Help troubleshooting weird creosote problem?

[firekindler]

I've been living with woodstoves for 35 years and have never seen anything like this. For the past four years I've been living with a Fisher Papa Bear. It's a great stove and I like it. It's got brick lining and five fin draft control knobs, so I think it's UL listed (post 1980?). But when I shut it down to smolder overnight, the flue gets pressurized and forces creosote out of anyplace it can escape. Here's the situation:
The stove has been modified in three ways. The rear vent was covered and a top vent installed. A baffle was installed. And at one point it had a hot water manifold in the firebox so there are two small outlets for waterlines in the rear which are now capped. The flue is 6", same as stock, and rises straight up with no bends or elbows. There is 12' of single wall black pipe up to the ceiling (cathedral ceiling), a slip connector, and probably a 3' section of metalbestos chimney, which exits near the roof peak so it's top is higher than any part of the roof. The draw is nothing short of voracious. Open the damper and it sounds like a jet taking off. My wood is well seasoned (stacked on pallets in the California sun) and overwhelmingly hardwood (tanoak, madrone, California black oak, Oregon white oak, manzanita, and occasionally a little California bay laurel or coffee berry). Knowing the bay laurel tends to create creosote, I almost never use it when the stove is shut down overnight. I use Douglas fir limbwood, but only when I have the damper wide open to speed up taking out the chill in the room after a period of shutdown. At least once a day, and always in the morning after the night's long shutdown, I open the damper fully and crank the stove at full bore for at least 40 minutes to help burn off residue in the pipe. The flue is constructed with the crimped ends down, so creosote should just drip back into the stove.
But instead, it began leaking out the (properly sized) hole for the damper rod, and the seams of the snap locked black pipe. It rotted the pipe so I replaced the entire 12' with heavier gauge single wall black pipe, with welded seams. I got rid of the damper, so no holes. After only two or three months of use, now the creosote is forcing it's way through the welded seams and dripping down the outside of the pipe. I can see no gaps in the seams visually, after the creosote burns off. That sounds like some serious pressure. Why does the creosote not just drip down the inside of the pipe into the firebox? I've spoken with two different technical help engineers at Selkirk (metalbestos' manufacturer) and they are both (pardon the expression) baffled. The only remotely plausible explanation was that maybe the house is tight enough to starve the shut down stove from enough air to avoid the pressurization. Except that would be laughable; this is far from a tight house, including many single pane windows and some with discernible drafts. Yesterday one of them referred me to this fine website, where I spent some time researching threads.
What sort of voodoo may be tormenting me? I understand that using double wall black pipe is supposed to help with creosote issues, but I would prefer to keep it single wall if possible for more heat radiance into the room.

 

[bholler]

I've been living with woodstoves for 35 years and have never seen anything like this. For the past four years I've been living with a Fisher Papa Bear. It's a great stove and I like it. It's got brick lining and five fin draft control knobs, so I think it's UL listed (post 1980?). But when I shut it down to smolder overnight, the flue gets pressurized and forces creosote out of anyplace it can escape. Here's the situation:
The stove has been modified in three ways. The rear vent was covered and a top vent installed. A baffle was installed. And at one point it had a hot water manifold in the firebox so there are two small outlets for waterlines in the rear which are now capped. The flue is 6", same as stock, and rises straight up with no bends or elbows. There is 12' of single wall black pipe up to the ceiling (cathedral ceiling), a slip connector, and probably a 3' section of metalbestos chimney, which exits near the roof peak so it's top is higher than any part of the roof. The draw is nothing short of voracious. Open the damper and it sounds like a jet taking off. My wood is well seasoned (stacked on pallets in the California sun) and overwhelmingly hardwood (tanoak, madrone, California black oak, Oregon white oak, manzanita, and occasionally a little California bay laurel or coffee berry). Knowing the bay laurel tends to create creosote, I almost never use it when the stove is shut down overnight. I use Douglas fir limbwood, but only when I have the damper wide open to speed up taking out the chill in the room after a period of shutdown. At least once a day, and always in the morning after the night's long shutdown, I open the damper fully and crank the stove at full bore for at least 40 minutes to help burn off residue in the pipe. The flue is constructed with the crimped ends down, so creosote should just drip back into the stove.
But instead, it began leaking out the (properly sized) hole for the damper rod, and the seams of the snap locked black pipe. It rotted the pipe so I replaced the entire 12' with heavier gauge single wall black pipe, with welded seams. I got rid of the damper, so no holes. After only two or three months of use, now the creosote is forcing it's way through the welded seams and dripping down the outside of the pipe. I can see no gaps in the seams visually, after the creosote burns off. That sounds like some serious pressure. Why does the creosote not just drip down the inside of the pipe into the firebox? I've spoken with two different technical help engineers at Selkirk (metalbestos' manufacturer) and they are both (pardon the expression) baffled. The only remotely plausible explanation was that maybe the house is tight enough to starve the shut down stove from enough air to avoid the pressurization. Except that would be laughable; this is far from a tight house, including many single pane windows and some with discernible drafts. Yesterday one of them referred me to this fine website, where I spent some time researching threads.
What sort of voodoo may be tormenting me? I understand that using double wall black pipe is supposed to help with creosote issues, but I would prefer to keep it single wall if possible for more heat radiance into the room.

