Wood Burning Stove Problems

 

When working correctly a wood burning stove can be a cost effective and efficient source of heat for your house. However the frustration caused by a stove not working as it should, can quickly detract from these benefits. Common problems include: smoking, mechanical problems, creosote, smells and animals. Below is a guide to help you address these problems before calling out a specialist.

Smoke

Smoke is associated with the most common problems experienced with wood burning stoves. Often this is down to issues with the flue system or incorrect use. There are a number of smoke problems that can appear -  smoky start-ups, smoky endings, constant smoking, smoking during windy periods, smoking on rainy days and smoke in other areas of the house.

Smoky Start-ups

A smoky start up is when the stove smokes when it is first lit, then after a few minutes begins to work properly. The following things should be considered:

Wood Burning Stove Dampers - Inside a wood burning stove or in the pipe leaving the stove, generally you will find a damper. A damper consists of movable metal plates that help control the flow of smoke and gasses. When the stove is lit, the damper must be fully open, to allow maximum draft for start-up. This is when the highest concentration of smoke is produced. If a damper is left slightly or completely closed when lighting, the stove will most likely smoke.

There are two types of damper:

 

• By-pass dampers. A by-pass damper is a moveable metal plate inside the stove, usually located at the top rear of the firebox near the flue collar.

 

If your stove has a by-pass damper, you should be able to see it by looking inside the stove. When the damper is open, smoke by-passes the normal exit route, moving directly out of the stove into the stovepipe and chimney. When the damper is closed, smoke is re-routed through a system designed to increase the efficiency of the combustion of the smoke.

 

• Pipe Dampers. A pipe damper is a metal valve installed inside the stove pipe, which can be moved using a handle on the outside of the pipe. Turning the handle opens or closes the plate. It should be noted that pipe dampers are designed to allow some movement of smoke and gasses even in the full-closed position.

 

The purpose of a pipe damper is to retard the flow of combustion air, smoke, and gasses in the stove by reducing the flow of smoke and gasses into the venting system. Most DEFRA approved stoves are designed to be used with no pipe damper in the pipe or at the stove collar. If your stove has either type the damper must be in the open position during startup. Once the fire is established, the burn can be controlled using the damper.

 

Cold Flue when lighting. Warm air rises and cold air sinks - for a chimney to operate properly, the flue must be warm compared to the air surrounding it. This will cause the smoke to rise through the chimney and leave the house. If the flue is cold when the fire is lit – as is often the case, especially when an external flue is used, smoke might be pushed back into the house. Once the flue begins to warm up, the chimney will start to draw the smoke out. To prevent this, the flue should be primed prior to lighting the fire. This is quick and easy to do:

 

HOW TO PRIME THE FLUE - Roll up a piece of newspaper, light one end, and hold it in the firebox of the wood stove, up near the flue collar. Don't stuff it into the flue collar - you want the ashes to stay in the stove, and not clog the pipe. You might need to burn two rolls of paper. You will soon feel the draft reverse, as the warm flue gasses start to move up the flue. Once you have primed the flue, you can light the fire. If the newspaper trick doesn't seem to be working, try leaving the stove door open for half an hour or so, allowing heated room air to gradually reverse the flow.

Blockages. Sometimes, a smoking problem can be caused by blockage of the flue. Creosote build-up, animal nests, leaves/debris, or internal collapse of the chimney lining or brickwork can cause blockages. If you think your chimney may be blocked, make an appointment to have your chimney inspected.

 

Smoky Endings

If your stove seems to work okay once you get it going, but smokes when you are done using it, as the fire is going out, here are some possibilities.

 

External Flue System- Chimneys built on the outside of the house are notorious for smoking problems when the fire is low. While chimneys built up the middle of the house have the house to keep them warm, exterior chimneys cool quickly, since they are exposed to the cold weather. So as the fire dies and less heat is emitted to keep the flue warm, the draft tends to weaken, creating the potential for smoke spillage. But usually when a stove smokes at the tail end of the fire, a cold, exterior chimney is a contributing factor, but not the only factor. Since it is generally impractical to build a new chimney inside the house, first consider the other possible factors. If you can eliminate some other problems, the reduced draft that the cold chimney causes might no longer be critical.

