Chapter 4: Solving Fireplace Problems

• Smoking Fireplaces
• Mechanical Troubles with Fireplaces
• Fireplace Odors
• Fireplace Leaks and Stains
• Animals in Fireplace Flues

The Troubleshooting Guide section on fireplaces, Page 77, contains a quick reference for fireplace problems and solutions. If you have a specific problem you want to address, you might start there, but you will find much more detail in this section.

It is one of the most valued features in our homes. And all too often, the fireplace is labeled "non-working" and sits unused, because the homeowner doesn't know what to do about a smoking problem. Here I will show how most smoking problems can be handled relatively easily, with little or no expense. We'll cover:

• Smoky Startups
• Smoky Endings
• Constant Smoking
• Smoking on Windy Days
• Smoking on Damp/Rainy Days
• Smoking in Other Rooms

Here's a trick for monitoring smoky fireplaces: If you can't see the smoke spilling from the fireplace, shine a flashlight across the fireplace opening. The light reflecting off the smoke particles will make it easy to see.

The most common smoking troubles occur when the fire is first lit. If your fireplace smokes only during startup, but is okay after that, here are some possibilities:

Fireplace Dampers. The purpose of the fireplace damper is to prevent heat loss when the fireplace is not being used. Don't forget to open it before you start a fire. But when the fire is completely out (usually sometime the following day), don't forget to close it. An open damper is like an open window, allowing huge amounts of heated air to escape.

When you are ready to light a fire, open the damper completely. Some people try to operate the fireplace with the damper closed partway, in an effort to get more heat into the room. But you won't gain much, if anything, by closing it part way, and you might gain a house full of smoke! No matter how you operate it, a standard open fireplace is not an efficient heater. Its purpose is atmosphere and entertainment. So forget about efficiency. Open that damper, and leave it open until the fire is out.

Cold Flue. The flue will be cold when you first open the damper. This is especially true in fireplace chimneys built on the outside of the house, rather than up the middle of the house. A tall column of cold air in the flue will tend to sink, causing air to move down the chimney and into the house. So if you open the damper and feel cold air coming down the chimney, don't light the fire! If you do, smoke might be forced back into the house.

What you need is a tall column of warm air in the chimney. So first, prime the flue.

HOW TO PRIME THE FLUE: Roll up a piece of newspaper, light one end, and hold it way up in the damper opening. You might need to burn two rolls of paper. In a minute or so, you will 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 you have a severe cold-chimney problem, and the newspaper trick doesn't seem to be working, try leaving the damper open for half an hour or so, allowing heated room air to gradually reverse the flow. Yeah, that's a lot of cold air coming down. But remember, this thing is for entertainment, not heat. Right? You can use the half hour to chill a nice bottle of champagne...

Blockages. Sometimes a smoking problem is caused by a partial or complete blockage of the flue. Animal nests, leaves and debris, or internal collapse of chimney 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.

Some fireplaces work just fine as long as you keep a rip-roaring fire going. But let it burn low, and it starts to smoke. (You might find that this type of fireplace is also smoky at startup, as discussed above.) The solution is to keep it burning high until spring, when you can open the windows... Just kidding. But seriously now, read on if your fireplace is okay during high-fire, but smokes as it burns low.

Sometimes this is due to a design problem that can be easily solved. In other cases, it is more serious, and difficult to remedy.

The exterior chimney: cold flue by design. If a masonry chimney is built on the outside of the house, and not up the middle of the house, the chimney structure, and therefore the flue, will sometimes cool quickly as the fire burns low. Especially on windy or rainy days, when weather conditions draw heat from the masonry structure more rapidly, this cooling can create a reverse-draft problem: Cold air sinks, and the smoke sinks with it. Right into the living room.

It is easier for masons to build chimneys on the outside of the house, after the house structure is mostly completed. But venting specialists recommend building masonry chimneys up the inside of the house structure, to avoid cold flue problems.

Sometimes you can alleviate this type of problem with a good set of glass fireplace doors. As the fire burns low, close the doors to keep the smoke from entering the house. This is the easiest and cheapest possible solution, and the one I'd recommend first, before you spend money on structural changes.

