Farm Life: Wood Stove Flues

Now that you have selected your wood to cut and season, and have run a few fires in your wood stove, consider how to maintain the flues.  This is not the romantic aspect of a wood fire, but more a Charles Dickens gritty chore.  The demon of wood stove flues is creosote.  This is the black, gummy stuff that causes chimney fires.  If you burn wood, you will generate creosote.  If you do not clean the stuff out of the flues, your insurance company will not be happy.  

Jotel, cast iron stove downstairs

First, recognize where creosote comes from.  It is the residue from tree sap.  Pine wood is so full of the stuff that might as well burn all of your furniture, siding, studs, flooring, and roof, as you will burn your home down burning pine in a wood stove.  Hardwoods also generate creosote, but usually when the wood has not been seasoned.  Green wood is the worst, if you can get it to burn in the first place.  More often the culprit is sort-of seasoned wood.  I try to stay two years ahead of needing to burn wood.  Thus, the wood that I am taking down now, I may take a year to cut and split… or wait for visitors to help me with :).  Then, I like it to sit for another year in a pile or the wood shed.

You can purchase moisture meters now to test your wood, but air drying for a couple of years is usually sufficient.  Be careful about purchasing “seasoned” wood without seeing it.  I heard someone once say that the difference between the wood he was selling being seasoned or not was whether it was September.  In the summer, he sold wood for a lower price as unseasoned, with the expectation that the buyer would not burn it for a few months.  In fall, the same wood was seasoned and commanded a higher price.  Seasoned wood will usually look dry and often grey.  Pick up a seasoned and unseasoned log of the same type of wood and you will know the difference in weight.

Yes, that is 200 - 300 C

Even when you burn seasoned hardwoods, you will develop some creosote.  This occurs in the cooler lengths of your flue pipe, usually near the outside, exposed sections and top.  Creosote turns into a gas when hot, travels with the smoke, and then cools quickly on the inside of the pipe and chimney cap.  Also, running the fire at too low of burn level will allow more creosote to deposit.  Getting a flue thermometer is a good investment to monitor your burn tempertures.  When you get a good, hot fire running you will hear a crackling in your pipe, which is the creosote heating up again.  If a you hear a freight train instead, call the fire department and hose down your roof against a chimney fire.

You can purchase commercial chemicals at wood stove stores and farm stores that “harden” the creosote.  These generally instruct you to toss in a tablespoon or so every week.  My neighbor swears that aluminum beer cans do the same.  I’m not sure what aluminum oxide does, or maybe he is just getting rid of his six pack before the wife finds it.  In any case, these products do work.  However, they do not mention that after the creosote hardens it will start to follow gravity and fall down your flue pipe into the top plate of your wood stove.  Wood stoves usually have a ceiling plate that prevents the flames from going directly up into the flue.  This also acts as a catalytic converter when it heats up and the gas from the fire sweeps around this plate.  However, as the creosote builds up, it slows the flow of the hot exhaust, reducing the efficiency of the stove.  This reduces the burn temperature, generating more creosote, and possibly smoking up your home.

Thus, regardless of the other measures that you have taken, you will need to clean the flue.  We have two wood stoves, with exposed flue pipes for the country atmosphere.  The upper stove has 14′ of pipe to the ceiling, then 4 feet extending above the roof.  The downstairs adds another 6′ of pipe, making about 24′ of pipe lenth.  This is important to calculate how long of a chain you need.  Another useful tool is a chimney brush, which has to be the same diameter as your pipe (usually 6″ or 8″).  You can add extension handles on these to reach the length of your pipes.

cook stove upstairs, plus two flue pipes

I usually clean my flues twice per year: once on a summer morning, and once mid-winter on a day of thaw when we can let the wood stoves burn out over night.  Keep your safety common sense on for this project, as you need to climb on your roof.  Once up there with your tools, remove the stove hoods.  I keep a second set on hand to just replace them.  Then I can clean the hoods and store them for switching out the next time.  Then lower a length of heavy chain into your pipe and start a turning motion.  The dogs hate this as the whole house rattles with the chain going around the inside of the pipes.  The chain breaks of the larger flakes of creosote.  Then, use the chimney brush, adding lengths of handle to get a far down as possible.  Gravity will take care of the rest.  Put the clean hoods on the flue pipes and collect all of your tools.