 

Over-Sized Flue. For wood stove venting systems, bigger is not better. An excessively-large chimney flue requires more heat to keep warm, and cools more quickly than a properly-sized flue. Lower flue gas temperatures in large flues cause reduced draft, increased creosote build-up (since the smoke tends to cool and condense in the flue), and the potential for smoking problems, especially when the fire is not burning high.

 

It is fairly easy to determine the minimum and maximum chimney flue sizes for a wood stove:

 

• Minimum Flue Size: Unless specified otherwise in the manufacturer's installation instructions for your stove, the flue must be at least as large as the flue collar on the stove.

• Maximum Flue Size: Current standards and regulations generally recommend that the chimney flue be no larger than three times the cross-sectional area of the stove's flue collar. Anything over three times larger will very likely result in serious venting problems, not to mention the risk of chimney fires due to increased creosote buildup in the flue.

 

What size chimney flue is best?
Ideally, the chimney flue should be the same size as the stove's flue collar. Whether or not the stove can tolerate a larger flue (and how much larger) depends on the type of stove and how you use it.

Air-tight stoves, which allow the user great control over combustion air, often vent lots of smoke into the chimney, often at relatively low temperatures. Since smoke moves more slowly and cools more quickly in these large flues, an over-sized flue can be a real problem, even if it falls within the less than three times rule. It is best to have a flue close to exactly the same size as the stove's flue collar.  

DEFRA approved stoves tend to vent much less smoke and much less heat into the chimney. The reduced smoke output tends to ease the problem of creosote buildup, but the reduced heat vented to the flue means less heat to keep the flue warm, and therefore less draft in a large flue. These stove models range in draft- sensitivity from very draft sensitive (for which even a slightly-oversized flue is a problem) to not at all draft sensitive (for which an oversized flue isn't such a problem).  The solution to smoking problems caused by an over-sized chimney flue is to re-line the flue using the correct liner size.

 

Depressurized House- Inadequate available air in the house can create smoking problems, especially as the fire burns low, reducing the heat vented into the chimney.

 

Constant or Erratic Smoking

Constant or erratic smoking from the stove can be down to a number of stove issues:

 

Under-sized flue. Current regulations require that unless specified otherwise by the manufacturer, the chimney flue should be at least as large as the flue collar of the stove. The stove collar on any given model of stove is sized in accordance with the stove's design. That model needs at least that much vent capacity, to vent the combustion products it emits properly and safely. Under-sized flues lack this needed capacity, and often spill smoke into the home. Yes, some stoves function with under-sized flues without spilling smoke. But even if the stove doesn't smoke as a result, bottle-necking the smoke and gasses into an under-sized flue could create a fire hazard, and should be avoided.

 

Blockages. If the flue is even partially- blocked, reducing the effective venting capacity of the chimney, the stove might spill smoke. Soot and creosote buildup, animal nests, leaves and debris, or internal collapse of chimney liners or brickwork can cause blockages. If you think your chimney may be blocked, or if you haven't had it checked by a chimney professional within the past year, make an appointment for a chimney check. Your chimney professional is qualified to identify and correct chimney blockages, and to check your chimney for other hazards as well.

Multiple appliances connected to the same flue. In the past, people often connected wood stoves to flues already serving a furnace, fireplace, or other appliance. Newer standards require that the wood stove have its own, separate flue. There are several good reasons for this:

1. Soot and creosote from the wood stove could potentially block the flue, causing toxic exhaust from another appliance to enter the home.
2. The draft to one appliance can be severely affected by the other appliance.
3. Exhaust products, when combined, could react adversely.