A note about glass doors: Glass doors are useful, even for non- problematic fireplaces, since you can close the doors before you go to bed and prevent heat loss up the flue. Remember, you can't close the damper until the fire is totally out, usually a day or more later. And an open damper is like an open window.

Other Design Problems. There are several possible design problems that could cause smoky endings. Some of these are easy to check. Others require the skills of a chimney professional. Here are some to look for:

Inadequate Chimney Height. This one is fairly easy to check. First, check to see if the chimney meets the basic height rule.

CHIMNEY HEIGHT RULE: The chimney should be at least 3 feet higher than the highest point where it passes through the roofline, and at least 2 feet higher than any part of the house within ten feet of it.

In other words, all chimneys must extend at least three feet above the roof. And to find out if yours needs to be taller than three feet, measure horizontally from the side of the chimney, ten feet out on all sides. If you hit the roof, or an addition, or any other structure, then the chimney must be at least two feet higher than your measuring tape. If the chimney is any shorter, you are likely to experience draft problems, especially (but not only) when it is windy.

There are some reasons for building a chimney higher than the minimum according to the rule. For example, if the chimney is built down near the gutter line, and the house itself is much higher than the top of the chimney, you might need a higher chimney. This is due to the stack effect of the house.

Stack Effect: movement of air in the house created by the difference in pressure between air in the house and air outside.

Here is how it works: if lots of heated air is exiting the house at the top (from a leaky or poorly insulated roof, open windows upstairs, etc.) then the house acts like a chimney, or stack, drawing air up from downstairs to replace the heated air that's exiting. If the stack effect of the house is stronger than the chimney draft, you have a problem, since the house will draw air from the chimney, too, causing smoke and exhaust spillage.

Measuring this gets pretty complicated, so if you suspect a stack effect problem, read through the other possibilities first (especially Depressurized House, below), then consult your chimney professional for advice if you still think stack effect's the culprit.

Over-sized Flue. Your flue liner might be too large for the fireplace. Some contractors seem to think "bigger is better." But if you have too large a flue, then the amount of heat produced by a low fire might not be enough to "drive the draft" – that is, to keep that big flue warm enough. If cold air starts to rush down... You get the picture.

Most masonry fireplace flues are lined with 8" x 12" terra-cotta tiles. But this is a nominal dimension, and the actual inside dimension is usually closer to 6.5" x 10.5". If you have a larger-than-normal fireplace, you might need a larger flue.

Calculating the correct flue liner size is pretty complicated. But as a rough-and- ready guess, if you answer yes to all of these questions, an oversized flue might be the problem.

1. Is the fireplace opening pretty close to 36" wide x 28" tall (or smaller)?
2. Is the flue larger than an 8" x 12" nominal liner"?
3. Is the house fairly open, or drafty, rather than being tightly insulated? (If it is very tight, consider "Depressurized House", below, first.)
4. Is the chimney built up the inside of the house? (If it is on the outside, see The Exterior Chimney, page 27, 61.)

If so, the next step is to hire a chimney professional to examine the entire system. If your chimney professional determines that the flue really is too large, the solution is to re-line the flue.

Depressurized House. Especially in newer, tighter homes, or homes with mechanical air exchange systems, depressurization of the inside of the home can be a problem. A fireplace chimney draws a huge volume of air out of the house. If either (a) something else is also drawing air out of the house, like an open window upstairs, an exhaust fan, or an air exchange system, or (b) the house is so tightly insulated that not enough air is leaking back inside to make up for the air exiting through the fireplace flue, then there is the possibility that the house will draw air from the chimney, and smoke along with it. This is even more likely as the fire burns down, emitting less heat to keep the flue warm.

TEST FOR DEPRESSURIZATION IN WELL-INSULATED HOMES: First, make sure there are no exhaust fans, air exchange systems, etc. in operation, and close any open windows upstairs. Crack open a window, in the same room with the fireplace. (NOT in another room, and definitely not upstairs!) This will allow outside air to enter the room, equalizing the pressure. If you find that the smoking problem stops, then depressurization is the culprit.