What flue temps are you running at?

 

[firekindler]

What flue temps are you running at?

Right now it's been shut down for about three hours, and the thermometer (about six inches above the outlet) reads 60-65 degrees. That makes me wonder if it's accurate; seems too low. The pipe is warm to the touch and the room temperature is 69.3. When I open the dampers and blast the stove it usually runs at 500-700.

 

[Todd67]

Welcome to the forum!

When you shut the stove down at night, are you closing the draft caps all the way?

 

[firekindler]

Thanks for the welcome, Minister. Yes, I close them all the way. Normally I get them as tight as I can get them by hand, and often by morning they've loosened just a wee smidgin'. But last night I experimented by snugging them, but not as tight as possible. I started thinking that maybe as the pipe cools the damped down fire draws air from the top of the chimney to feed itself. But to my mind, that still doesn't explain why the creosote doesn't just take the path of least resistance and drain into the stove instead of forcing itself out of tight places.

 

[bholler]

Right now it's been shut down for about three hours, and the thermometer (about six inches above the outlet) reads 60-65 degrees. That makes me wonder if it's accurate; seems too low. The pipe is warm to the touch and the room temperature is 69.3. When I open the dampers and blast the stove it usually runs at 500-700.

That doesn't answer what the pipe temp is when you are running normally. How is it running overnight when you shut it all the way down?

 

[Todd67]

Closing them all the way is not allowing your stove and chimney to burn cleanly and efficiently. Do you have one of these stove pipe thermometers?



I have my draft caps open very little, 1/4 turn and my pipe temp is 120*.

 

[Todd67]

I heat my drafty old 2-story house in northern NY with a Mama Bear, been using it for 8 years as my only heat source.

When I load the stove, here is the process I follow every time.

Open the draft caps all the way, then open the door and load the stove. If you have coals in your stove, pull them forward and level out the bed of coals before loading the stove. Load the stove and close the door. Let the fire get going real good, keeping an eye on your stove pipe thermometer. Once that thermometer reaches 500 degrees, close your draft caps, then open them 1/4 turn. On real cold nights I open them 1/2 turn. I believe you are getting creosote buildup in your chimney because the chimney gases (smoke) is cooling too much before it leaves your chimney. My chimney is 21ft tall outside and I never have a creosote issue. By getting the stove pipe up to 500* every time you load your stove, it helps burn off creosote that might be building up in your chimney, but not all of it.

 

[firekindler]

That doesn't answer what the pipe temp is when you are running normally. How is it running overnight when you shut it all the way down?

I usually blast it pretty good up to 500-700 degrees before shutting it down. It seems to cool down to 275-300 for a while thereafter (couple of hours?). Then it's pretty cool by morning. Most of the time I either have the knobs all the way open or all the way closed. This has been my habit for decades.

 

[firekindler]

Closing them all the way is not allowing your stove and chimney to burn cleanly and efficiently. Do you have one of these stove pipe thermometers?

View attachment 253409

I have my draft caps open very little, 1/4 turn and my pipe temp is 120*.

Yes, although yours is more colorful than mine. Same brand, though. Not to distract from the issue at hand, but I'm curious why you have multiple thermometers on yours?