 

Backpuffing. Backpuffing is a specific type of smoking problem often misdiagnosed as a wind-induced problem or stove defect. Jets of smoke emitted from a wood stove, caused by the ignition of a buildup of combustible gasses in the firebox.
In short, backpuffing is caused by an inadequate flow of oxygen into the firebox. Instead of burning steadily, combustible gasses build up in the firebox and periodically ignite in a small explosion, forcing smoke out of the stove through every available opening, including the air intakes.

What might cause your stove to backpuff? Generally, shutting the air controls down too far, starving the fire of oxygen, AND:

 

either using super-dry wood, like pallets or kiln-dried wood blocks, which burn very rapidly, emitting too much combustible gas too quickly or using firewood that is split very small, which also burns too rapidly, creating an excess of combustible gas in the firebox.

 

Backpuffing is fairly easy to diagnose: Try opening the air control on the stove. If the smoking stops, it is very likely a backpuffing problem. Of course, you shouldn't over-fire the stove, either. If you have to open the air control to the point that the stove will overheat before the backpuffing stops, then reconsider your firewood supply. Either get a new load of properly-seasoned wood, or try mixing less- dry or larger pieces with the super-dry or small-cut pieces.

 

Smoking on Windy Days

Some stoves seem to work okay except on windy days, or if the wind is coming from a specific direction. Consider the following:

 

Chimney is Too Short. Chimneys must meet specific requirements for height compared to the roof of the house.

1. If the chimney is too short compared to the roof, wind moving across the roof will either blow directly into the chimney, possibly forcing smoke into the house, or create a high-pressure system around the chimney, also causing the potential for smoke spillage.
2. If the overall height is inadequate, the chimney will be prone to spillage from wind, since a short column of hot air produces a weaker and more easily- disrupted draft, and more likelihood of draft reversal than a tall column of hot air.

Often, simply adding a few feet to the chimney will solve the problem. But consult with a chimney professional first, to determine the practicality and cost of increasing the chimney height. Your chimney professional will also check the system for other possible causes, some of which might be more critical than the chimney height.

 

Oversized Flue. Very large flues, which sometimes have problems even on calm days, are often more prone to wind-induced downdrafts, since the draft is often weak to begin with. Especially when coupled with a short chimney, an oversized flue can be a serious problem on windy days.

The best solution is to re-line the flue with the correct liner size; however, if you don't have a chimney cap, and the problem is not too severe, try a cap first, in an effort to deflect some of the wind.

 

No Chimney Cap. A chimney cap helps deflect wind. Some are specially designed as downdraft-deflectors. If you don't have a cap, get one. While a standard chimney cap - a lid of some sort, on posts or a mesh base  is not specifically designed to deflect wind, merely having that lid above the opening will help reduce some wind-related smoking problems.

But if your downdraft problem is severe, a downdraft-deflector cap might be a better option. These caps have a baffling system, generally wide bands of metal curving up over the chimney top that re- direct the wind and in some cases actually create a slight increase in chimney draft when the wind strikes the cap. Before you buy a specialized cap, have your chimney professional check the chimney to determine if your chimney will likely benefit from a special cap, and which type is best for your chimney system.

 

Exterior Chimney. A chimney built on the outside of the house rather than up the middle of the house is more prone to wind- induced draft problems, since the chimney itself is more vulnerable to the elements. Wind draws heat away from the chimney, reducing the temperature of the smoke and gasses in the flue, thereby reducing draft. It is generally not practical to rebuild the chimney in the centre of the house. But if your chimney is an exterior one, it is even more critical that the rest of the system be correct - such as flue size, liner insulation, and chimney caps - to provide the best possible conditions in spite of the poor chimney location.

 

Pressure conditions in the House. Sometimes it is not the chimney that's to blame for a wind-induced smoking problem, but rather, the house. The chimney could be adequately tall, properly lined and capped, and the stove properly installed, and yet a wind-induced smoking problem could occur due to the construction of the house.

Example: Wind whipping around an unevenly-insulated home can actually draw air out of one side of the house, creating a depressurization problem inside the house (in much the same way as an exhaust fan draws air out). Depending on the location of the chimney, the house might actually pull air in through the chimney (and smoke with it) to make up for the air being sucked out by the wind.