Note: This test is best done on a calm day, since wind pressure against the house adds another factor. Depending on wind speed and direction, air might actually be drawn out of the cracked window, giving an incorrect result.

Since an open window isn't particularly desirable, consider an outside air duct. An outside air duct, as the name implies, is an air duct (usually a metal pipe) that allows outside air to enter the home, relieving the depressurization problem. Talk to a chimney professional about installing one.

Improper air space around the liner. This is a tough one. If you have a brick or stone chimney, chances are you have a terra-cotta (clay) liner inside the masonry work. There is supposed to be an air space between the liner and the brick/stone work. Sometimes, this air space is too large, especially in large, decorative chimneys that hold only one or two flues. A small air space is a terrific insulator. But a large air space can actually cause heat to be drawn away from the liner, causing lower flue temperatures, and consequently, draft problems.

If your chimney is quite large, and especially if it is built on the outside of the house rather than up the middle of the house, this could be a factor in a smoking problem. But consult a chimney professional on this one, as some remedies (such as a new, insulated liner) could prove costly, and less drastic remedies might suffice.

Note:In some regions, the space between the liner and the casing might be filled deliberately. An example is in California, where chimneys are reinforced with steel bars, and the space is required to be filled, in an effort to help the chimney withstand earthquakes. The technical ramifications of this relatively new construction practice are beyond the scope of this work. And in most regions, the air space is considered an integral part of good chimney design, provided it does not exceed the recommended size.

If the fireplace always smokes, the problem might be:

Blockage. Sometimes, a smoking problem is caused by a partial or complete blockage of the flue. See page 27 for details.

Depressurized House. Although this problem sometimes only shows up when the fire is burning low, for some super-tight houses it is a constant problem. This is the first possibility to explore if you have a tightly- insulated house, an air exchange system, or exhaust fans in operation. If there is not enough air available in the house to allow the fireplace to draw, it will smoke. See the explanation and solution in the Smoky Endings section, Page 29.

Smoke Chamber is too small. The triangular cavity (above the damper) that funnels the smoke up into the flue liner is called the smoke chamber. While an oversized smoke chamber can lead to difficulty in getting the draft going, if the smoke chamber is too small, smoke sometimes curls out at the top of the fireplace opening and spills into the room.

When the fire is out, open the damper and shine a flashlight up into the smoke chamber.

The side walls of the smoke chamber shouldn't be more than 45 degrees from vertical. Usually, the smoke chamber is about three feet high. If yours is closer to 18 inches, or shorter, it could be the culprit. A smoke guard or fireplace doors might solve the problem.

Smoke guard.

A smoke guard is a piece of non-combustible material (usually steel) placed over the top of the fireplace opening, to lower the opening.

Before you buy one, do this: Take a piece of aluminum foil a little wider than the fireplace opening, and fold it in half width-wise, to make it sturdier. When the fire is going, tape it over the top of the opening, covering a few inches of the opening. (Go easy on the tape! You will want to adjust it.) Monitor the fireplace as the fire burns. If it spills smoke, lower the foil. If it doesn't, raise it. Adjust it until you find out (a) if it works at all, and (b) how much of the opening you need to cover in order to solve the problem.

If your foil smoke-guard works, go out and buy a smoke guard at least as wide as you need.

Fireplace doors.

Fireplace doors are generally constructed of tempered glass panels in a metal frame. The frame usually covers a couple of inches of the fireplace opening, so fireplace doors act something like a smoke guard, lowering the effective opening of the fireplace.

And, if the fireplace starts to smoke, you can close the doors. Fireplace doors also save heat, since you can close them before you go to bed, preventing heat loss up the flue. (Remember, you can't close the damper until the fire is completely out, often a day or more later.)

Flue is Too Small. If the flue is too small, it might not be able to handle to volume of airflow needed to draw the smoke up and out.

Most masonry fireplace flues are lined with 8" x 12" terra-cotta tiles. But this is a nominal dimension, and the actual inside dimension is usually closer to 6.5" x 10.5".

Calculating the correct flue liner size is pretty complicated. But as a rough-and-ready guess, if you answer yes to all of these questions, an undersized flue might be the problem.

