Wood stove pipe size VS draft

[gsganzer]

I have access to all the dry standing oak I want. It's typically been dead at least 2-3 years if not more. It just depends whether it starts to get termites in it, which will kill a saw chain in short order. Anyway, I try to cut and split it now during the cooler months, but it will be used next year. Once it's split it dries pretty quickly, you could probably cut and split in the summer and it would be dry by the fall. But who in their right mind wants to be cutting firewood in the middle of a TX summer (never mind the fire hazard).

 

[NYlumberman]

Flu temperature is important! It’s a Goldilocks like conundrum. Too cold and the VOCs volatilized from the wood condense in the chimney. Too hot and you can damage the chimney, and maybe burn the structure.
I heated my home, an old farmhouse, for 35 years, exclusively with wood. I also was responsible for the wood fired boilers that heated our dry kilns. What I learned is that wood combustion is chemical reaction that occurs in two stages. The first begins at 451 degrees and combines one oxygen molecule with one carbon molecule, that reaction results in CO and releases about 30% of the potential energy (BTUs). The second reaction occurs at 1200 degrees when a second oxygen molecule is added to form CO2, that second reaction releases 70% of the BTUs.
When you turn down a big stove so the furnace temperature is below 1200 you have incomplete combustion (think smoke).
When you look at a fire, the coals are carbon, the flame is the VOCs igniting.
Water is a byproduct of combustion. The water vapor in flu gas will be the moisture in the wood being flashed off plus the water produced by combustion. Creosote is condensed VOCs and has plenty of carbon available to burn. So ideal flu temp is between 212 and 450 degrees.
All cellulose has 8000 BTU/Lb. bone dry. Most dense Hardwood have 50% moisture green and that reduces the BTUs to 4000 BTU/Lb.
Almost impossible for your stove, fuel and ambient temperatures to be ideal all the time. My solution was two stoves, a big one in the basement and small one in the kitchen both hooked to an insulated masonry chimney with two 8’ flus (laid up with regular cinder blocks and the gap filled with vermiculite).
At 77 I got lazy, and my honey hated it when I went up the ladder to clean the chimney. Upon review…brevity is not my strong suit.

 

[bvanek]

I have to agree that the 6 inch flue drafts better and heats up faster.... and when you get to the top where most creosote is formed (cooler) then it then becomes more of a stove-flue relationship. I have never had creosote build up in the stove itself, so I can't comment on that.

So for me, its a three part system; a manual flue damper, air intake adjustment, and a guy who monitors and feeds the stove(me). My stove has a pretty decent design internally as the air tubes are located at the top....this creates better combustion, maybe some will say re-burn just before it enters the flu...(hotter). Then it depends on whether you leave the stove un-monitored like at night or while away....or if you are around and can make adjustments periodically.

I work the damper and air together and also load the stove with different sizes and types of wood...Fir burns hotter and faster, hardwood slower but leaves more ash.
I am retired so during the colder weather I become the thermostat for the most part. But I can also adjust for allowing to burn through the night as well. The stove design for sure is a factor..but everyone has their own unique system and wood sources so it's not always one size fits all.

Seasoned wood, YUP! at least one year ahead, but depends on the wood, when you cut, and also the typical weather pattern in your area.

 

[dodge man]

I cleaned my flue this last fall and got almost nothing out of it, just light dust. The last time I did it, maybe 5 years earlier I got enough to maybe fill a 5 gallon bucket and inch deep. It was a very dry material like coarse sand. I’m not sure what creosote even looks like??

 

[Rockbadchild]

I cleaned my flue this last fall and got almost nothing out of it, just light dust. The last time I did it, maybe 5 years earlier I got enough to maybe fill a 5 gallon bucket and inch deep. It was a very dry material like coarse sand. I’m not sure what creosote even looks like??

Rhetorical question ??

Its the same for my house almost no need to clean the chimney but I have a hunting camp that produce a ton of creosote, also my garage create some... It is a lot worse for stove that don't runs constantly or runs constantly chocked ... before someone ask the hunting camp wood is 10 to 20 years old and stored in a outdoor shed and we choked it because if not it gets way too hot and there isn't enough window to open.

 

[dodge man]

No I really don’t know what creosote looks like. I’m using a fireplace with an outside air intake. I’m not sure how long my flue is. Maybe 15 feet or a little less.

 

[Rockbadchild]

No I really don’t know what creosote looks like. I’m using a fireplace with an outside air intake. I’m not sure how long my flue is. Maybe 15 feet or a little less.

its a black tar that can become liquid when hot

 

[dodge man]

I’ve got a friend with a wood stove in his basement and I’ve seen the liquid stuff on the outside of his chimney on the roof.