The specific science of wind pressure is beyond the scope of this work. But the common element in wind-pressure problems is the wind-induced movement of air into and out of the house. Here's a thumbnail summary:

1. If wind factors create an area of low pressure in the room where the stove is located, then air (and smoke) may be drawn down the flue into the house to compensate.
2. If wind factors create an area of high pressure in the room where the stove is located, then the flow of smoke and gasses up the flue might actually be increased.
3. As a general rule, well-insulated homes are less prone to pressure changes inside the house from wind than poorly- insulated or unevenly-insulated homes, since less air is driven into or out of the house.
Without proper instruments and training, you won't be able to pinpoint this type of problem in your home. Your best bet is to tackle the other more obvious possibilities (above) first, such as chimney height, chimney caps, etc. If you continue to experience wind-related problems, take note of wind direction and intensity and whether or not the stove smokes. Consult your chimney professional or a venting specialist, and discuss the possibility that the house might be the culprit.

 

Smoking on Damp/Rainy Days

Some stoves seem to work just fine except when it is wet out. If this seems to be the case, pay close attention to the weather when you have smoking problems. It is easy to confuse wind-related problems with rain-related problems. If it does appear to be the wetness that does it, here are some possibilities:

 

Cold, Wet, Exterior Chimney. If you were stuck out in the rain, cold and wet, you probably wouldn't feel particularly energetic. Well, it's the same thing for chimney draft in chimneys built on the outside of the house. Wet masonry around the flue draws heat away from the smoke and gasses in the flue, reducing the draft, and making it much harder to heat the flue in the first place.
The solution, in most cases, is relatively simple: First, install a chimney cap on the flue if you don't already have one. A cap will keep most of the water out of the flue. Second, call your chimney professional and arrange to have a water repellent applied to the exterior brickwork, to prevent water from soaking into the chimney.

 

No Chimney Cap. Even if the chimney is built up the center of the house, so that most of it is protected from the rain, a chimney with no cap is like an open skylight: rain will run freely down the flue, drawing heat from the smoke and gasses in the flue and reducing draft. Get a cap. 

 

Warm Outside, Cold Inside. Sometimes on raw, rainy spring or fall days, it is actually warmer outside the house than inside. If this is the case, draft conditions, especially when starting the stove, will be adverse. You will probably need to spend some extra time priming the flue, and you may need to keep a fairly brisk fire going for a while, to warm the flue properly.

 

Smoke in Other Rooms

You operate the fireplace, and smoke enters in the basement below, or in some other room in the house. Sounds like a strange problem, doesn't it? But it is fairly common.
Some non-chimney-related possible causes are:

 

• Open windows, allowing smoke outside the house to come in. Sounds silly, but this happens more often than you might think.

• Fans or air exchange systems drawing smoke back into the house.

• Air currents in the house drawing smoke from the room where the fireplace is located.

 

If none of these seem to be the case, focus on the chimney-related possibilities:

Downdraft in Second Flue. Some chimneys contain more than one vertical passageway (flue). Often, a furnace or another fireplace or stove vents through the second flue. But if either (a) there is an unused second flue, or (b) the appliance it serves is not currently being used, then the unused flue, being cold, sometimes draws cold air down into the room where the chimney connection to the second flue is located.

Cold air sinking down this second flue can bring smoke from the fireplace with it. So the smoke is literally traveling up one flue and down the next. Check to see if the room where the smoke is found contains an opening into a second flue (or an appliance, like a stove or furnace connected to a second flue).

If you don't plan to use that flue or appliance, have a chimney professional seal the flue. This can be done either at the top of the chimney or where the unused appliance connects. Your chimney professional will advise you on the best way to do it.
If the second flue serves a fireplace that you sometimes use, have your chimney professional install a top-sealing damper on the second fireplace. This is a damper at the top of the fireplace flue, which you operate by means of a cable connected to a handle in the fireplace. It seals the second fireplace from the top, much more tightly than a standard throat damper (the cast-iron kind, installed just above the fireplace opening).

