Smoke rolls out load door - any advice?

Hello coal experts. Thanks for the help so far regarding my homebuilt bituminous burner. Stove has been burning well, putting out more heat than necessary for this time of year. Gotta get the wife to hold back on the fires some.

The advice you gave me for getting a better burn by closing the secondary air is working great - see link below for that thread:
http://nepacrossroads.com/viewtopic.php?t=2110

Now for the next issue. Ever since the first burn (with wood to get some confidence), I get smoke coming out the load door whenever I open it, especially with a fresh load of coal or wood, when most smoke is present. During mid burns, if I open the door, I can see what little smoke is being produced still tends to come out the door instead of the chimney.

I'll admit that I have a 6" diameter chimney. It is 15' high. The stove is in the basement, so I have double wall smoke pipe rising 2' from the stove, then an elbow, 12" of horizontal run to my wall thimble, where I enter a triple-wall tee, and head up the side of the house to the roof. The chimney could use another foot or two of height to get above my roofline (it's 10' from my roof peak horizontally, and the same height as my peak.

My draft seems OK - would be better with 8" I'm sure. But I can really get the fire rolling, and then the draft seems fairly impressive, getting the stove to 600 degrees occasionally. Even then, smoke will come out the door if I open it.

Here's what I'm wondering. Is it possible that I did not leave enough space above the load door opening? I have attached a 2-page PDF file showing a CAD view of the stove drawing. I have about 4-1/2" between the top of the door opening and the top of the stove. I have a baffle plate installed, and the 6" stove collar sticks down into the stove a few inches. My reasoning for building the collar this way was to force the heat to "roll" a little more to get more heat transfer.

To attempt to solve the smoke issue, I tried to reduce my door opening size a little last night by clamping a piece of steel inside the door opeing near the top. It seemed to help some, but it was difficult to tell because I did not have quite the right size scraps.

I'm really hoping the cause of the smoking is not the chimney size (expensive). But if that's truly the problem, then I just need to bite the bullet and go with 8".

BTW - I was looking at Harman's SF-250, and they use a 6" stove collar, and the model I saw has a metal flap that swings down when you open the door - appears to reduce the door opening size. Maybe I need something like that.

Thanks for the advice. I keep saying I'm going to post the plans I drew up, but I'd like to get some of these issues sorted out before I give out the CAD files, to keep others from making my mistakes.

Steinke

Can the baffle be moved more to the front? or Angled back towards the flue exit?

Yes - the baffle just sits loose on two angle irons - I have slid it to the front, but it doesn't seem to make any difference for the smoke coming out. I have not tried angling the baffle.

I have the same issue with my AHS multifuel boiler. I burn Bit coal also. it is only bad when i first load it up. I called Jeff at AHS and he said that a smoke flap would help for sure but the smoke hood ( see pic ) would eliminate the whole issue.

Do you have any form of damper in the chimney pipe?? If so make sure you open it before opening the door.

Try closing the below the fire air supply, then slooowwwllly open the loading door, let the chimney get a chance to increase the air velocity.

I have an air flap on the top of my loading door too. It does help some, but when I was burning Bitum. it wasn't enough when adding a fresh load of coal.

The trick for me was to load the coal very quickly, and get the door closed. I would have two buckets filled, ready to toss on the fire, before I opened the door.

I don't think a 6" chimney is too small, but it may be sooted up already.

When burning Bitum, you can get a soot buildup in the chimney really fast, in a week or two even. Check the cap on your chimney, does it have a screen to keep birds/animals out?? Soot may have clogged the screen already. Did you install a 'TEE' anywhere where an elbow could be, to use as a clean out?? If your Bitum coal is sooting up your horizontal piece of pipe, you may need to make an easy access clean out by replacing the elbow with a tee and cap the unused hole.

So, open the door slowly, let the chimney air velocity to increase,
Close the under fire air when the door is open.
Load fresh coal fast!! have loaded buckets ready.

Check your chimney often for soot buildup.

Let us know how it works out.

Greg L

Thanks for all the replies. For clarification, I don't have a damper in the smoke pipe, so, that's not the problem. I had removed my cap a week ago to try to improve draft. I had also cleaned the chimney a few days ago, and even immediately after cleaning, the smoke issue was no better. I did have some soot buildup after only 3 weeks of use, so this bituminous does not burn as clean as people around here had said. I have not, however, cleaned the horizontal section of smoke pipe above the stove. i need to check that. Good idea on replacing the elbow with a tee to facilitate checking and cleaning. I need to look into adding preheated secondary air to the stove - I've seen the designs on this forum - probably do something similar.

What your replies did confirm was that this may not be a problem with my stove design - just an inherent issue with burning bituminous coal. I used a wood stove with this same chimney, and I'd get smoke rollout when the fire was cold. So I think I'm starting with marginal draft to begin with.

I added a little better temporary smoke flap. It slightly improves the smoke problem, but did not do any miracles. I definitely leave the ash door shut when loading, and further closing the primary draft controls during loading helps only slightly more.

Once I get more familiar with the stove and loading it, I think I can deal with the smoke. Doesn't smoke much at all when the coal bed is old and ready for fresh coal. As long as I get the coal on and shut the door, it seems to work well. If I can just force myself to only open the load door 2 or 3 times per day for reloading, I think it will be fine.

In the meantime, I'm going to keep my eyes open for some 8" chimney and see if that helps. Also considering going straight up the house, through an upstairs closet with 8", instead of elbowing outside with 6". My friend just installed his stove with 8" straight up, and it works very well, rarely has smoke rollout.