• Is the fireplace opening pretty close to 36" wide x 28" tall (or larger)?
• Is the flue liner smaller than an 8" x 12" nominal liner?
• Is the house fairly open, or drafty, rather than being tightly insulated? (If it is very tight, consider Depressurized House, page 29, first.)
• Is the chimney built up the inside of the house? (If it is on the outside, see The Exterior Chimney, page 27, 61.)

If so, the next step is to hire a chimney professional to examine the entire system. If your chimney professional determines that the flue really is too small, the solution is a smoke guard or fireplace doors (see page 30). These two devices will reduce the opening size of your fireplace, changing the ratio of the opening size to the flue size, improving the fireplace's ability to draw all the smoke up and out.

Damper is Too Low. Similar to the small smoke chamber problem is the misplaced damper. Normally, there is some room above the top of the fireplace opening for smoke to gather before it moves through the damper and into the smoke chamber. But if the damper is installed right at the top of the fireplace opening, smoke sometimes spills into the room.

This is especially problematic if the damper opening is particularly narrow, or if the damper is installed at a steep angle, acting like a baffle.

A "baffle" is anything that slows or re-directs the flow of smoke and gasses.

The solution to a misplaced damper is either (a) to remove and replace the damper, often a costly and involved proposition, or (b) to install a smoke guard or fireplace doors (see page 30). Smoke guards and fireplace doors work by lowering the top of the fireplace opening, adding extra space for the smoke as it collects prior to passing through the damper.

Chimney is Too Short. Wind patterns around a house create pressure zones against the roof. Wind-driven pressure zones are a complicated science, but basically, if the chimney is not tall enough, a pressure zone created by wind will engulf the chimney top, forcing wind-driven smoke down the flue and into the house.

This is why current building standards require a minimum chimney height of three feet above the roof penetration, and two feet higher than anything within ten feet of the chimney. If your chimney doesn't meet this standard, have a professional add height to it. (See page 28 for details on the height rule.)

Sometimes, although the chimney is tall enough compared to the roof, its overall height isn't adequate to overcome a driving wind. Especially for short chimneys in one-story homes, adding height above the required minimum is a good idea if wind is a problem. Ask your chimney professional for advice.

No Chimney Cap. A chimney is an open cavity leading into your home. As such, all chimneys should have caps. A good chimney cap, constructed of stainless steel, copper, masonry, stone, etc, will not only prevent rain and snow from entering the flue, but will also help with certain wind- driven draft problems. The science of pressure differentials is fodder for physicists. Suffice it to say that a good cap, properly installed, helps keep the wind from blowing down the chimney.

This can be a real nuisance. Here is what to look for:

Cold, Wet Flue. Wet chimney flues are much harder to heat than dry chimney flues. This is because it takes an enormous amount of heat to convert water to steam. The water absorbs so much heat that the flue doesn't warm up effectively. The tall column of cold air in the flue wants to sink, drawing smoke into the house.

Try pre-heating, or priming the flue. (See page 26 for details and instructions.) Sometimes, by pre-heating the flue with the priming technique, you will overcome the problem.

Other things that will help include a good chimney cap to help keep water out of the flue, and a water-repellent treatment for the exterior masonry work.

A word about water repellents: Don't use a foundation or masonry sealer on chimneys. Burning wood creates moisture, and the chimney needs to "breathe," to allow the moisture to escape. Sealers lock this moisture in, causing gradual damage to the structure. Instead, use a vapor-permeable water repellent designed for use on masonry surfaces. Ask your chimney professional for a quote.

Chimney is Too Short. Especially on damp, wet days, when the temperature and pressure differential between the inside of the chimney and the outside isn't ideal for chimney draft, it is important for the chimney to be tall enough. You need a tallcolumn of warm air to drive the draft. (See page 28 for details on the height rule.)

Current building standards require a minimum chimney height of three feet above the roof penetration, and two feet higher than anything within ten feet of the chimney. If your chimney doesn't meet this standard, have a professional add height to it.