Of course, you have to open it when you use the second fireplace, but when you are using only the primary fireplace, keep it shut and no smoke will be drawn down to that room. And for those times when you want to use both fireplaces, a cold flue won't be a problem.

If the second flue serves a furnace, a wood stove, or some other appliance that you use, consult your chimney professional, as this can get sticky. Usually, the solution will be modifications to the chimney (such as adding height), re-lining with an insulated lining system, or some kind of chimney cap. A comprehensive look at the chimney structure by an expert will be necessary to make an accurate recommendation.

 

Breaks Between Adjacent Liners. Cross your fingers and hope this isn't the problem. If you have more than one flue in the chimney, you should have a liner in each flue. If there are breaks in the linings, smoke could be crossing over to one of the adjacent flues. A cross-flue problem like this can result in smoke leaking into the home through a chimney-connected appliance in another room.

If the flue liners are broken, or shift, creating gaps, and no wythe is present, smoke can cross over into an adjacent flue. If that flue is cold, the smoke might be drawn back into the house.
The solution is to re-line the chimney - not just to solve the cross-flue problem, but because a damaged flue liner is a serious fire hazard. If you use both flues, you need two new liners. Consult a chimney professional, and request a thorough check of the flue liners to determine if they are damaged and in need of replacement.

 

Chimney Cap Too Short. Chimney liners often extend a few inches above the top, or crown of the chimney. This is deliberate, as it helps keep water on the chimney crown from funneling down into the flues. But if you have a chimney cap (which you should) it is important to have enough space between the tops of the liner tiles and the cap. If the chimney cap is installed with too little space between the cap and the liners, smoke could back up into the house.

Check the space between your cap and the tops of the flue liners. Use binoculars if you can't tell, or ask your chimney professional to check it next time you have the chimney cleaned. Five inches or so is fine for a normal-sized cap, and often slightly less than that is adequate. But if the cap's only a couple inches above the tops of the flue liners, either (a) have the liners cut down, but not lower than your state and local codes require, or (b) install a taller cap.

And if the cap's unusually large – for example, if the chimney top is four feet wide and six feet long, and you have a full- sized cap on it, with the flues located under the center of the cap - then you might need a little extra space between the tops of the flue liners and the cap, since the cap could act like a baffle, retarding the flow of flue gasses.

If you think the cap is too low, but you are not sure, try removing it temporarily, and try the fireplace without it, before you start changing things. But a cap's important, so make necessary corrections and re-install it promptly.

 

Mechanical/Maintenance Problems with Wood Stoves

Although there are countless different models of wood stoves, there are relatively few basic types of stoves, and the mechanical problems they experience are similar. Your first step in caring for your stove is to read your owner's manual for specific information on your model of stove. Problems can include; damper malfunction, broken/stuck/loose handles, warped or broken parts, cracked or broken glass, worn or missing gaskets, malfunctioning catalytic combustors and poor performance.

 

Stove Damper Malfunction

Bypass Damper: Handle moves, damper doesn't. If you can move the handle of your by-pass damper, but the damper is stuck open or shut, there are three possibilities:

 

1. Disconnected or loose damper linkage. The handle is usually connected to a bar or lever that pushes up against the damper blade when you turn the handle. (The damper blade is the metal plate that opens and closes.) Sometimes there are several components leading from the handle to the damper blade, and one might have become disconnected, or loose enough that it isn't engaging the damper blade any more.

2. Broken damper linkage component. If someone has forced the handle of a stuck damper, a part may be broken.

3. Warped, broken, or misaligned damper blade. Especially under conditions of regular over-firing or rough use of the stove, the damper blade sometimes warps, breaks, or comes out of its proper seat, so the linkage no longer engages the blade.

