Shenandoah Wood Coal Stove Poor Output

 
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Cap
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Post by Cap » Sat. Dec. 12, 2009 10:42 am

Brian,
How many lbs. of coal will the firebox hold? My guess would be you need at least 50-75 lbs. but any less could be a reson for poor heat output especially without a fan motor.

Is the unit tight otherwise? Is the flue pipe sucking air at any connections? Try using a candle or a long match stick and see where you could be sucking air other than the damper. Any air being pulled from a areas above the firebox ( not thru the coal fire ) will effect your ability to draft which sounds like your problem above 30F.


 
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oliver power
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Post by oliver power » Sat. Dec. 12, 2009 10:53 am

Here is some theory for you to ponder. The gasses from wood heat are a lot hotter than gasses from coal heat. The hotter the gasses, the better the draw (chimney draft). With a wood fire, you can close down the manual damper, keeping heat in the stove, and still have a decent draw on the chimney. Closing the manual damper on a coal fire, restricts air flow, as well as chimney draft. A coal fire thrives on air flow. You open the manual damper, and your heat from the coal stove goes up the chimney. You need to let the air flow, without sucking the stove heat up the chimney. So, along with other good advice, take out the manual damper(or leave it wide open), and add a barometric damper higher in the pipe. Doing this, you will not be restricting air flow through the coal fire. Yet, instead of drawing high BTU stove heat out of the stove in order to get decent chimney draft, you will be drawing room temperature air for draft. I'd start there. Because of you saying the chimney has poor draw, you may want to consider putting a hat over the chimney openning. Down drafts, as well as low atmospheric preasure can also weaken chimney draft. One more thing; A wood fire doesn't depend on draft from below the grates. A coal fire does. An ash build up on the grates will give you problems. Keep the grates open.
Last edited by oliver power on Sat. Dec. 12, 2009 11:01 am, edited 1 time in total.

 
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Post by brian315 » Sat. Dec. 12, 2009 10:57 am

I think you may be right Cap, I have tried to build the coal bed slowly trying not to smother it and cant seem to get the volume I need to get the output I want and I believe the draft is why im going to work on it today and see if I can eliminate as many draft robbing issues as possible, thank you all for the help

 
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oliver power
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Post by oliver power » Sat. Dec. 12, 2009 11:41 am

brian315 wrote:I think you may be right Cap, I have tried to build the coal bed slowly trying not to smother it and cant seem to get the volume I need to get the output I want and I believe the draft is why im going to work on it today and see if I can eliminate as many draft robbing issues as possible, thank you all for the help
Make sure your cap is simple, like a graduates hat. A simple flat hat. When it comes to coal fires, & bad drafts, some of the fancy caps out there are as bad as having no cap. You'll want about a 6 inch space between the flue, and the top of cap. I suggest thick steal, or solid copper for material. Acids in fly ash will eat up caps that are cheap stainless or copper coated.

 
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Post by brian315 » Sat. Dec. 12, 2009 11:47 am

I was thinking about the cap, i'm assuming that the cap actually holds some heat in the chimney and thereby improves draft overall while letting gas escape, is this the theory? I'm going to head out and get some stick on thermometers and some kind of high temp sealant for flue to stove connection, and suggestions?

 
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oliver power
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Post by oliver power » Sat. Dec. 12, 2009 11:56 am

brian315 wrote:I was thinking about the cap, i'm assuming that the cap actually holds some heat in the chimney and thereby improves draft overall while letting gas escape, is this the theory? I'm going to head out and get some stick on thermometers and some kind of high temp sealant for flue to stove connection, and suggestions?
No, you don't want to hold heat in the chimney. That's why you don't want a fancy cap. You want everything in the chimney to go up and out. This will give you a stronger draft. A warmer chimney is also good. That's why an interior chimney is always better than an exterior chimney. Sometimes a lot more work to add in an existing structure. That's why many people install exterior chimneys. It's not because it's better, but a lot less work.