 

[firekindler]

I heat my drafty old 2-story house in northern NY with a Mama Bear, been using it for 8 years as my only heat source.

When I load the stove, here is the process I follow every time.

Open the draft caps all the way, then open the door and load the stove. If you have coals in your stove, pull them forward and level out the bed of coals before loading the stove. Load the stove and close the door. Let the fire get going real good, keeping an eye on your stove pipe thermometer. Once that thermometer reaches 500 degrees, close your draft caps, then open them 1/4 turn. On real cold nights I open them 1/2 turn. I believe you are getting creosote buildup in your chimney because the chimney gases (smoke) is cooling too much before it leaves your chimney. My chimney is 21ft tall outside and I never have a creosote issue. By getting the stove pipe up to 500* every time you load your stove, it helps burn off creosote that might be building up in your chimney, but not all of it.

I understand the principle. Your process is similar to mine, except I usually have the knobs all the way open or all the way closed. That's been my habit for decades, and I've never had creosote problems. If all it was is creosote production, there would not be an issue. The issue is the pressurization that forces it to defy gravity and leak through the tight spots rather than drip into the stove. Is it possible the Papa Bear is so much more airtight than any other stove I've ever operated that it creates the pressurization inside the pipe?

 

[Todd67]

If the chimney gases are below 250* when they exit your chimney, you will have creosote forming in your chimney. Try the 1/4 turn open method and see if that works.

Also, I run a ceiling fan on low in my living room, turn normal direction to push air down.

 

[coaly]

First, creosote is the solid matter that builds up inside the chimney flue and pipe. It is not liquid. Creosote is unburned smoke particles that stick to the wet walls of the pipe and chimney flue.
The liquid is condensed water vapor from combustion. When smoke is present, the inner flue walls must remain above 250* f. to the top. Below this critical temperature, water vapor condenses on walls allowing smoke particles to stick. You should have little to no liquid inside the pipe. Any liquid is a sign of running too cool. It is not making it out of the chimney (as steam) due to cooling too much before the roof line. You need double wall pipe when installed with more than an 8 foot ceiling.

The only time air inlet dampers are closed fully is when testing to see if the fire goes out with them closed when testing for air tightness, or during a chimney fire to deprive the chimney of oxygen. The fire should die to a glow, no flames or go out when fully closed. Make sure your door seal is clean, it should go out with them closed. Only close them, never tighten down snug. There is no reason to tighten them, ever. The opening is how many square inches atmospheric air pressure has to push into the stove. The larger the opening, the more area the atmosphere has to push with. Once the draft cap is just cracked open, that is the minimum amount needed. They always need to be at least cracked open for a slight amount of intake air. Closing too far will drop the chimney temperature below condensing point. So 1/4 to 1/2 turn is more like a low fire, 1 turn should be medium, 1 1/2 to 2 turns is all it should take for plenty of heat once up to temp. 3 turns to start a fire should be enough to make it roar.

A damper is a chimney control. It slows the velocity of rising gasses, which decreases draft, affecting the stove by decreasing air coming into stove. You should be controlling air with intake dampers since you have very little chimney to cause draft. The excessive connector pipe inside reduces draft due to friction and cooling as it rises. The insulated chimney retains heat increasing draft. So you don't have a large "engine" to make the stove go that needs to be throttled down with a pipe damper.

Do you have plenty of coals in the morning to rake ahead to start a new fire on?

Where is your pipe thermometer located?
You need to check pipe temperature just below where it enters into chimney. (support box)The pipe surface temp will be about 1/2 the actual inside exhaust gas temp. Then allow for cooling to the top of insulated chimney to strive for 250* coming out the top. As an example, 200 on the pipe thermometer = 400* internal. This cools in a taller chimney before exiting. Your short chimney will not cool as much, so it's a guess how much cooling you have to the top without taking a temp reading a foot or so below the top with an infrared thermometer. Then you would know what you have at any given inside temp.

