Heating with Wood Part XI Cleaning the Chimney

Chimney cap some creosote glaze and soot. This type of cap swivels with the wind.

Stoves are meant to take the heat. Chimneys aren’t. That’s why flammable creosote in a chimney is problematic. As the Chimney Safety Institue of America (yes, there is one) points out, clean chimneys don’t burn.

It’s spring. Trees are leafing out. Rhubarb and garlic are up in the garden. Finches are in the willows. Wouldn’t this be a good time to get up on the roof on a beautiful day and clean the chimney? Really. Look, you’ve got to do it anyway. If you do it now, when you light a fire on a rainy day to take the chill off, you won’t be worried about the winter’s collection of creosote in the chimney. Also, next fall when it’s getting cold and roof’s icy you won’t be saying, “Dang, I really should have cleaned that thing.”

What is creosote?

Burning wood exhausts a mix of water vapor, unburned carbon, and volatile gasses. At high stove temperatures most of this burns away or is carried up the chimney. When the fire is cool and temperature of the smoke falls below 250 degrees F the mix begins to condense into creosote on the sides of the chimney. Creosote is mostly methanol (wood alcohol), acetic acid and carbon. When the temperature goes below 150 degrees F creosote becomes thick and sticky like tar which collects soot as it bakes onto the chimney walls. Creosote can be flaky, which is easy to brush off, or if it goes through heating/cooling cycles, can become a thick layered glaze which is really hard to get off. In addition to being a fire hazard creosote can become so thick it impedes the stove draft, which decreases stove efficiency and increases smoke, leading to more creosote.

The chimney cap is a necessary obstruction where smoke is coolest and a place that you can sometimes see glazed creosote from the ground. A swivel chimney cap—one of those metal things that looks like a conquistador’s hat—that turns away from the wind like a weather vane, is a great item but if it gets a heavy glaze of creosote it stops turning and instead funnels wind directly down the pipe into your stove. Which makes it real hard to light. Smoke pours out into the room. Whatever the weather, if that’s going on you’ll have to get on the roof and free the cap before you curl up with a cozy fire and a good book.

How to clean a chimney yourself

Looking for a chimney sweep in Juneau can be like Mississippi John Hurt singing a gospel song, ‘Ain’t nobody here can walk it for you. You got to walk that valley fo’ yourself.’ Years ago after having mediocre, and expensive, service by a local entity (who I’m told is not in the business anymore) and finding no one else around I learned to walk it fo’ myself. It’s not rocket science.

To clean a round metal wood-stove chimney you need:

*a stiff poly (not wire) chimney brush the same diameter as the inside of the chimney You want a poly brush because wire can score the stainless steel, increasing surface area and the acid in creosote can corrode the metal. Some poly brushes are wimpy and will remove soot but not creosote so get a stiff one.

*enough fiberglass extender rods to get through the stove pipe (they’re four feet long and screw into the brush and each other)

*rubber gloves

*dust mask

*glasses or safety glasses

*putty knife

*small bucket

*7 inch diameter hose clamp (for a six inch diameter pipe)

*sturdy plastic bag.

*can of flat black, stove spray paint rated for high heat.

*drop cloth

*bright flashlight

*screw driver

Inside the house: 1) put the drop cloth around base of stove. 2) At some point in this operation you will need to take off the black stove pipe between stove and the ceiling to get out the creosote. There are two options of when to do this: a) leave pipe on, go up on the roof and plunge the whole chimney and pipe as a unit then take off the pipe and clean out the creosote at the bottom. The drawback to this is, if there’s a lot of creosote it will be backed up into the pipe and spill out when you remove the pipe. option b) take the pipe off first, carry it outside (holding it horizontal so stuff doesn’t spill out on the way) and clean it outside of the house. This is a good time to touch up the pipe with paint if it needs it. Back in the living room there will be a piece of the chimney pipe sticking down through the metal plate in the ceiling where the pipe was attached. Put the plastic bag over that with room for a few gallons. Secure the bag with the hose clamp. Some people use bungee cords. I don’t because the clamp is more secure. If that bag were to pop off with a gallon of creosote inside it would be a mess.

Bag of soot and creosote.

3) As far as taking off the black pipe itself, this is how ours works. It has a collar holding the top where it meets the ceiling. Each joint between pipe pieces except that top one has three screws (that’s a fire code thing). We take the collar off with the screw driver. Take out the three screws from the middle section of pipe. The upper section fits inside the lower section. Slide the lower section up out of the stove about four inches. Pull down and the top comes away from the ceiling. Easy.

On the roof: Remove the chimney cap. Ours just pulls straight up and out; no tools needed. Inspect the cap. If the metal’s discolored or deformed that’s an indicator that there has been a chimney fire that went unnoticed. Clean the cap using the putty knife if necessary. Put the scrapings in the bucket. The cap will try to roll off the roof when you set it down. Next put one of the fiberglass rods on your brush. Plunge the chimney a few times. Attach the next rod and repeat. Same with the next rod until you reach the bottom. Once the chimney’s cleaned and the creosote is removed shine the light down for a visual inspection. You can also put the light on a string and lower it down. Look at it from below as well. Then put everything back together. If you need to touch up the paint when the stove pipe’s back in place, spread some newspaper on top of stove and hold a large piece of cardboard behind the pipe so paint doesn’t get on the stove or wall. There. Done. You are a chimney sweep.

How to reduce creosote buildup

All burning wood puts out creosote. Softwood puts out more than hardwood which does not matter around here since softwood is what we’ve got. A thing that makes a difference for us is that seasoned wood puts out far less creosote than green wood. Also, the stove’s air settings are a major factor. Back in the 1980’s Jay Shelton did tests for Mother Earth News. While pine gave off about four times as much creosote as oak, he said, “We observed up to 48 times more creosote with a smoldering fire than with a hot flaming fire using the same fuel.”

If you know there’s a lot of creosote in the stack, don’t try to build a big fire in the box to burn it out. A chimney fire can get up to 2000 degrees, which can warp the metal or cause problems with the surrounding structure. Better to just go up and brush it. For spring, summer, and fall fires, when you are just doing short burns to take the chill out of the house, use smaller pieces of wood and fill the box less than a third full. That will reduce creosote buildup because, with a box full of big pieces of wood, people tend to close the dampers so the heat won’t blast them out of the room. With less air the wood smolders.

How often to clean?

People are all over the place on this. Some never do it until there’s a problem. Others do it quarterly. Some do it after each cord burned. Here at Woodshed Manor we do it every spring when trees are leafing out and finches are in the willows.

Some resources

*The Facts About Chimney Fires. Chimney Safety Institute of America website

*Homeowner’s Guide to Chimney’s Fireplaces and Woodstoves. by Jim Brewer and Ashley Eldridge. National Chimney Sweep Guild website

*The Creosote Problem: Chimney Fires and Chimney Cleaning by Thomas Karsky, University of Idaho Cooperative Extension Forestry Information Series. Wood as Fuel vol 6.

*Mississippi John Hurt – You Got To Walk That Lonesome Valley https://www.youtube.com/watch?v=85BvT5X6WSo