It might appear as wisps of smoke lazily floating in the room. Or it might be more substantial with puffs of smoke emerging when you open or shut the door on the stove. Outside of it being a bit annoying, it's not a big problem and happens to the most wood stoves at some point. Stoves rely on draft to operate. When your stove leaks smoke, it's typically draft- or maintenance-related.
Stoves and pipes are not typically sealed. If everything is working properly, smoke is drawn up the chimney in a long, continuous breath. There's no need for smoke to alter the course unless something interrupts the flow. Pressure is one factor that can change the course of the smoke. If the pressure outside the stove is less than the pressure inside the stove, smoke will find its way out through joints, cracks or seams no matter how tight the joint. It might be as simple as low barometric pressure outside the home or other pressure-related issues such as the flue vent on the stove in the wrong position. The best way to stop smoke from leaking is to ensure that the stove gets all the air it needs.
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Leaking joints may be routine when you start your stove up each time. There are two reasons why: It's because the pressure in the room is less than the pressure inside the stove, that the chimney pipe is not sufficiently preheated or both. Help the stove to operate at its best by cracking a window or door near the stove during the initial fire-up. It allows the stove to gulp larger quantities of air faster as it burns the kindling and paper at a higher rate than it normally does when only coals are burning. When the fire is established or after about 30 minutes, close the window or door and the stove shouldn't smoke. Another cause of smoke during the initial fire-up may be a cold stovepipe. Hot smoke resists entering cold pipes and often leaks out through joints at this point. Hold the stove door open about an inch to allow the kindling and paper to burn adequately and get hot. As the stovepipe gets hot, it draws the smoke up and out, preventing leaks into the room.
Air movement through the stove is called draft. Even if your stove has pipes or joints that don't fit tightly, with good draft chances are that your stove will not leak smoke. Draft is controlled by the vents on the front of the stove, and the flue vent on the chimney pipe. If your stove is leaking smoke from either of these, turn the knob or knobs on the front of the stove counterclockwise to allow more air into the stove. This adds more air to the combustion, causing less buildup of smoke inside the stove, and moves smoke and air through the stove faster. If the stove continues to leak smoke, it might be because the flue vent is not open or only partially open. Locate a large knob on the stovepipe -- typically made with coiled wire -- about 6 inches up from the point where the stovepipe emerges from the stove. The coiled wire handle operates a flap inside the pipe. If the flap is turned sideways, it blocks the flow of air coming up the chimney. Turn the handle 1/4-turn to open the vent. The stove should stop smoking immediately when the flap or flue vent is aligned with the chimney.
If your stove has adequate draft from the front and the flue vent is open but the stove still leaks smoke, it might be because the stovepipe is dirty. Dirty pipes can cause the flue vent to stick or clog. Dismantle two or three sections emerging from the top of the stove. They are typically held in place with two or three screws. Remove the screws, lift off the sections and use a wire brush scrub off the creosote -- which is a black, crystalline material -- from the inside of the pipe. Then put the pipes back on. If the stove still leaks smoke, hire a professional to clean the remainder of the pipe penetrating through the roof or sidewall. If you positively have to stop all leaks, you can also use stovepipe compound on the joints. Dismantle the sections, add the compound to each part and reassemble the pipe, or you can add pipe joint compound to the joints when the pipe is in place. It's not real pretty, however, and usually unnecessary if your stove is in good working condition with all the vents open.