How To Start A Chimney Fire (Or Not)
By Jonathan Smith
From Issue 17: Winter 2013
As I was eating breakfast on a bitter cold morning a few years ago, I heard the fire alarm in the distance and wondered if somebody was experiencing a chimney fire. I began to think about how I could intentionally start a chimney fire in my own house. Ok, I admit this sounds totally absurd, but could a little reverse psychology prevent a chimney fire or two?! You see, one of my goals in business is to improve people’s overall wood burning experience by helping them limit dangerous creosote forming in the chimney. A chimney without excess creosote is sort of like having a gun but never being concerned about it accidentally firing because there is no ammunition available for it.
So here’s what I would do if I wanted to have a chimney fire! We don’t have to do ALL of these things, but if we want to have the best chance at “success,” we need to do as many as possible!
1. First, I would only buy my “seasoned” wood when I’m just about ready to burn it, OR, if I buy my wood in advance, I would store it uncovered on the ground so it’s most likely to have lots of water in it. Dense hardwoods are best because they hold lots of moisture—no pine or evergreen—they can burn too hot and clean. (Remember, we are trying to burn the best dirty fires!).
2. Next, I would choose an old wood stove that is not EPA compliant—a real “dirty” burner …a nice creosote factory, if you will. (We can, of course, still have a chimney fire with an EPA compliant stove that is ehhh… “properly operated” for a chimney fire!)
3. Then I would have an exterior masonry chimney with a “dinosaur-age” terra cotta flue liner that is larger than needed, such as a fireplace-sized flue. For creosote buildup, bigger is better!!
4. I would develop a fear of getting the stove hot. A cooler fire usually results in a lot more unburned smoke and a hotter fire burns up more of the smoke in the firebox so, for now, no cardboard box burning! I must have poor combustion with lots of smoke coming out of the chimney and must make sure to set the air intake on a low level all the time.
5. Then we wait about two months for plenty of creosote build up and, on a really cold night when I’m a bit chilly, I would turn up the air control and do some nice cardboard or pizza box burning!
Finally, I’d watch the beautiful flames and sparks shooting out the top! It’s the express route to a beautifully clean chimney.
OK, that was fun. Now let’s PREVENT that chimney fire! The numbers in these two columns correspond to each other …
1. Even seasoned wood, left outdoors, has too much moisture content, so we order our wood about a year in advance and stack it in ventilated sheds by the first day of spring. Tarps keep the rain off wood that has already been dried, but tend to trap moisture in wet wood. Burning pine by itself does NOT create creosote! This is a very common myth. It’s true that hardwoods are denser and produce more heat, but it’s not the TYPE of wood, but the DRYNESS of the wood that matters most with creosote accumulation.
2. Even though newer, EPA compliant stoves have been designed to burn cleaner and burn less wood, they can still burn dirty on wet wood with the air controls choked down.
3. Most masonry chimneys are built with the poorly insulated, terra cotta lined flues that have been used for over a hundred years. Creosote forms when smoke, rising up the chimney, cools and condenses on the flue walls, so an insulated liner is best, especially on outside chimneys that are exposed to the cold. Smoke that stays warmer does not condense as much, and warmer smoke is more buoyant and will improve draft performance. If you have a masonry chimney with a terracotta liner consider having an insulated stainless steel liner installed—and bigger is not always better! A flue sized properly to the heating appliance is best.
4. At first, we burn the fire hot and high with the flue full open. Depending on the type of stove and whether you are starting from a cold stove or reloading a hot one, that could be anywhere from ten minutes to an hour and a half before you close the damper and reduce the air. People develop their own technique—it’s more of an art and a judgment than an exact science—but if you like, there are cheap magnetic thermometers for the stove top that can tell you if you are regularly getting your stove HOT, say to 700 degrees. As with anything, we don’t go to extremes. Warping of a stove is rare, but can occur when someone leaves the air intake on high, then walks away and forgets about it, especially if it’s done repeatedly. Moderation is the key.
5. It is very possible to build up enough creosote for a chimney fire in as little as a month. If you are uncertain, have the chimney inspected mid-season, and of course have it swept once a year.
6. Occasionally check to see how much smoke is coming out of your chimney—the less, the better! If you do have a chimney fire, call the fire department. In the meantime, try to choke the fire of oxygen by closing any air controls on the stove. A chimney fire in a fireplace can be particularly dangerous because it’s harder to choke. Chimney fires can exceed 2,000 degrees, and with the proximity to combustible house framing materials it’s easy to understand how disaster can strike quickly. Also, sparks landing on a combustible roof is not always a good idea!
What it all comes down to? Burn only DRY wood, and get your stove good and hot on a regular basis. May you stay safe and warm during this winter season.