Sometimes even when the chimney is tall enough to meet the building standard, its overall height isn't adequate. Especially for short chimneys in one-story homes, extra height above the required minimum is a good idea. But talk to your chimney professional for advice before you spend money on adding height.

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).

Note: Sometimes old openings into chimney flues are covered with a metal "pie plate" on the wall. These are likely spots for smoke to enter, as "pie plate" covers are not air tight.

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.

The best way to build a masonry chimney is to separate each flue with a solid brick partition (called a wythe). But in some regions, a wythe is not required by code. And even in areas where it is required, some chimneys are not actually built with a wythe between the flues.

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.

Sometimes it is the little problems that make a fireplace seem unusable. Here we will cover some common mechanical difficulties, and how to solve them.

• Stuck or Non-Functional Dampers
• Fireplace Door Difficulties

Corrosion and debris are the most common causes of stuck dampers.

A good first step is to have the fireplace professionally cleaned. Your chimney professional will sweep the flue and remove the soot and debris that is piled up around the damper. At the same time, he/she can lubricate the moving parts and make adjustments, or recommend a new damper if yours is damaged beyond repair. If it has been a year or more since you have had the flue cleaned, have it done, anyway, for fire safety.

For the do-it-yourselfers, here are some hints for fixing dampers. But this doesn't take the place of a professional chimney cleaning.

Fixing Throat Dampers. If your damper is a throat damper, the kind located just above the fireplace opening, it is operated either by a handle inside the fireplace, or by a small knob on the outside, somewhere between the mantel and the opening.

Using a flashlight, take a look at the moving parts. If anything looks warped, rotten, or broken, call your chimney professional for a quote on a replacement damper. If the parts look rusty or corroded, first try oiling them. A spray penetrating oil works well. Put some newspaper down in the fireplace to catch run-off, and don't get any oil on the brickwork.

Take a look at how the handle assembly works. Some are simply a notched handle that pushes the damper blade up. (The damper blade is the plate, the thing that actually opens and closes.)

Others (among the external-knob type) have a worm-gear on a shaft. When you turn the knob, the shaft turns the worm gear. A ring moves along the worm gear, and pushes a lever connected to the damper blade. It sounds complicated, but take a look, and you will see it is pretty simple.

A third type incorporates a handle and a counter-weight. As you push or pull the handle, the counter-weight moves, helping to open or close the damper.

Yours might also be a variation on these basic types. Try pushing (gently!) against the damper blade. See if the damper blade's stuck, or if the handle mechanism seems to be the culprit.

You might find that there is a buildup of sand, soot, and debris behind the damper that is preventing the blade from moving. If so, have the chimney cleaned.

Also, check along the bottom edge of the damper blade. Sometimes there are metal tabs or notches designed to fit into slots or holes in the housing. If the blade isn't set in place properly, that could be your problem.Sometimes it is necessary to disassemble the handle mechanism to get the blade back where it goes.

It is probably wise to call a professional at this point, or you may end up with a pile of parts and no idea how to put them back – especially if you have the external-knob style of damper. If you decide to try it, be careful! Don't drop any pieces. Cast-iron parts break easily, and you could hurt yourself, too.

Fixing top-sealing dampers. Adjusting a top- sealing damper requires getting up on the roof, a job best left to a chimney professional. Although top-sealing dampers tend to be relatively trouble-free, sometimes the cables need to be replaced or adjusted, or debris interferes with the moving parts.

If you think the damper is frozen shut (during or after an ice storm), check with the operating instructions or the installer. Sometimes there is a feature built into the damper that allows you to tug sharply on the cord, engaging a lever-type device on the damper that breaks the ice seal.

A good set of fireplace doors is a highly- recommended accessory, for saving heat and optimizing your enjoyment of the fireplace. But if the doors are damaged, improperly installed, or out of adjustment, they can be frustrating. Your chimney professional can fix most fireplace door problems.

But if you want to give it a try, here are some things to check.

Adjusting fireplace doors. If the doors don't open and close smoothly, first check to see if there is an adjustment. Often, where the doors attach to the frame there is an adjustment that allows the top and/or the bottom of each door to be moved left or right, correcting a binding or poorly- operating door.

