including basement) comfortably warm. The back corners never did keep alight though. I'd have to fiddle with that some more.

Oh well. For now my coal experiment is over. I'm out, and its warmer outside. My wife also doesn't see the point of paying for heat when we have free access to firewood. Shes not the one to fix the fire though.

 

[coaly]

Are you sure you have all the coal conversion parts? They should set on that shelf and make angled sides with slots for air to become a firepot. It makes the grate much larger and funnels the coal to the grate.

 

[venator260]

I thought I posed a reply. Apparently I didn't.

I think I have everything. This was my grandfathers stove, and he never threw anything away (to the level of old car parts and the old coal stove he had before this one). So I would think that if he got parts with it, he would have kept them.

In addition, the sparse details I got from nepa crossroads seems to make it sound that others have the same problems. My fire was out this morning, so I snapped a picture of the crate and baffle.

 

[coaly]

That's the angled parts that make about a half firepot and as good as it gets in yours. The dedicated coal burners have those slots all the way around. Yours does direct coal and air flow through grate.
Normally called "liners" in a coal stove or conversion parts in combination stoves.

Two things with coal;
Make sure you're not opening secondary air too much at top. It only needs to be cracked. Too much allows indoor air to slip up chimney over fire cooling flue - reducing draft.
Your picture appears to have 6 inch pipe increased to 8. If you have more than 15 feet from stove base to chimney top, that's too much 8 inch diameter area to heat with coal. You will lose draft overnight as it cools. It has to have an insulated liner. You're only going to have 100* to 150* f. going into chimney with coal. The stove probably requires the same size as outlet all the way up. Starting a fire with wood puts plenty of heat in the chimney, and once a coal fire is established drops considerably. If you have too much flue area to keep warm, it will slowly die.

The reason I came up with 15 feet is that is the height most stoves were tested with. I always had a 6 inch insulated flue on all my coal and wood stoves, and loaned my Gibratar to tenants in one of my rental homes. That is a 6 inch stove now connected to an 8 inch masonry chimney, but it is on the living level and the chimney top is about 15 feet from hearth pad. It works well, but I wouldn't go higher since I see the difference in how it worked burning harder if it needed with the 6 inch all the way. It slowed it down so much that another 5 or 10 feet would kill it.

With that grate, you may be better keeping the fines out so you have more air space between coal pieces. Even mix with some larger pieces of "stove" size? If you have a chimney issue with weak draft, it requires more air space for less resistance though fire bed. Only a manometer at the flue collar will tell you where to set draft preferably with a barometric damper.

 

[venator260]

Good to know I have the right grates.

My stove has a 6 inch pipe from the stove to the chimney, and it attaches to a 6 inch extension of the liner. My grandfather had the chimney lined about 10-15 years ago. There is roxul insulation between the wall penetration and the old clay pipe. The newer liner is oval shaped, not sure of the dimensions. In any case, draft didn't seem to be a problem during my coal experiment, even though its a longer chimney ( basement to above the leak of the roof, 2 stories plus attic up) id say about 20-25 feet) As I said, I had to shut the air down pretty tight to prevent overfiring, almost where I put it with wood.

Air through the grates did seem to be a problem though. And come to think of it, the coal that I did lose the fire with did have a good bit of fines and dust it in. A feed sack full of what I had was muddy, so I washed the dirt off of it, which also got rid of the dust. This coal seemed to burn better. Perhaps when I buy some coal I'll get a bit of stove coal to mix in and play with the ratios. A local place will bag it up for me, about 80 pounds to a bag. Their price was pretty good too. Worked out to about 250 a ton.

Now I just have to convince the wife I need to purchase more coal. She cites the fact that I have all the wood I could ever want growing behind the house. Which is true, and despite this stoves shortcomings for burning wood, it keeps the house pretty warm. However, I have a new toy to play with in the form of learning how to maintain a coal fire that has the happy side effect of keeping us warm.