 
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Post by packard bill » Sat. Dec. 12, 2009 2:29 pm

Your chimney is probably pulling way to much draft, thereby sucking an excess of fresh combustion air into the stove and your heat is going up the chimney. When you build your fire you get it going good and hot, right? Well, the hotter the fire the hotter the combustion gasses going up the chimney, warming the chimney, thereby creating even more draft.

You NEED a barometric damper. I'm guessing your chimney is probably 8" x 8", and at your height, it is too big for the stove. Install a barometric and take your stack temp before the baro and take the temp between the baro and the chimney.

Just for giggles take a stack temp. reading when you get your magnetic thermometer and post it here. Then install the baro. and take your readings.

If your stove doesn't have any air leaks or cracks, I bet you'll see a difference.

Good luck.


 
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Post by packard bill » Sat. Dec. 12, 2009 2:37 pm

By the way, I forgot, if you plan on burning wood, forget about the barometric. Burn either coal and set up for it, or burn wood and leave it the way it is.

 
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Post by brian315 » Sat. Dec. 12, 2009 2:54 pm

I couldnt find thermometers anywhere, ill make some calls, where exactly should I take reading? my flue is straight up from stove top approx 20" to a elbow then about 30" to chimney mortared in. The manual damper is about 18 inches up from stove in vertical pipe section.

 
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Post by brian315 » Sat. Dec. 12, 2009 7:52 pm

Question? best placement of fitting for manometer? best placement for baro damper?

 
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Cap
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Post by Cap » Sat. Dec. 12, 2009 9:49 pm

Brian, if you are having problems drafting, a baro will make matters worse. Baro's reduce draft to prevent your bed of coal from burning to quickly thus not making the heat everybody else is telling you is escaping up the flue. Get your system tight especially above the bed of coal.

A manometer should be just above the outlet stove piping. A manometer will help more until you straighten out your flue piping issues..

 
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Post by brian315 » Sat. Dec. 12, 2009 10:04 pm

that was my thinking, lets see what the thing is pulling in wc. before I do anything, that cart in front of the horse never works lol, I have access to very accurate hvac test kit and have some experience in building gas train airhandlers from scratch and in pneumatic and electrical controls, i'm no boiler mechanic by any means and know next to nothing and prove it on a constant basis lol

 
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Post by oliver power » Sun. Dec. 13, 2009 10:13 am

Cap wrote:Brian, if you are having problems drafting, a baro will make matters worse. Baro's reduce draft to prevent your bed of coal from burning to quickly thus not making the heat everybody else is telling you is escaping up the flue. Get your system tight especially above the bed of coal.

A manometer should be just above the outlet stove piping. A manometer will help more until you straighten out your flue piping issues..
Baro's don't reduce chimney draft. They reduce excess drawing of the stove air, by pulling in room air. They draw enough on the stove to exit the fumes, leaving the heat in the stove. If the baro damper is closed, it's like not having one. I don't know about other's, but I don't know how the Shenandoah is designed on the inside. I'm assuming it is a combo stove, and may not have a very good way of extracting heat from gasses, before entering the exaust pipe. I would always recommend a baro damper in a combo stove when burning coal. A temp gauge on the stove pipe would tell you whether or not the coal is burning as it should be. With the manual damper fully open, your pipe temp would probably be around 150* - 200*, and the stove should be cranking out heat. If the stove is not cranking out heat at those pipe temps(or higher), you need to install a baro damper. We are all assumeing your chimney draft is bad, as was said.

 
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Post by brian315 » Sun. Dec. 13, 2009 10:45 am

Thank you Oliver, and you right it is just a barrel stove with a shaker grate and a somewhat sealed underfire ashpan compartment and a bimetal spring controlled inlet. As you state a baro cant hurt if it's closed and seals good, even if the draft is weak.

 
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Post by brian315 » Sun. Dec. 13, 2009 7:58 pm

Ok I have a stack temp reading with and average type of coal bed my stove will produce under the outside air temps today, about 30 degrees calm and high humidity, with small blue flames and about 8" red coal I'm running around 200 stack temp


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