 

[BnRidge]

As a beekeeper with a smoker I got to see what creostote looked like. Fuel was smoldering pellets like what's used in pellet stoves. Nice and dry, yet with black goo oozing out the lid and down the sides. And if I got a nice bunch of coals inside and pumped it good and hard, it would light off just like a chimney fire, crackling and sizzling down the sides. That was one way to clean it. Just like my neighbor - run his stove low and smoldering all fall, then on the first real cold morning fire it up extra hot and it goes off like a roman candle.

 

[drumminj]

As a beekeeper with a smoker I got to see what creostote looked like. Fuel was smoldering pellets like what's used in pellet stoves. Nice and dry, yet with black goo oozing out the lid and down the sides. And if I got a nice bunch of coals inside and pumped it good and hard, it would light off just like a chimney fire, crackling and sizzling down the sides. That was one way to clean it. Just like my neighbor - run his stove low and smoldering all fall, then on the first real cold morning fire it up extra hot and it goes off like a roman candle.

Agree that a smoker is a great way to visualize creosote. I use a propane torch to 'cook' it off, but it's crazy how quickly it builds up when you're purposefully burning low and slow.

 

[jk96]

I cleaned my flue this last fall and got almost nothing out of it, just light dust. The last time I did it, maybe 5 years earlier I got enough to maybe fill a 5 gallon bucket and inch deep. It was a very dry material like coarse sand. I’m not sure what creosote even looks like??

We pay someone to clean ours every year. Part of that is because he's pretty reasonable so I haven't taken up the chore myself, but the other reason is he runs a camera and videos the entire 30ft chase as part of his service, checks all connections, etc. It's good peace of mind for me.

 

[CalG]

No I really don’t know what creosote looks like. I’m using a fireplace with an outside air intake. I’m not sure how long my flue is. Maybe 15 feet or a little less.

Gosh
If I had known, I could have snapped a picture of what was recently swept from my flue when the kids were around for Thanksgiving.

But, I packed the gallon or more in small bags and burnt it all up IN THE STOVE just this past week end.

It burns so nice.

 

[HawkinsHollow]

Yeah I am not a heavy burner either but I get maybe a couple cups of black powdery dust out of my flue each year when I clean it. My new install I am going with double wall in the living space which should help reduce that amount even further. Also something I see happening with the double wall is the ability to burn the stove a bit hotter as the flue pipe will be throwing less heat into the space. Also the addition is bigger with vaulted ceilings and a larger opening into the old house so that should help with heat distribution. Normally in our smaller space with single wall I had to keep it choked down to the point where the secondary burn was minimal or it would heat us out of the place. That single wall threw so much extra heat.

I just check the other day and most of the wood I will be burning this year is 11% moisture cherry and hemlock. There is some oak mixed in there that I am sure has a bit more moisture. I also have an IBC full of ash that is about 20% but that should still burn pretty well.

 

[ponytug]

Yeah I am not a heavy burner either but I get maybe a couple cups of black powdery dust out of my flue each year when I clean it. My new install I am going with double wall in the living space which should help reduce that amount even further. Also something I see happening with the double wall is the ability to burn the stove a bit hotter as the flue pipe will be throwing less heat into the space. Also the addition is bigger with vaulted ceilings and a larger opening into the old house so that should help with heat distribution. Normally in our smaller space with single wall I had to keep it choked down to the point where the secondary burn was minimal or it would heat us out of the place. That single wall threw so much extra heat.

I just check the other day and most of the wood I will be burning this year is 11% moisture cherry and hemlock. There is some oak mixed in there that I am sure has a bit more moisture. I also have an IBC full of ash that is about 20% but that should still burn pretty well.

I'm a little confused. Don't you want the heat out of the flue?

I haven't done that many installations, but I have used single wall in living spaces to radiate heat, and double or triple wall in running flues in old chimneys or enclosed spaces.

I've never had creosote issues, or chimney fires, and I would like to keep it that way. I think that creosote production depends on the stove, the fuel, and the operation of the stove.

All the best,

Peter

 

[HawkinsHollow]

I'm a little confused. Don't you want the heat out of the flue?

I haven't done that many installations, but I have used single wall in living spaces to radiate heat, and double or triple wall in running flues in old chimneys or enclosed spaces.

I've never had creosote issues, or chimney fires, and I would like to keep it that way. I think that creosote production depends on the stove, the fuel, and the operation of the stove.

All the best,

Peter

I guess if you live in Minnesota you might. But I live in Tennessee and "cold" is relative, it seldom get into the single digits. I like to have a fire when it is 30 degrees and the extra heat from the single wall flue overwhelmed our 1000 sqft house. Now we have 1800 sqft. with a more open floor plan but I think the new arrangement is going to be more than adequate for the space and allow me to control the heat better. No more laying on the couch in my underwear in an 85 degree livingroom is the goal.

 

[HawkinsHollow]

There are other advantages to double wall. Lower clearances to combustibles it takes my stove from 10" to combustibles to 8", longer lasting (stainless liner),safer, maintains higher flue temperatures for better draft and less creosote buildup.