Trying to radiate more heat from pipe into the room is not the way to make the stove work. BTU output comes from the temperature of every square inch of radiating surface of the stove. A baffle inside stove directs more heat to the stove top and forward away from the exhaust vent. What rises out of the stove is waste, needed to keep the chimney above the 250* operating temp. (when smoke is present) Double wall pipe keeps the rising gasses hotter all the way up, so the chimney is warmer inside with less fuel waste. The chimney makes the stove go, so it needs heat to make oxygen PUSH into the stove. The connector pipe takes away from the chimney. You're not feeding the flue enough heat to make the stove go by cooling the exhaust gasses before the chimney. Less heat going out = more heat inside to heat the area you're heating. Example; set a hot cookie sheet on a stove top. It will burn your hand, feel very hot, and cool quickly, not adding much heat to the room. Heat a thick piece of iron that cools slowly, it radiates heat into the room.

5 fin intake dampers does not mean it is UL listed. If it has flat top doors, it is not Listed. A Listed stove will also have a UL tag on the back. A picture with door shut will verify what you have.

What was the rear vent covered with? is it sealed airtight? Any leak will allow indoor air to keep the fire burning with intake dampers closed as well as letting cooler indoor air leak into the chimney, cooling it even farther.

My guess is once you have water dripping down the inside of connector pipe, colder outside air drops down the chimney allowing moisture to leak through seams. Open the intake dampers in the morning, or the door and see if you feel cold air coming into the house from chimney. If so, you have a depressurized house using the chimney as an air intake from something such as mechanical fan, furnace, gas water heater, dryer, exhaust fans, radon blower?? Is there another chimney in the home?

 

[firekindler]

If the chimney gases are below 250* when they exit your chimney, you will have creosote forming in your chimney. Try the 1/4 turn open method and see if that works.

Also, I run a ceiling fan on low in my living room, turn normal direction to push air down.

View attachment 253410

I have two ceiling fans which I run on high forcing the air down while I'm awake, and I shut them off when I go to bed. Do you recommend running them on low all night? And how would that affect pressurization inside the pipe?

 

[Todd67]

I run mine on low all day and all night. Through trial and error I have found that running it on low helps feed air through the draft caps (opened 1/4 turn), which helps the stove burn less wood, burn cleaner, and put off more heat. We've tried running the fan on low in reverse mode, and not running it at all, and there's no comparison to the results we get by running it on low 24/7.

The affect inside the pipe is that the draft moves continuously through & up the chimney as it is supposed to, and helps keep the gases/smoke above 250* to prevent creosote formation.

 

[Todd67]

Coaly explains the creosote thing better than anyone!

 

[bholler]

Coaly explains the creosote thing better than anyone!

Yes he does very good but creosote is not always a solid at all. It melts at a fairly low temperature. But that really doesn't matter much. He is dead on otherwise

 

[coaly]

I have two ceiling fans which I run on high forcing the air down while I'm awake, and I shut them off when I go to bed. Do you recommend running them on low all night? And how would that affect pressurization inside the pipe?

You want to run the fans pulling up, not down in the winter.
#1, The natural flow is to rise up off the stove, it is much easier to move air in the natural direction of flow, not against it.
#2, Moving hot air downward into cooler air is trying to move lighter more buoyant air into colder denser air. Cold dense air pushes lighter air out of the way moving it. Hot air does not move cold air as easily.
#3, Pushing air downward in the center of rooms where people are allow them to feel drafts. Pulling up hits the ceiling and moves down the walls, at the room edges where people are not usually there to feel a draft cooling them.

Pushing air down in the summer moves air across people that are normally in the center of the room, taking advantage of evaporation on their body to cool them. You don't want to do that in winter.

You don't want any moving air to cool the single wall pipe. You are making it a condenser inside.
Pressure inside pipe is lower than outside when stove is fired. Cooling it increases this lower than atmospheric pressure. Increased pressure in pipe = less air pushing into stove, causing lower fire.

I'm not sure what you mean by pressurization inside the pipe and chimney. "Pressurized" is above atmospheric pressure. In an engine, this would be a turbocharger or supercharger pressurizing the intake air. A vehicle without pressurization is a "normally aspirated" engine. That's what your stove is. Aspirated by atmospheric pressure.

