A Clogged Chimney at a Wood Heated Alaska Cabin

Stove pipe creosote, 3 months' use

Note:  After reading this article, readers may ask themselves, “How long has it been since I cleaned my chimney?

 

Our off-grid log home is heated by a Drolet wood stove that burns spruce and birch almost 24/7 during the coldest winter months, up to 40 logs per day.  Fast, hot fires burn more cleanly than do slow, cooler fires because of the speed and temperature of the smoke that rises and exits through the stove pipe.  Wood that is less than optimally dry* or letting fires cool down, go out, and then restarting them frequently contribute to smoke conditions that coat the interior of the stove pipe with creosote and ash.  This builds up like cholesterol in arteries, narrowing the circumference through which the smoke escapes.  A clogged chimney is a dangerous chimney.  Dependent as we are on heating our home with wood, these issues warrant frequent maintenance to ensure a clean burn, clean air, and a safe home. 

On the first of every month, my husband opens the exterior “chase” and shoves upward an extendable chimney sweep, which, with its thick circle of metal bristles, scrapes off creosote.  The flakes shower down, looking like greasy, shiny bits of charcoal.   We sweep up the debris and dump it in the outhouse hole, not wanting it in our gardens, yard, or water table.

Still, this task is not enough to ensure a clean chimney and part of the problem may be our less than

Wood stove with hot water tank

optimal design.  We have an interior metal tube that rises about 4.5 feet from the wood stove and then exits the structure at a 90 degree angle, to ascend 2.5 stories above our metal roof.  The horizontal section slows the smoke and collects debris (see photo above).  Every spring cleaning, we dismantle the interior pipe and vacuum it out.   Another problem is much higher, where it is hard to address.  Many chimney tops, including ours, are encircled with several inches of mesh wire to retard sparks and deter birds from nesting within a quiescent, summer chimney.  This mesh is topped by a flat, metal cap to keep out rain.   

With a hot fire, the smoke quickly ascends the 2.5 stories before it cools.  A cooler fire means cooler, slower smoke and more creosote build up.  Even in mid-winter, when one would think that our fires are very hot, we used to see salmon colored creosote icicles dangle from the mesh, eventually crashing onto the back porch, leaving a distinctively resinous scent that we did not want our boots to carry inside. 

Back of cabin, hot tub to right

Every summer, Bryan climbed our longest ladder with a poking tool that he jury rigged out of a paint roller to hammer and poke at creosote accretions that clogged the mesh.  I stood below, holding the ladder, wearing a hard hat to protect my head from the rain of hard chunky bits that he dislodged.  After complaining about this task to a wise friend in Wasilla, we heard the directive:  “Remove the cap.  You are in more danger of smoke damage than of a bird nest.”  Heard and noted.   So, two summers ago, Bryan ascended the ladder with tin snips and succeeded in cutting out the section of mesh that faced him, and two of the four tines that held the cap in place.  However, he could not reach those on the far side of the chimney.  So he descended the ladder, got a hammer, and rammed the cap up and back at a rakish angle.  The chimney now had a “mouth” to which no creosote could cling.    This helped for two years.

However, since then, we have been burning beetle killed spruce inside, rather than birch.  It creates less ash in the wood stove, which is an advantage, but it produces fewer BTUs (British Thermal Units) than birch, meaning that the heat per log is not as high.  Within the past month, we have had to contend with two times when the smoke in the firebox could not ascend the stove pipe.   This could be dangerous. At the end of December, we let the fire go out and then dismantled the interior chimney tube.    With spoons and a shop vac, we removed about 2 gallons of ash and creosote and swept the upper stove pipe, too.  This week, my husband was dismayed to discover, during a midnight check on the firebox, that the smoke within was swirling, not drawing.  The temperature gauge on the pipe 2 feet above the wood stove read a meager 150 degrees. 

Creosote clogged cap and mesh,

 

 upside down

Before the cooling smoke could escape into the house (heat rises, cool air sinks) as happened several years ago, described in a prior February blog, Bryan donned his parka, hat, gloves, and boots, along with a bright headlight.  He opened the exterior chase of the stove pipe, quickly inserted the chimney sweep and shoved it so hard up the chimney that he rammed the rusting metal cap off altogether!  It careened down into the snow.   By the time he dismantled his tool and re-entered the cabin, the stove top thermometer had doubled to 300 degrees when the firewood reignited and burned brightly. 

The attached photo shows the gross looking creosote gunk that coats the mesh, blocking air flow. 

From now on, we may get some rain in the chimney, but I will feel safer all winter, and safer for my husband.  I was always nervous when he climbed that long, steep ladder to stab and cut the chimney top. 

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* Our wise friend in Wasilla also gave us the gift of a handheld, battery powered gizmo make by a company called General to measure how dry a log is.  You simply stab two metal probes into the wood to get an immediate moisture reading.  The closer to zero the better.  A reading of 13% is considered medium, not optimal.  For this reason, storing firewood under a tarp or roof is obviously better than leaving it outside uncovered.  Trying to burn newly cut wood is even more fruitless.  Readers:  if you pay good money for a cord of wood delivered to your home, ask the vendors to measure its dryness.  They know.  You may want to spend $20 - 30 for a tool like ours to confirm the wood dryness upon delivery, or before burning some inside.