 

[deezler]

Yeah I am not a heavy burner either but I get maybe a couple cups of black powdery dust out of my flue each year when I clean it. My new install I am going with double wall in the living space which should help reduce that amount even further. Also something I see happening with the double wall is the ability to burn the stove a bit hotter as the flue pipe will be throwing less heat into the space. Also the addition is bigger with vaulted ceilings and a larger opening into the old house so that should help with heat distribution. Normally in our smaller space with single wall I had to keep it choked down to the point where the secondary burn was minimal or it would heat us out of the place. That single wall threw so much extra heat.

Yeah... that's kinda the point of single-wall. ? Why would you want to burn a hotter fire just to send much of that heat out the roof?

We went with 11' long vertical run of 6" single-wall above my woodstove to vaulted ceiling very purposefully, to gain all the extra BTUs into the house instead of sending them out the roof with double-wall. (and because I am cheap, haha).

You can still burn just as hot and efficient a fire - you just do it for less time if needed. My 1600 sq ft house can get uncomfortably hot as well, wifey sometimes likes to run it up to 80° when shes in a certain mood. but our pattern is typically to start afternoon/evening fires once the sun goes down, temp peaks by 10/11pm, and nice coals remaining in the morning if you need to re-light, but house is still a comfy 65-70°. Just depends if the sun will be out at all for passive heating.

 

[BnRidge]

One problem I saw with single wall was the lack of redundancy and safety. An elbow for instance, double wall has two sets of pipe use to mate sections together, inner and outer, where single wall only has one layer mating with the next section. I was on one job where our task was to among other things vent their wood stove. The owner had used single wall pipe and elbows, didn't have an elbow turned just right to line up with the pipe above, during operation the elbow broke apart and separated creating a disaster of smoke damage. It's difficult if not impossible to have that happen with double wall.
The other problem I see was of the places where buildup could occur, the very top of the chimney was one, where flue gasses could cool the most, and the other was at the top of the inside piping at the ceiling where it tied into the class A insulated pipe above. Not much buildup, but just enough cooling occurred there to produce more than the rest.

 

[HawkinsHollow]

Yeah... that's kinda the point of single-wall. ? Why would you want to burn a hotter fire just to send much of that heat out the roof?

We went with 11' long vertical run of 6" single-wall above my woodstove to vaulted ceiling very purposefully, to gain all the extra BTUs into the house instead of sending them out the roof with double-wall. (and because I am cheap, haha).

You can still burn just as hot and efficient a fire - you just do it for less time if needed. My 1600 sq ft house can get uncomfortably hot as well, wifey sometimes likes to run it up to 80° when shes in a certain mood. but our pattern is typically to start afternoon/evening fires once the sun goes down, temp peaks by 10/11pm, and nice coals remaining in the morning if you need to re-light, but house is still a comfy 65-70°. Just depends if the sun will be out at all for passive heating.

Read above, you live in Michigan and have actual winters. I have 14 acres of trees, if I send a little extra heat up the chimney to have a more comfortable burn I am 100% ok with that.

 

[Larry Caldwell]

There is seldom need to fire the stove hard enough to get the creosote running. But there is always "some" deposits in any flu pipe.

Heck, I cleaned the stuff out of the pellet stove pipe just before the weather turned. Yup, there was "some" build up even in there. (It's warned about in the operators information, so I don't take any blame for it. Creaosote JUST IS! ;-)
I've lived with it for over 40 years, and kind of like the aroma, Reminds me of a smoky Scotch/

Lagavulin anyone?

I think climate must have a lot to do with creosote. We have dry summers here in Southern Oregon. I only use softwood for kindling. All my heating wood is hardwood, typically madrone and white oak. This year I have about two cords of mimosa because a big old tree in my yard died from drought.

I rick all the firewood in log cabin face cords with plenty of space between for air circulation, in direct sunlight. It's all cut before February to avoid sap rising, split and ricked by April. My firewood ends up dryer than a popcorn fart before it goes into the wood shed. Summer humidity is typically around 15%, though hot days drop to single digits. I can see that in the east-central US where humidity is a problem, getting firewood dry would take a kiln. I think water is the big reason in the variation of creosote amounts.

I have a moisture meter that I never use because I know how dry my wood is. Out of curiosity, I just took it to the wood shed and measured. The hardwood measures between 13% and 16% moisture. I have no creosote problem. None. My stove is a 1970s airtight Fisher. I like to think I know how to run it. It has a big firebox, but small fires in the middle are plenty to keep the house warm. I'll stuff an 8" round in there to hold a fire overnight. I depend on large pieces rather than damping down to hold a fire.

I know where the draft needs to be to heat the house evenly, and leave the dampers set there except when starting a fire. To start from a cold box I open the draft wide open and put 2" rounds or splits on kindling. That gives a quick bed of coals to burn my typical 6" splits. One or two pieces is plenty to heat the house. A smoldering fire just doesn't happen.