If there is no adjustment, or if there is not enough adjustment to completely solve the problem, the door frame may be improperly installed. If it is crooked, loose, or uneven, it could force the doors "out of square," making them operate poorly.

Most doors attach at the top by means of a clamp assembly. A thumb-screw tightens the clamp assembly to the lintel bar, the piece of angle-iron that holds the bricks up at the top of the fireplace opening. At the bottom, the doors are usually bolted into the inner hearth. Take a look, and you will see how this works.

If the doors seem crooked or loose, and if you are brave, you can try adjusting the clamps. But have somebody else on hand to steady the door before you adjust anything, or the door could fall.

If the door frame itself is badly worn or warped, you will probably need a new set of doors.

Broken glass. Fireplace doors incorporate tempered glass that's designed to withstand heat – to a point. With better-quality doors, you can operate the fireplace with the doors open or closed. But some things can cause breakage.

You can save yourself from the rather startling experience of a exploding glass door by knowing a little bit about different types of doors an their appropriate use.

The easiest way to break glass doors is to over-fire the fireplace. Burning pizza boxes, big stacks of dry pine, etc. (things that also pose a serious fire hazard) could cause thermal shock breakage. Tempered glass can withstand very high temperatures if heated and cooled slowly. But a rapid change in temperature causes thermal shock, rapid expansion or contraction, often resulting in damage.

If you plunge a hot drinking glass into a sink full of cold water, the glass will break. That's thermal shock. And it can happen to fireplace doors, too.

As you might assume, thin glass doors are much more susceptible to breakage than thick ones. Better-quality doors use glass roughly 3/16" thick or thicker. Some come with a lifetime warranty against breakage.

Keep the fire several inches back from the doors, to reduce thermal shock. At least six inches between the inside of the doors and the fireplace grate is a good idea.

Don't try this at home: As a demonstration, some sales reps will smack a door on the showroom floor with a poker. It shows that thick tempered glass doors can withstand a lot of abuse. But obviously, if you hit the glass hard enough, it will break. So don't slam logs or tools into your doors, especially if the glass is the thinner kind.

Finally, if you have a two-sided fireplace (one with two openings), and you have glass doors, you must operate the fireplace with both doors open or with both doors closed. (And if the doors aren't good quality, keep both open!) Operating a two-sided fireplace with one set open and one closed causes extreme heat against the closed set, which could break the glass.

Warped or damaged screens. Sliding-mesh screens will eventually warp from heat, but can be replaced easily and inexpensively. Measure the height and width of the actual mesh (not the fireplace opening), and buy a replacement mesh from your local stove shop. If you are not sure how to remove the old mesh and install the new one, have your chimney professional do the job for you.

If you have a standing or gate-style screen and the frame is okay, but the screen is in bad shape, you can probably have the screen replaced, also, but in some cases it is less expensive to buy a new screen. Ask at your local stove shop for more information.

Missing, damaged, or inoperable ash pit door. Some masonry fireplaces have an ash pit door, a small door in the bottom of the firebox that leads to an ash pit under the fireplace. (See page 18, Cleaning Up for details on ash pits.) If the door is missing or damaged, replace it. Usually the door simply lifts out. Bring what's left of the old one (or very accurate measurements of the hole size) to your local stove shop and buy another one.

If the door is there, but rusted shut, try some penetrating oil first. You might want to take the door out and fix it in your workshop.

If you notice odors while you are using the fireplace, then you almost certainly have a smoking problem. See page 26 for details on identifying and correcting fireplace smoking problems.

As a general rule, in any case of fireplace odors, a chimney cleaning is in order if you haven't had it done recently (and certainly, if it has been over a year and you use the fireplace). A buildup of soot in the chimney will increase odor problems significantly.

If you have had the chimney cleaned and you still have an odor problem, here are some possible causes and solutions.

Open damper. If the damper is open and you are not using the fireplace, close it, to minimize air movement from the chimney into the house.

No chimney cap. A chimney cap helps prevent rainwater and snow from entering the flue. And since moisture increases odors, a drier chimney will tend to emit less odor. If you don't have one, ask your chimney professional about having one installed.