You can only pressurize something that is sealed. The chimney is open top and bottom. (the most resistance to flow is the air intake on the stove, which is open during use) Temperature and pressure are related in a sealed system. As you heat it up, it increases in pressure. Cooling it decreases pressure causing a vacuum. You don't have a sealed pressurized container. The stove when burning, creates gasses hotter and lighter than outside air to rise up the chimney. This makes a lower pressure area in the chimney, pipe and stove. The lowest pressure is measured at the flue collar of the stove. Measured as draft. Atmospheric air pressure which constantly changes, (different with altitude and weather factors) then PUSHES air with oxygen into the intake opening, feeding the fire oxygen. Replacement air comes from every crack or opening in the structure it can, or through an air intake close to the stove for this purpose. Running a clothes dryer or any exhaust fans or vented appliances (vented boiler, furnace, water heater- especially power vented appliances) decreases the pressure in the building which decreases the "PUSH" into the stove. In extreme cases the chimney becomes the intake for the home. With or without the fire going. This is atmospheric pressure pushing into the home to fill the void created by mechanical blowers. It is not pressurizing theme, it is balancing the indoor and outdoor pressure.

These pressures are very very minute. Far less than your breath. As an example, propane operating pressure is 1/2 psi which is 10 - 11 inches water column. Natural gas operates at 1/4 psi or 5 inches of water column. (same theory as measuring blood pressure with mercury) Water Column gauge is a U shaped piece of tubing or hose with water in it. The water finds a level on each side holding it in a U shape with both ends open to the atmosphere. Pressure pushing down one side raises the other side up the same amount. Adding these two measurements together gives you water column pressure. 1/2 inch down one side, 1/2 up the other = 1 inch W.C. These pressure differentials in a chimney are far less than 1 inch water column. Like .03 or .04 inch being a draft to make a stove work. We're no longer measuring with a ruler here. That minute pressure does not move water on the surface of a pipe 6 inches in diameter.

This is why I ask if there are other vented appliances in the building decreasing building pressure.

 

[Todd67]

That all makes perfect sense coaly, and that's why I tried that method first (pulling air up). But I can't explain why pushing the air down works better in my house. The entire house feels warmer, including the upstairs. I'm not trying to debate anything here because my method defies what we know to be true. Maybe it's my floorplan, or the type of fan I have, I don't know.

I have a ceiling fan at the top of my stairs that runs on low in reverse, pulling warm air up.

I agree that firekindler should try running the fans in reverse mode first.

 

[Todd67]

Come to think of it, I have a 16" tall beam in my house that runs east to west along the entire length of my first floor ceiling. It seems to trap a lot of warm air along the south half of my house, making the rooms on the north side of the house feel colder. We've confirmed this with a digital thermometer in each room. Running the ceiling fan in normal mode seems to reduce the temperature difference in the colder rooms.

My house is also very drafty around the windows, which doesn't help. This is the beam along the ceiling.

 

[firekindler]

That doesn't answer what the pipe temp is when you are running normally. How is it running overnight when you shut it all the way down?

Ok - back at it today. Firstly, I erred in reporting the 60-65 degree temperature. I mistakenly read the Centigrade scale instead, so it was really 140=150.

 

[coaly]

Come to think of it, I have a 16" tall beam in my house that runs east to west along the entire length of my first floor ceiling. It seems to trap a lot of warm air along the south half of my house, making the rooms on the north side of the house feel colder. We've confirmed this with a digital thermometer in each room. Running the ceiling fan in normal mode seems to reduce the temperature difference in the colder rooms.

My house is also very drafty around the windows, which doesn't help. This is the beam along the ceiling.

View attachment 253480

Yep, to visualize how heat flows, picture the house turned upside down. The stove or heat source is like a faucet supplying water to fill the house. It would fill across ceiling first, and have to fill up until it spills over the beam. That's what the heat is doing like a waterfall over the beam. Keeping the warm air from rising is pushing it sideways into the other rooms. The smaller the room the fan is in, the more efficient it's going to keep the heat from rising into that room. If you had one large room, it would be more efficient rising in the center, pushing down the walls.
My open floor plan uses one small doorway type fan in a wall near the ceiling to even out a 10* difference from stove area to the rest of the house. I'm on one level, built to heat with a central stove in the center of kitchen.

 

[firekindler]

First, creosote is the solid matter that builds up inside the chimney flue and pipe. It is not liquid. Creosote is unburned smoke particles that stick to the wet walls of the pipe and chimney flue.
The liquid is condensed water vapor from combustion. When smoke is present, the inner flue walls must remain above 250* f. to the top. Below this critical temperature, water vapor condenses on walls allowing smoke particles to stick. You should have little to no liquid inside the pipe. Any liquid is a sign of running too cool. It is not making it out of the chimney (as steam) due to cooling too much before the roof line. You need double wall pipe when installed with more than an 8 foot ceiling.