In any of these cases, you have two choices: hire a chimney professional to examine and repair the stove, or try to do it yourself. Some damper linkages are easily accessible, and others are nearly impossible to get at. An exploded diagram of the stove will be especially useful. Ask at your local stove shop if you don't have one in your owner's manual.

 

Bypass damper: Handle is stuck. If the damper handle is stuck, don't force it! You could bend or break it, creating a much bigger problem. There are three basic causes of stuck bypass dampers:

 

1. Damper blade is warped. If the blade is warped from over-firing of the stove, it might become stuck in place. Sometimes this happens only when the stove is cold, or only when it is hot. This is due to the expansion of the metal: In one position or the other, (hot or cold) it might hit another component of the stove, or bend out of shape enough to prevent smooth operation.

2. Linkage is broken, bent, or improperly connected. Sometimes a damaged or improperly-connected component will jamb the linkage.

3. Improperly adjusted mechanism. Some dampers have adjustable devices such as snap-locks that hold the damper in the closed or open position to help prevent accidental movement of the damper, or tabs on the back of the damper blade that engage the damper linkage. If these are too tight, the damper could be stuck open or closed.

Again, the solution is to examine the damper and linkage, and repair/adjust/or replace as needed. A properly adjusted bypass damper should operate smoothly and easily.

 

Pipe damper: handle moves, blade doesn't. Most pipe dampers are connected to the handle by friction: the steel rod that passes through the stovepipe has a small ridge on it that pushes up against a corresponding indent in the damper blade. A spring on the handle outside of the stove pipe puts tension on the rod, keeping the rod engaged to the blade. (Take a look at it next time you have the stovepipe off for cleaning, and you will see that it is really quite simple.)

If the ridge on the rod or the indentation in the blade becomes worn, the damper blade may begin to spin freely on the rod, so that the damper handle no longer turns the blade properly.

First remove the section of stove pipe and clean the pipe and the damper, to verify that this is the problem. Sometimes you will find that the ridge has simply slipped out, and you can push it back where it belongs. If it is worn, measure the diameter of the stove pipe, and buy a replacement damper at your local stove shop.

 

Pipe damper: stuck. If the damper is stuck, chances are you have a buildup of creosote and soot in the pipe. Disconnect the section of stovepipe and clean it. If this happening it is usually worth having your chimney swept.

 

Door is too loose or too tight. Most door latches have adjustments on them. But if the door used to be okay and now seems too loose, first check the door gaskets. As gaskets become worn, the door will often feel loose. Since gaskets are the key to preventing air from leaking into the stove in the wrong place, replace them if they are worn, before you adjust the door latch.

If the door is too tight, first make sure it is properly in place and in good shape. Check the hinge pins for wear (replace them if they are worn), and carefully check to see if the door has become warped. A slightly- warped door may be okay, as long as you can properly gasket it and adjust the latch so that there are no air leaks. But if the door is badly warped or damaged, replace it.

Cracked/warped metal components. The metal plates on the inside of the stove are there to protect the outside of the stove from damage. If any of the burn plates becomes cracked or badly warped, replace it. It is a lot cheaper than replacing the whole stove down the road!

If an exterior part of the stove shows warping or cracks, you have a more serious condition. If you are up for a challenge and you have a good workshop, buy the replacement parts you need at your local stove shop, make sure you have an exploded diagram, and rebuild the stove. Be aware that it is never as easy as it looks! Those metal plates have been heated and cooled for a long time, and they won't always go back together again easily. You can also have an expert do the rebuild for you.

If the damage is severe, or if the stove is fairly old, maybe it is time to upgrade to a new, more efficient model. You will be amazed at the cleanliness, ease of use, and low wood consumption that a new stove will offer.

 

Cracked/broken fire bricks or refractory panels. Many stoves are lined with fire bricks or refractory panels. Minor cracks are generally not a problem, as long as the bricks stay together. But if they are badly cracked and start to fall apart, it is time to replace them.

 

Cracked or Broken Stove Glass

Under normal use, the stove glass will not crack or break. Glass breakage can be caused by:

 

• Severe over-firing of the stove.