The smoke hood mentioned above sounds like it would solve smoke problems, but I can't bring myself to put that beast on the top of my stove - it would not look too great in the family room of the finished basement. Maybe I don't understand how it hooks up or where it vents to.

Thanks

Steinke

Hi Steinke. Yes, taking a 'peek' at the fire 2-3 times a day is almost irresistable.. But the trick is to follow all that you are doing, and slowly open the door.

I have the same issue, I love to watch the fire, it is difficult for me to walk from the shop to the house without making a detour through the boiler building and taking a peek at the fire. Even though it is a stoker fed boiler now. Just like looking at the fire...

Can you hook up a push pull rod to the sliding diverter plate so you can slide it before you open the door to give the smoke a direct path to the chimney?? I have similar diverter plates in my boiler, and have 1/2" push pull rods attached. This helped when I was burning Bitum.

Could you get a torch into the stove and cut the back half of the drop-down or protruding exit pipe off? leaving the front drop or protrusion for turbulance?

Greg L

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LSFarm - Yes, I could rig up a rod on the baffle plate, and even attach a smoke flap to the baffle plate, so when I pulled the rod, it would move the baffle out from below the stove collar, and bring the smoke flap forward to the door opening. I may try that soon.

I think I may also try to torch the back half of the stove collar protrusion off. Hate to move the stove out of the house to do it - maybe if I heat the flue with the torch, I can keep all the torch gunk going up the chimney when I do it. Kind of tight inside the stove, hopefully I can swing it. I'll let you know how it works out. Thanks.

Steinke

Hi Steinke. Can you remove the chimney flue pipe, and work from the top down to cut the lip off the back side of the pipe?? This is instead of working from inside the stove??

Adding a drop to the front of the sliding diverter plate sounds like a quick option. If you just tack-weld it in place to give it a try, then you can remove it if it doesn't work out.

So with a push pull rod on the diverter plate, protruding through the front or back of the stove, you could slide the plate foward to block the top few inches of the door opening, and open a direct path to the flue. Then when you slowly open the door, you should get some extra velocity up the chimney without opening the door enough to let lots of smoke out.

Let us know how it works out
Greg L

That is how my boiler works, it is called a bypass damper. Before you open the door you must slide the damper forward, shunting the draft from the front to the rear. Wait a few seconds to reroute the draft and open the door slowly. It works fine.

Another option would be to add a draft inducer to the chimney flue pipe. Turn it on for loading. But they cost about $150 or so.

Greg

Steinke,
Before you change the vertical chimney, try this interior piping change. Eliminate all 90 degree elbows. We are told that a 90 degree elbow is the same as 10' of straight pipe. I just learned from an intelligent stove dealer, that the smoke actually makes a 360 degree turn in a 90 degree elbow; before moving on.
I own a 95% smokeless gasification wood furnace (http://www.lamppakuuma.com), yet everytime I opened the door to add wood; smoke rolled out. I made my own smoke hood, which never caught all of the smoke. I would even manually close the barometric damper, which created more draft in the furnace; but still smoke would roll out.
I have a two story house with an interior chimney lined with an 8" SS liner. That liner has an insulation jacket above the roof peak, to maintain interior temperature.
I replaced the 90 degree elbow with two 45 degree elbows, and no more visible smoke when I open the door, just a little smell ( the same as opening the door of a coal stoker stove). Believe me I have been opening that door often, trying to prove the theory wrong; but no more visible smoke!

I had already tried to replace my 90 with two 45s, but it did not seem to help in my case. I was hopeful from some other posts that it would do the trick, but it did not. Glad to hear it solved your problem.

Maybe you could help with the 90 vs 45 issue though. I currently have 6" dia. double wall smoke pipe in the house. 24" vertical frm the stove collar, then a 90 elbow, and 12" horizontal to my wall thimble, where I go outside into the chimney, tee up, and then 12' up above the roof. When I tried the two 45s, I just bought two single wall tees and a 24" piece of single-wall pipe. So I came directly out of the stove top with a 45" elbow, which angled my 24" single wall pipe towards the thimble, and then right at the thimble, I but another 45 on and attached to the thimble. It did not solve the smoke problem.

Do you seen anything I could have improved on there? I expected it would help, but it didn't.

I have a smoke flap built and a few other things to try, but haven't done anything until I get the time, and also waiting for the house to be really warm one day before I shut the stove down for a few hours to cut the stove collar that protrudes down inside the stove off. I'm definintely not ready to go to 8" chimney - too much money unless all else fails.

I noticed from a makeshift smokeflap I made, that if I reduce my load door opening to about 100 square inches, I don't seem to have a smoke problem. Without the smoke flap, I have about 185 square inches opening, and it smokes. The makeshift flap is just a piece of 4x4 angle iron bolted to my baffle plate, and I slide it forward to the door opening along the baffle supports. I built a hinged flap that will "give" some to allow more room for loading coal, but haven't installed it yet.

Thanks for the help.

Steinke

Steinke
Since you eliminated the 90 degree elbow between the stove collar and wall thimble, and had no improvement; we will have to go back to chimney basics.
Chimney basics include flue temperature and draft and both are related. Do you use a barometric damper? Did you ever check the draft by using a candle placed in the wall thimble? If not, why not remove the piping and check it, both on a windy and still day.
Tell us about the chimney beyond the wall thimble.

Here are some very good articles on chimneys, even though they are "wood fire" directed.

Read the first one, as well as the two links on the left side.

http://www.woodheat.org/chimneys/chimneys.htm