The only time air inlet dampers are closed fully is when testing to see if the fire goes out with them closed when testing for air tightness, or during a chimney fire to deprive the chimney of oxygen. The fire should die to a glow, no flames or go out when fully closed. Make sure your door seal is clean, it should go out with them closed. Only close them, never tighten down snug. There is no reason to tighten them, ever. The opening is how many square inches atmospheric air pressure has to push into the stove. The larger the opening, the more area the atmosphere has to push with. Once the draft cap is just cracked open, that is the minimum amount needed. They always need to be at least cracked open for a slight amount of intake air. Closing too far will drop the chimney temperature below condensing point. So 1/4 to 1/2 turn is more like a low fire, 1 turn should be medium, 1 1/2 to 2 turns is all it should take for plenty of heat once up to temp. 3 turns to start a fire should be enough to make it roar.

A damper is a chimney control. It slows the velocity of rising gasses, which decreases draft, affecting the stove by decreasing air coming into stove. You should be controlling air with intake dampers since you have very little chimney to cause draft. The excessive connector pipe inside reduces draft due to friction and cooling as it rises. The insulated chimney retains heat increasing draft. So you don't have a large "engine" to make the stove go that needs to be throttled down with a pipe damper.

Do you have plenty of coals in the morning to rake ahead to start a new fire on?

Where is your pipe thermometer located?
You need to check pipe temperature just below where it enters into chimney. (support box)The pipe surface temp will be about 1/2 the actual inside exhaust gas temp. Then allow for cooling to the top of insulated chimney to strive for 250* coming out the top. As an example, 200 on the pipe thermometer = 400* internal. This cools in a taller chimney before exiting. Your short chimney will not cool as much, so it's a guess how much cooling you have to the top without taking a temp reading a foot or so below the top with an infrared thermometer. Then you would know what you have at any given inside temp.

Trying to radiate more heat from pipe into the room is not the way to make the stove work. BTU output comes from the temperature of every square inch of radiating surface of the stove. A baffle inside stove directs more heat to the stove top and forward away from the exhaust vent. What rises out of the stove is waste, needed to keep the chimney above the 250* operating temp. (when smoke is present) Double wall pipe keeps the rising gasses hotter all the way up, so the chimney is warmer inside with less fuel waste. The chimney makes the stove go, so it needs heat to make oxygen PUSH into the stove. The connector pipe takes away from the chimney. You're not feeding the flue enough heat to make the stove go by cooling the exhaust gasses before the chimney. Less heat going out = more heat inside to heat the area you're heating. Example; set a hot cookie sheet on a stove top. It will burn your hand, feel very hot, and cool quickly, not adding much heat to the room. Heat a thick piece of iron that cools slowly, it radiates heat into the room.

5 fin intake dampers does not mean it is UL listed. If it has flat top doors, it is not Listed. A Listed stove will also have a UL tag on the back. A picture with door shut will verify what you have.

What was the rear vent covered with? is it sealed airtight? Any leak will allow indoor air to keep the fire burning with intake dampers closed as well as letting cooler indoor air leak into the chimney, cooling it even farther.

My guess is once you have water dripping down the inside of connector pipe, colder outside air drops down the chimney allowing moisture to leak through seams. Open the intake dampers in the morning, or the door and see if you feel cold air coming into the house from chimney. If so, you have a depressurized house using the chimney as an air intake from something such as mechanical fan, furnace, gas water heater, dryer, exhaust fans, radon blower?? Is there another chimney in the home?

Thank you coaly, that is quite an education. Firstly, I was mistaken in my use of "damper" in the first few paragraphs of my initial post. I meant "draft control knobs" in that context ("open the draft control knobs and it sounds like a jet taking off"). As I stated farther down, I eliminated the pipe damper in the latest configuration. And yes, it has flat top doors, so therefore unlisted.

