Optimum Flue Size

 
Josh H
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Post by Josh H » Mon. Oct. 27, 2008 8:27 pm

Hi, thanks to all your great advice my new Hitzer 354 (handfed) is working great. I am however getting some smoke and smell when reloading, using Bit coal and wood,its pretty offensive. My stove is near the staircase so I could be getting some reverse draw their. Stove has a 7" flue which I had to reduce to my existing 6". I currently have 18' of 6"class 'A' stainless, and 2' of black interior pipe. This setup worked great with my wood stove, however I would not have been able to use it during these mild temps, 35-60 F. I am looking to build a masonry chimney in the near future, the new chimney will have the same effective height of the old one. 30' from footer to the top, 18-20' usable height. My current and future setup exceeds the guidlines for being over the roof peak. I am not sure whether to use a 8X8 or 8X12 flue. My shop has a 8X12 which works great so that is where I am leaning. My masonry supplier is very helpful but unknowlegeable, he still can't understand why anyone would want to burn coal.
I am also uncertain as to the advantage of having the chimney inside the home. One of the wood burning websites has an article called "The Evil Outdoor Chimney", however from my lurking around here most of the pictures show a outside chimney, which would be a whole lot easier.

Thanks

Josh H


 
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cArNaGe
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Post by cArNaGe » Mon. Oct. 27, 2008 9:00 pm

Woodheat.org talks about the evil outside chimney. The reason exterior walls don't work as well is because usually 3 sides are outside. But they do work. Interior chimneys stay warm all around so they draft better. Plus they can give off a little heat, if they are exposed.

As far as what size flue. I just took an 8x12 out and am replacing it with an 8.5 x 8.5. the 8x12 had three thimbles for three woodstoves running at the same time. For most appliance's 8x8 is fine. Unless you get into the bigger Stoker boilers that have 10" pipes.

 
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rockwood
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Post by rockwood » Mon. Oct. 27, 2008 11:44 pm

cArNaGe is right on here.

For many years I couldn't understand why my folks chimney would down draft and draft poorly at times until I understood that pressure differences (stack effect) created by multi level houses competes with the draft of an exterior chimney like the one my folks have.

I personally would not install a chimney outside the pressure envelope of a house because of the potential draft problems it could have. I know by experience that a properly installed inside chimney will always make draft and an exterior one may or may not.

Be sure to use CO monitors just to be safe.

 
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LsFarm
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Post by LsFarm » Tue. Oct. 28, 2008 2:45 pm

I'd go with an interior chimney, 8"x8", it is too hard to keep an 8x12" hot enough to draw well

With Bituminous coal, you need to clean the flue and chimney often,, the soot build up can become very restrictive very fast... Check your flue now, then every two weeks, and see how fast it is getting obstructed, if it is at all.. then check every month, etc,, just to monitor your soot buildup.

Greg L.

 
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Post by Rob R. » Tue. Oct. 28, 2008 3:10 pm

The flue in my chimney is pretty big and I've noticed that my Hitzer can spill a little smoke smoke/odor into the room if I open the door with a real low fire. My solution: Open ash pan door and get the fire good and hot to warm the stovepipe/flue before opening the door to reload.

 
Josh H
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Post by Josh H » Tue. Oct. 28, 2008 7:37 pm

Thanks for the advice.
An 8X8 flue sure looks easier to build than the 8X12. Are you guys pretty sure that the masonary will draw better than the 6" stainless?
I can get the stove melt-down hot and still have the smoke spillage, that is what makes me wonder if this is a chimney issue or a stove issue.
I had the chimney very clean when I put the stove in a couple weeks ago, I'll let it burn out and re-clean and inspect.

Thanks, Josh

 
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Dallas
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Post by Dallas » Tue. Oct. 28, 2008 8:34 pm

Is your house too tight? Open a window and see what happens.


 
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Berlin
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Post by Berlin » Tue. Oct. 28, 2008 8:41 pm

there's something about the smell of bituminous coal and wood burning together that's nauseating, whereas one or the other burned separtely smells completely different and imho, not bad at all.

as far as the chimney issue, I can almost say with a certainty that the 6" chimney is your problem. it has been my experience that an 8" or even a 7"ID chimney makes all the difference, and as others mentioned, going too large can reduce the draft as well, although on an interior chimney it makes less difference for it to be too large. if you can put up an 8/8 masonry chimney that is tall and runs on the interior of your house; make sure that wherever it exits, it's high above the house, remember the 10/2 rule is just a MINIMUM, not a reccomendation for good draft.