• Impact (hitting the glass with a log, or slamming the door into a protruding log).

• Spilling cold liquids on hot glass.

• Improper glass installation.

In most stoves, the glass is held in place with steel clips or a cast-iron or steel frame around the glass. There is a gasket between the glass and the door, but not always between the glass and the clips or frame. If the frame is over-tightened or unevenly tightened, especially in doors that use clips, the glass could break from stress. Picture a piece of glass held in with small metal glass clips, two of which, opposite each other, are cranked in gorilla-tight. As the temperature of the stove and metal clips increases, the clips expand, exerting pressure on two points of the glass. This is an almost sure- fire way to break the glass, and it will usually crack from one clip to the other.

 

So if your stove glass breaks, before you take all the pieces out, take a look at where it broke. It may offer a clue to the cause. Obviously, you need to replace cracked or broken glass. If it has been a long time since you have re-gasketted around the glass, now's a good time to do that, too.

 

Worn or Missing Stove Gaskets

Gaskets around doors, ash pans, air intakes, or between metal panels of a wood stove are critical to proper stove performance. Leaky or missing gaskets let air in in the wrong place, fouling the burn and often severely reducing burn efficiency. Check the gaskets every year, and replace worn or missing ones. Write down the model of stove you have, measure how many feet of gasket you need, and go to your local stove shop to get the supplies. Generally, stove gaskets are cemented in place using gasket cement. You will need to remove the gasket and all the old cement before you install the new gasket. Use an old screwdriver or a wire wheel on a drill to completely remove the old cement.

 

Take Caution: wear protective clothing including gloves and eye protection.

When the surface is completely clean, apply a thin layer of new gasket cement, and push the gasket in place. If you are re-gasketing a door, close the door to make sure the gasket is pushed in properly. If it is bunched up, the door might not close, and you don't want to find that out when it is dry! Give the gasket a few hours to dry, and fire the stove. The cement cures with heat. If you don't want to tackle this job, ask your chimney professional to do it for you.

 

Poor Stove Performance

Sometimes it seems that the stove just isn't working as well as it used to. If there is no obvious problem, such as smoking, catalyst malfunction, etc., but it just doesn't seem to be doing the job it used to, consider these possibilities:

 

Worn/missing gaskets. Leaky stoves will often show a marked decrease in performance.

Chimney needs cleaning. If the venting system is getting blocked with soot and creosote, it will make a world of difference in terms of performance and safety.

Poor wood supply. If the wood you are burning is too green or wet, it will cause poor performance.

Changes in the house. Have you recently altered the house, by adding insulation, replacement windows, or new caulking? If you have made the house much less "leaky" recently, you may have a problem of depressurization.

 

Creosote

Creosote is a product of incomplete combustion: deposits of unburned, flammable tar vapors from wood smoke. Sometimes it is crusty or flaky in texture, but often sticky or hard, like slag. Creosote deposits are often hard to remove from chimneys, and pose a serious fire hazard. One of the great misunderstandings in the world of woodstoves is how creosote fits into the picture. Contrary to popular belief, creosote is not an inevitable product of wood burning. Creosote forms when wood is burned incompletely, and is an indication of improper use, poor installation, or a poor wood stove design. It is also extremely flammable, and is responsible for many chimney-related structural house fires each year. If you find a buildup of creosote in your stove pipe or chimney, have the chimney cleaned right away, and determine what's causing it. There are four basic possibilities:

 

1. Operating the stove at a too-low burn rate. Especially in air-tight stoves, if you damper the stove way down, for a long, low burn, you will create a smoky fire that emits lots of unburned tar vapors into the venting system. Since the temperature of the flue gasses will already be relatively low, these vapors will be particularly likely condense inside the pipe or chimney flue.