Commonly, let's say I get home from work around 6. I'll feed the stove, run it at full blast for 30-60 minutes depending on the inside and outside air temperatures. That will build a good bed of coals and get the inside temperature up to comfortable. Then unless it's a colder night, I'll load a 6-12" diameter unsplit piece (but still well seasoned) or maybe two somewhat smaller pieces. I'll wait until those are burning well, the pipe temperature is up to 500 or so, then close the intake knobs as described earlier. Most of the time, up to 12-14 hours later I'll still have decent coals, certainly enough to revive the fire without needing paper/cardboard, and often without needing any wood kindling. Once in a while it will go out completely. If I'm up early for work (let's say 10 hours later), there will usually be a lot of coals and a good chunk of the all-night piece left. Been doing that practice pretty much since day one with good results with a number of different stoves. Had a similar situation once with a newer, double door Fisher, similar amount of pipe, but no ceiling fan previously. But never had any creosote issues before this place. And with a similar loading example, I have found that leaving the intake draft control knobs just barely cracked open makes it so the wood and coals won't last anywhere close to that long.

My pipe thermometer is about six inches above the outlet. Don't have an infrared thermometer, but that's a good suggestion. May have to remedy that lack.

The rear vent is covered with a thin sheet of steel, welded on. I'm assuming it's airtight. If not, I would have smoke leaking into the room when shut down, right?

How does colder outside air dropping down the chimney allow moisture to leak through the seams? Why doesn't it just drain down into the stove? Some fairly powerful force is pushing it to defy gravity. I've never noticed cold air coming out of the stove upon opening the door, but I'll pay specific attention next time. Aside from the ceiling fans, which I almost always turn off at night, none of the appliances you list exist inside the home. And there is no other chimney.

Thanks again; on to your next post.

 

[bholler]

Thank you coaly, that is quite an education. Firstly, I was mistaken in my use of "damper" in the first few paragraphs of my initial post. I meant "draft control knobs" in that context ("open the draft control knobs and it sounds like a jet taking off"). As I stated farther down, I eliminated the pipe damper in the latest configuration. And yes, it has flat top doors, so therefore unlisted.

Commonly, let's say I get home from work around 6. I'll feed the stove, run it at full blast for 30-60 minutes depending on the inside and outside air temperatures. That will build a good bed of coals and get the inside temperature up to comfortable. Then unless it's a colder night, I'll load a 6-12" diameter unsplit piece (but still well seasoned) or maybe two somewhat smaller pieces. I'll wait until those are burning well, the pipe temperature is up to 500 or so, then close the intake knobs as described earlier. Most of the time, up to 12-14 hours later I'll still have decent coals, certainly enough to revive the fire without needing paper/cardboard, and often without needing any wood kindling. Once in a while it will go out completely. If I'm up early for work (let's say 10 hours later), there will usually be a lot of coals and a good chunk of the all-night piece left. Been doing that practice pretty much since day one with good results with a number of different stoves. Had a similar situation once with a newer, double door Fisher, similar amount of pipe, but no ceiling fan previously. But never had any creosote issues before this place. And with a similar loading example, I have found that leaving the intake draft control knobs just barely cracked open makes it so the wood and coals won't last anywhere close to that long.

My pipe thermometer is about six inches above the outlet. Don't have an infrared thermometer, but that's a good suggestion. May have to remedy that lack.

The rear vent is covered with a thin sheet of steel, welded on. I'm assuming it's airtight. If not, I would have smoke leaking into the room when shut down, right?

How does colder outside air dropping down the chimney allow moisture to leak through the seams? Why doesn't it just drain down into the stove? Some fairly powerful force is pushing it to defy gravity. I've never noticed cold air coming out of the stove upon opening the door, but I'll pay specific attention next time. Aside from the ceiling fans, which I almost always turn off at night, none of the appliances you list exist inside the home. And there is no other chimney.

Thanks again; on to your next post.

What moisture content is the inside of that unsplit price at? My guess is it is nowhere near as dry as it should be and when you shut your draft caps down that far you cause massive creosote problems.

 

[firekindler]

You want to run the fans pulling up, not down in the winter.
#1, The natural flow is to rise up off the stove, it is much easier to move air in the natural direction of flow, not against it.
#2, Moving hot air downward into cooler air is trying to move lighter more buoyant air into colder denser air. Cold dense air pushes lighter air out of the way moving it. Hot air does not move cold air as easily.
#3, Pushing air downward in the center of rooms where people are allow them to feel drafts. Pulling up hits the ceiling and moves down the walls, at the room edges where people are not usually there to feel a draft cooling them.