 
Josh H
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Post by Josh H » Wed. Oct. 29, 2008 7:58 pm

Dallas wrote:Is your house too tight? Open a window and see what happens.
Thanks Dallas
My 1850 farmhouse is definatly not too tight, have tried opening the front door etc. I appreciate your reply, I am certainly not ready to rule out operator error.
Berlin wrote:there's something about the smell of bituminous coal and wood burning together that's nauseating, whereas one or the other burned separtely smells completely different and imho, not bad at all. as far as the chimney issue, I can almost say with a certainty that the 6" chimney is your problem. it has been my experience that an 8" or even a 7"ID chimney makes all the difference, and as others mentioned, going too large can reduce the draft as well, although on an interior chimney it makes less difference for it to be too large. if you can put up an 8/8 masonry chimney that is tall and runs on the interior of your house; make sure that wherever it exits, it's high above the house, remember the 10/2 rule is just a MINIMUM, not a reccomendation for good draft.
Thanks Belin,
I was hoping you would chime in, I think we burn the same coal and I still intend on building your stove for the shop.I think I will go with the 8X8 . I would like to go pretty high but have concerns with how high it can be off the roof unsupported. My current setup is up pretty high, but I have been noticing alot of old chimneys with a good lean and that obviously concerns me.
Thanks, Josh

 
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Berlin
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Post by Berlin » Wed. Oct. 29, 2008 9:27 pm

hi josh,

yea, a lot of older chimneys used a higher lime mortar that would expand when saturated with condensed nat gas exhaust. use a good (quickrete type S mason's mix for example) mortar, seal the tiles properly, build the chimney plumb, and you should be fine making it quite high above the roofline.

 
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Post by LsFarm » Thu. Oct. 30, 2008 8:34 pm

About the smoke spillage... open your ashpan door, as was mentioned above,, get the fire 'reved up' then close the ashpan door, and SLOWLY open the top or loading door,, let the air velocity increase in the chimney,, this can take a moment or two.. you can have a very strong draft, and no velocity,, or a much lower draft but very high velocity.. to pull the smoke/stink up the chimney requires air velocity pulling through the doorway..

I always had this problem with my Big Bertha boiler.. it has a multiple-pass smoke route, and needed a minute or two to develope enough velocity to pull the smoke away from the doorway..

It always amazed me how much smoke a shovel full of high volitile bituminous coal can make.. a quart of coal will in 2 minutes make enough thick, opaque smoke to fill a 2 car garage... and man does it stink... makes the skunks run away ! :lol: At least the coal I was burning did!!

Greg L.

 
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Post by coaledsweat » Thu. Oct. 30, 2008 9:07 pm

rockwood wrote:I personally would not install a chimney outside the pressure envelope of a house because of the potential draft problems it could have. I know by experience that a properly installed inside chimney will always make draft and an exterior one may or may not.
In the old days when all the wood was owned by the King, no mason would build an exterior chimney as the King would have his head for wasting his wood because of it. The way chimneys were built never changed because interior chimneys will not only draft better, they give up their heat to the interior of the home, not the outside. This practice remained until the advent of forced draft oil and gas appliances as they supply their own draft and do not rely on the chimney.

 
Josh H
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Post by Josh H » Fri. Nov. 07, 2008 7:38 pm

LsFarm wrote:About the smoke spillage... open your ashpan door, as was mentioned above,, get the fire 'reved up' then close the ashpan door, and SLOWLY open the top or loading door,, let the air velocity increase in the chimney,, this can take a moment or two.. you can have a very strong draft, and no velocity,, or a much lower draft but very high velocity.. to pull the smoke/stink up the chimney requires air velocity pulling through the doorway..

Greg L.
I tried this and it helps a little. It does however help me visualize the problem.

Thanks, Josh

 
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Post by Dann757 » Sat. Nov. 08, 2008 4:53 am

I'm getting ready to install my stove. It always had smoke spillage when I used wood. I heard that if the area of the opened door is much greater than the flue, there is a tendency for smoke to spill. That was when I was using 5" flue pipe, though.I have an 8x8 interior chimney coming up out of a flat roof.
I put an extra 2' flue liner on top of the chimney last year, it had little effect so I took it back off. Chimney comes up about 6' out of the roof. (Easy to inspect and clean!)
My stove has an oval outlet, I took the perimeter and calculated, it translates to an 8" diameter. So I got 8" black single wall stove pipe and intend to work it into the chimney. I'm going to have to do a lot of careful chipping to enlarge the old 6" hole. I have refractory cement to make a safe, tight connection.
Any advice on this plan much appreciated.

 
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rockwood
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Post by rockwood » Sat. Nov. 08, 2008 9:43 pm

I'm confused. Are you reinstalling your stove or was a different stove connected to the 8x8 chimney last year? Why was 5" pipe used?


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