In winter time, my last chore is to vacuum out the creosote that fell down.  I added a T-section of pipe at the base of the flue pipe.  I can reach in with an old vacuum hose and suck out the pile of creosote flakes that fell from the cleaning.  Cap off the T and light up the stove again.

  In summer, I have a more extensive cleaning process.  Upstairs, I remove the pipe, cleaning each section with the chimney brush.  I store these off the stove for the summer.  The open flue now become part of our passive cooling system.  The heat of summer rises up to that high point in the ceiling, exits out the open flue, and draws cooler air up form the basement.  Life without A/C.  I also remove the section of flue from the downstairs stove to the ceiling, clean this separately and give the top of the stove a really good vacuuming.

Now we can enjoy a nice, toasty fire in winter.  Wood stoves are kind of like safe sex.  Do your homework, have the right tools, and keep it clean.  Then have all the romance you can stand.


About hermitsdoor

Up here in the mountains, we have a saying, "You can't get there from here", which really means "We wouldn't go the trouble to do that". Another concept is that "If you don't know, we ain't telling." For the rest, you'll have to read between the lines.
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8 Responses to Farm Life: Wood Stove Flues

  1. The Vicar says:

    “Wood stoves are kind of like safe sex” – By this do you mean that they are best enjoyed in a monogamous relationship with a lifetime commitment?

    • hermitsdoor says:

      I would put that under doing your preparation work ahead! Getting cozy with someone whom you do not know, and may not know after tomorrow, is like burning an unidentified type of wood in your stove… risky business. Hope that clarified things.

  2. Vicar's Dad says:

    I don’t have a wood stove, and my gas heater does not seem to generate creosote in my chimney.

    • hermitsdoor says:

      In your location, with few trees available to harvest, a natural gas heater makes a lot more sense. You spent enough time on our roof when I was young. Flat ground is a better location now.

  3. Mother Suzanna says:

    After you left home, we had a fireplace insert for many years until one day I decided to lie down on the carpet in front of the fireplace, which had a window, and the fire was doing strange things inside the fire box. The flames where way too big and bright! I had just called the fire department when a LOUD knocking came at the front door. A neighbor had seen the flames shooting out the flue of the chimney! That’s when we had a natural gas log insert put in with a double flue which did not require yearly cleaning. At least the old homestead didn’t burn down that day!

    • hermitsdoor says:

      I recall your story about the chimney fire. I recall the pine trees that came out of the back yard years ago too. I recall cutting up the dry Christmas trees and burning the branches in the fireplace. Yikes!

  4. Barneysday says:

    Another great piece. My grandfather had a full sized Case tractor, which ran a huge saw in the fall. The ritual at that time of year was for the extended family to spend a day or more cutting wood, which 3 families burned for heat. Here I was, less than 10 year old, working next to this whirring saw blade of at least 36 inches in diameter. My job was to hold the pieces as my Grandfather pushed them through the cut. I then would throw them behind me, onto his dump truck. As I recall, the ladies would work all morning to make a huge dinner (as we called the mid-day meal) while all the men and boys were involved in the gathering or cutting process. Working in the cold day, sunup to sun down, I can’t recall how many chords we cut, but it had to be a lot.

    They actually were great memories.

    BTW: My grandfather swore by this method of telling seasoned wood from wet wood. Pull two similar chunks out of the pile, and hit them together. Seasoned wood would respond with a solid “clunk”, unseasoned would make a dull thud. I’ve used his method for years, with great success.

    Thanks for this rural series, it brings back great memories.

    • hermitsdoor says:

      Your grandfather had a good method for telling seasoned wood. I have noticed the difference in clunk vs thud, but had not put that together. I have to try clunking some wood next time I bring it in.

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