Pushing air down in the summer moves air across people that are normally in the center of the room, taking advantage of evaporation on their body to cool them. You don't want to do that in winter.

You don't want any moving air to cool the single wall pipe. You are making it a condenser inside.
Pressure inside pipe is lower than outside when stove is fired. Cooling it increases this lower than atmospheric pressure. Increased pressure in pipe = less air pushing into stove, causing lower fire.

I'm not sure what you mean by pressurization inside the pipe and chimney. "Pressurized" is above atmospheric pressure. In an engine, this would be a turbocharger or supercharger pressurizing the intake air. A vehicle without pressurization is a "normally aspirated" engine. That's what your stove is. Aspirated by atmospheric pressure.

You can only pressurize something that is sealed. The chimney is open top and bottom. (the most resistance to flow is the air intake on the stove, which is open during use) Temperature and pressure are related in a sealed system. As you heat it up, it increases in pressure. Cooling it decreases pressure causing a vacuum. You don't have a sealed pressurized container. The stove when burning, creates gasses hotter and lighter than outside air to rise up the chimney. This makes a lower pressure area in the chimney, pipe and stove. The lowest pressure is measured at the flue collar of the stove. Measured as draft. Atmospheric air pressure which constantly changes, (different with altitude and weather factors) then PUSHES air with oxygen into the intake opening, feeding the fire oxygen. Replacement air comes from every crack or opening in the structure it can, or through an air intake close to the stove for this purpose. Running a clothes dryer or any exhaust fans or vented appliances (vented boiler, furnace, water heater- especially power vented appliances) decreases the pressure in the building which decreases the "PUSH" into the stove. In extreme cases the chimney becomes the intake for the home. With or without the fire going. This is atmospheric pressure pushing into the home to fill the void created by mechanical blowers. It is not pressurizing theme, it is balancing the indoor and outdoor pressure.

These pressures are very very minute. Far less than your breath. As an example, propane operating pressure is 1/2 psi which is 10 - 11 inches water column. Natural gas operates at 1/4 psi or 5 inches of water column. (same theory as measuring blood pressure with mercury) Water Column gauge is a U shaped piece of tubing or hose with water in it. The water finds a level on each side holding it in a U shape with both ends open to the atmosphere. Pressure pushing down one side raises the other side up the same amount. Adding these two measurements together gives you water column pressure. 1/2 inch down one side, 1/2 up the other = 1 inch W.C. These pressure differentials in a chimney are far less than 1 inch water column. Like .03 or .04 inch being a draft to make a stove work. We're no longer measuring with a ruler here. That minute pressure does not move water on the surface of a pipe 6 inches in diameter.

This is why I ask if there are other vented appliances in the building decreasing building pressure.

I understand what you are saying about pressure and pressurization. Apologies for imprecise terminology, once again. But I don't know how else to describe the phenomena I'm experiencing. I believe I understand why the creosote and moisture are created. I believe the conditions described in my first post burn off the accumulated creosote well enough to keep me from having low draft issues or chimney fires. I do not understand what is forcing the moisture through the tightest of crevices, both sideways and upwards. In some cases it has been forced UPWARDS between the first pipe and the vent collar of the stove. And as I said, I see no deterioration of the welded seams when the creosote/moisture is burned off, so something is pushing that moisture out the side of the pipe. WHAT IS CREATING THIS FORCE?

Based on your previous post, I'll probably replace the single wall pipe with double. And I believe I understand your explanation of why the fans should suck the air upwards, but wonder if that would work in my situation. The ceiling is 16' high. The woodstove is in the living room, and above half the living room is an open loft. With the fans off, it gets way hot in the loft with the living room uncomfortably cool. Near the top of the ceiling in the loft, are several drafty windows. I suspect that it I push the warm air up, too much of its warmth will be lost to those windows before running back down the walls. And with the fans being almost directly above the stove, I've never felt drafty while under them. Todd67's idea about running the fans on low sounds interesting; I'll certainly experiment with that. "You don't want any moving air to cool the single wall pipe. You are making it a condenser inside." If I'm turning the fans off at night, then this should not be an issue, correct?