Soaking wet chimney. If it has been rainy or wet lately, a masonry chimney might be soaked with water. Especially if the chimney is built up the outside of the house, water penetration can be a problem. Water draws heat from the flue, reducing the natural draft that helps draw odors up through the chimney and out. Sometimes having a water-repellent treatment (available through your chimney professional) will help. See page 33 for important advice concerning water repellents.

Short chimney. If the chimney is too short, you will not only be likely to experience smoking problems when using the fireplace, but you will also be more likely to experience odor problems. Chimneys that are too short tend to have inadequate draft to draw smoke and odors up and out. See page 28 for details on correct chimney height. The solution is to add height.

A note on odor problems. Poor chimney draft, and the resulting problem of odors entering the home, can also be caused by depressurization of tightly-insulated homes. If the house is so tight that there is not enough air available to replace the air leaving the house up through the chimney, then the chimney draft can actually reverse, causing air to be drawn into the house from the chimney, and odors with it. See page 29 for details on the problem of depressurization.

Here we will discuss leaks and stains found in and around a fireplace.

Water leaking into the fireplace. Water should not leak into your fireplace. If it does, first be sure you have a chimney cap to keep water from running freely down the flue. (See page 10 for information about caps.)

If you have a cap, the problem might be more serious. Cracks or holes in the crown (the very top) or in other areas could be allowing water to leak into the chimney. If so, masonry repairs are in order, for safety and to fix the water leak.

It is also possible that pooling water might be soaking through the structure and leaking in. A water repellent treatment will help if this is the case. (See page 33 for details.)

In any case, it is wise to consult a chimney professional, as water entering the chimney will gradually damage the chimney structure, and could indicate a serious problem.

White stains inside the fireplace. Efflorescence, also called leeching, is deposits of salts on the masonry surface. It is caused by water soaking through the joints, dissolving the salts, and re-depositing them on the surface. Efflorescence is an early indicator of water damage, often seen inside the fireplace due to water pooling above the damper and soaking through. Fortunately, you can usually wash these stains off fairly easily.

The methods listed above for reducing water entry – a chimney cap, repairs to cracks or holes, and a water-repellent treatment – will reduce or eliminate efflorescence.

Black stains above or to the sides of the fireplace opening. Smoke stains around the fireplace opening are an indication of either (a) improper use of the fireplace, or (b) a smoking problem. First, correct the problem. Read about using your fireplace in Part 3 (starting on page 18), and make needed repairs or changes to solve smoking problems. (See Smoking Fireplaces, page 26.) Then, to clean stains on masonry surfaces, purchase a masonry cleaner at your local stove shop. This will be a liquid cleaner, usually in a pump-spray bottle.

Be aware that you will need to clean the entire surface, and not just the stained part, since cleaning the masonry surface will lighten it a bit. And don't expect to remove every trace of the stain. Mortar joints are porous, and draw stains in. It is practically impossible to completely remove a stain. But you will be pleasantly surprised at the difference a good cleaning will make.

If the stains are on non-masonry surfaces, such as painted walls, metal components of factory-built fireplaces, or wood mantels, try a mild household cleaner first. If it doesn't work, talk to a professional cleaning company or a smoke restoration company.

A special case. Sometimes smoke stains are caused by leaky gaskets around the frame of a fireplace door. Most doors incorporate a fiberglass gasket between the door frame and the masonry surface. If you have a set of doors and see "finger" shaped smoke stains around the outer edges of the frame, then you need to replace or fix this gasket. Since this generally requires removing and re-installing the doors, you might want to hire a chimney professional to do the job.

Raccoons, squirrels, birds, bats, and other animals can get into chimneys if there is no cap to keep them out. These animals can bring fleas and ticks into your home, as well as rabies, worms, and other diseases. So animals in the chimney pose a serious health risk. If you see or hear animals in the chimney, call your chimney professional and have them removed. Then have a chimney cap with a screen mesh installed on the chimney to prevent future infestation.

It is also a good habit to keep the fireplace damper (or glass doors) closed, to prevent the animals from getting into the house.