The solution is to keep the fire burning at a moderately-active rate. Go outside and check the flue. If lots of smoke is billowing from the chimney, you are burning it too low. Yes, this means you can't get as long a burn time from a load of wood, (unless you upgrade to a new, EPA-certified stove, which is designed to burn cleanly at a much lower burn rate) but you will actually get more heat from the same amount of wood, since creosote represents unburned fuel. You will also do your chimney and our environment a favor.

 

1. Using the wrong type of fuel. Burning green, wet, or excessively dry wood can cause creosote buildup.

2. Oversized flue or improper connection. If the chimney isn't quickly drawing the combustion products to the outdoors, due to an oversized flue, an excessively-long stove pipe, or too many elbows in the stove pipe - all of which tend to increase the amount of time the smoke stays in the venting system - then the smoke will tend to condense in the flue, forming creosote.

3. If your stove pipe is over eight feet long, or contains more than two elbows, consider re- installing the stove for a shorter run with fewer elbows.

4. Poor stove design. Before the new DEFRA approved stoves became available, "air- tight" wood stoves were considered the best type. Airflow into an air-tight stove can be closely controlled, in some cases to the point that the user can literally put out the fire by closing the air controls.

5. In essence, the problem with air- tight stoves is that, while they offer the convenience of a long, low burn, they are not designed to burn the fuel efficiently during periods of low burn. Lots of fuel is wasted in the form of smoke, which condenses in the stove pipe and chimney as creosote. 

6. The solution is the same as for Operating the stove at a too-low burn rate, above, although many older woodstove designs create a smoky burn no matter how you operate the stove.

Smells

There are several types of smell that could prevent you enjoying the use of your stove.

Creosote has a very strong, acrid smell, generally much worse in wet weather or in the summertime when the chimney is less effective in drawing the odor up the chimney. The first step is to have the chimney swept and stove pipe cleaned. But be aware that creosote can penetrate the surface of the chimney lining, so even after the chimney is cleaned, there may be some odor. During the summer, try disconnecting the stove pipe and plugging the thimble (the hole in the chimney) with a metal cap. Measure the diameter of the thimble and buy a plug for it at your local stove shop. Sometimes blocking the hole will prevent the odors from getting into the house. Also, if you don't have a chimney cap to keep the rain out of the flue, get one. Wet creosote smells a lot worse than dry creosote! A water-repellent treatment of the exterior brickwork might also help somewhat, by keeping the chimney structure dry. Talk to your chimney professional about it.
If there is a lingering smell after the stove has gone out, or during the summer months, first have your chimney checked to see if it needs cleaning. If the chimney has been swept recently, consider the following possibilities:

 

• No chimney cap. Dampness from rainwater in the chimney increases the odors emitted by soot deposits in the flue and ashes left in the stove. Solution: Get a rain cap.

• Soaking wet chimney. Just as a cap keeps water out of the inside of the chimney, a water repellent treatment keeps water from soaking into the outside of the chimney. And since a wet chimney smells more than a dry one, a water-repellent treatment might help. Ask your chimney professional about it.

• Wind-driven downdraft in the chimney. Ideally, a chimney will draw air out of the house even when you are not using the stove, pulling odors with it. But if the odors seem to coincide with windy days, reduced draft - especially in warm weather - coupled with wind pressure may be the culprits.

• Depressurized house. In some cases, air may be drawn into the house from the chimney, and odors along with it.

Burning stove paint odor. When your stove is new, or after you re-paint or polish it, there will be a period of burn-in, during which the stove will smoke and smell. Plan on burning the stove with the windows open for an hour or so after painting or polishing it. The procedure for "seasoning" new stoves is to burn several small fires before burning a long, hot fire. During these "seasoning" fires, most of the paint burn-in will take place. But the first few times you fire the stove high, you may get some residual burn-in odor. After five or six fires, it should stop.

 

Animals in the Chimney

If you hear animals in your chimney or if you smell something coming from your chimney that you suspect is from animals (dead or alive), call your chimney professional. Don't try to remove animals from the chimney yourself. Once your chimney professional has removed the animals, consider installing a chimney cowl with a birdguard.