How Chimneys Work

What’s inside a chimney? How does it work? What parts can a homeowner check? Here we will discuss chimney basics, including:

One thing I have noticed over the years is that there are a lot of people who have fireplaces or stoves and would like to have a fire now and then, but never do because they think there is something wrong with the fireplace, stove, or chimney.

Chimneys are not particularly complicated, but most people don’t really understand how they work. Knowing the basics will make sense of the whole process of building a successful and safe fire and how to avoid common chimney-related problems.

In later sections we will talk about the appliances ­ stoves and fireplaces ­ and what you need to know about them.

Types of Chimneys

Masonry Chimneys:
What we usually picture when we think about chimneys is a masonry chimney: one constructed of brick, concrete blocks, or stone. But current building technology includes another major category, the factory-built chimney.

Factory-Built Chimneys:
Builders and remodelers can now choose from a wide variety of chimneys constructed of metal and other materials. These chimneys are manufactured in a factory and assembled at the site. Among the more popular types of factory-built chimneys are:

  • Double-wall, mass-insulated chimneys. Two layers of metal, generally stainless steel, with an insulative material between the layers of metal. Picture a pipe inside a larger pipe, with the space between the two packed with insulation.
  • Air-cooled chimneys. Two or more layers of metal with air in between, constructed so that the air circulates between the layers, dissipating the heat.
  • Air-insulated chimneys. Similar to the air-cooled design, except it is constructed for minimal movement of air between the layers, so the air acts as an insulator instead of drawing heat away.
  • Combinations. Chimneys which incorporate a combination of mass-insulation, air-cooling and/or air insulating designs.

With so many types of chimneys to choose from, the question arises…

What type of chimney is the best?
There are advantages and limitations to each kind: Masonry chimneys incorporate traditional beauty that many homeowners want. Factory-built chimneys offer a non-masonry option that often proves easier to install, at a lower price. Some types of chimneys are designed only for appliances that burn certain fuels.

Determining the best type of chimney for you requires a complete picture of the specific appliances (fireplaces, wood stoves, furnaces, etc.) that the chimney must serve, and the specific venting requirements for those appliances.

For example, factory-built fireplaces often require specific types of factory-built chimneys, while most wood stoves can be connected to either a masonry chimney or certain types of factory-built chimneys.

If you plan to have a new chimney installed, first find out what type of chimney you need for your appliance. Check the owner’s manual for wood stoves or factory-built fireplaces. Chimney requirements should be spelled out pretty clearly.

If you plan to install a new (or used) appliance into an existing chimney, you need to do the same thing. It could be disastrous, for example, to connect a wood stove into a chimney that is designed only for a certain type of fireplace. Don’t assume that you have the right type of chimney. Find out for certain.

Anatomy of a Chimney

A chimney, simply put, is a vertical tube designed to draw combustion products (smoke and gasses) from an appliance like a wood stove or fireplace to the atmosphere outside the house. Here are the basic parts:

Inside a chimney you’ll find one or more vertical passageways called flues. Ideally, each appliance connected to the chimney (such as each fireplace, each furnace, each wood stove) has its own, separate flue. More than one flue might be contained in one masonry chimney. So if you have a furnace and a fireplace connected to the same chimney, there should be at least two vertical passageways up the inside of the chimney.

Metal factory-built chimneys, of course, contain only one passageway for venting combustion products, the inside of the pipe.

Flue liners:
In a modern masonry chimney, the inner wall of the flue is lined with some type of material, for safety, ease of cleaning, and improved performance. Among the most common types of liners are:

  • Terra-cotta. Baked clay liners, also called terra-cotta or tile liners, are generally about 5/8″ thick, and look like two-foot long square, rectangular, or round tubes. They are cemented end-to-end up the inside of the flue to form a continuous, smooth lining.
  • Other modular liners. Terra cotta is not the only material used to make modular liner tubes. Some are composed of refractory cement, volcanic pumice, or a combination of fireproof materials.
  • Stainless Steel. Especially useful in re-lining existing chimneys (But used in new construction, as well), stainless steel liner systems incorporate a metal tube, rigid or flexible, with some type of insulation around it. The metal tube provides a continuous, even lining, and the insulation forms an additional layer of protection and helps keep the flue warm.
  • Aluminum. Some installations of gas-fired equipment allow for the use of lower-cost aluminum liner systems.
  • Cast-in-place. Cast-in-place liners are, in essence, a thick layer of a highly durable, insulative, cement-type material applied to the walls of the flue.
    • One method (but not the only one) for installing a cast-in-place lining involves inserting a removable rubber tube the full length of the flue and pumping the liner material in. The tube is later removed, leaving a smooth-walled, cast-in-place flue liner.
  • Note: For a metal factory-built chimney, the inner wall of the chimney serves the purpose of a chimney liner.

Which is the Best Type of Liner?
This depends on many factors, including the type of appliance, the type of chimney, and its intended use ­ not to mention, who’s answering the question! If you are planning to have a new chimney built, or considering having your chimney re-lined, get as much information as possible about the appliances you will be using on that chimney. Check the owner’s manual to see if there are specific recommendations for or against certain types of chimneys or liners. Talk to the experts at your local stove shop, and talk to your chimney professional.

Don’t assume that any old liner is fine, or that the brick mason knows what type of liner is best. I do not mean to be critical of masons ­ their work is certainly important, and a good mason is a true artist. But with new woodburning technology has come the need for new types of liners; and if you don’t ask the people on the front lines, the ones who deal with the issue of selling theses appliances and making happy customers, you might end up with a chimney liner that is totally inadequate for your needs ­ even though it might be a doggoned well-built one!

Current construction and safety standards require that all chimneys be lined. So if you think your chimney is unlined, or you are not sure, have your chimney checked by a chimney professional, and ask him/her what types of liners are appropriate for installation in your chimney.

Chimney Crown:
The top of a masonry chimney is called the crown. It should be gently sloped toward the edge, causing rainwater to run off. The flue liners should extend above the crown at least two inches (maybe more, depending on the local building code), so you might be able to see the tops of the liners from the ground.

Cleanout door:
At the base of each flue you should find a small, metal cleanout door. When your chimney professional cleans the flue, the soot and debris will be removed through this cleanout access. The exception is a fireplace, which needs no door, since the soot is cleaned out right at the fireplace opening. If you find a door in the cellar centered below the fireplace, it is probably an ash pit door. We will talk about that in the section on fireplaces.

How Chimneys Work

The purpose of a chimney is to take the combustion products (smoke and gasses) from the appliance to the atmosphere outside your home, and at the same time, to draw air for combustion into the appliance. This movement of combustion air and exhaust is called draft.

In essence, it is the difference in pressure between the air/gasses inside the chimney flue and the outside air that creates this movement. Warmer, lighter gasses in the flue tend to move upward.

To keep the pressure conditions favorable, we need a tall column of warm air inside the chimney, and cooler air outside. The warm air will tend to rise, drawing the exhaust from the appliance out. As air exits the chimney, fresh air for combustion is drawn into the appliance.

Factors affecting draft. Since draft is a measure of pressure, chimney draft is affected by pressure conditions in the house. Several factors come into play:

  1. Adequate air. First, there must be adequate air movement into the house to make up for the air exiting through the chimney. If the house is very tightly insulated, the volume of air drawn up the flue will exceed the volume of air entering the house, and the house will gradually become depressurized. With lower pressure in the house than outside, there will be a tendency for air to be drawn into the house from all available openings ­ including down the chimney.
  2. Air movement in the house. Second, air movement in the house must not interfere with the chimney. Picture a house with the upstairs windows open. Warm air in the house will exit through the open windows. The entire house then becomes like a big chimney. As air flows out through the windows upstairs, air is drawn from downstairs to replace it. This is called the stack effect, since the house acts like a stack, or chimney. Open windows upstairs are just one cause. A poorly-insulated roof, a drafty attic, a tall stairwell, or anything else that allows a considerable amount of heated air to exit the house upstairs could create a stack effect problem. If the stack effect is powerful enough, it will overcome the chimney’s upward draft and pull replacement air (and smoke) into the house through the chimney.
  3. Competition for available air. Third, there must not be too much competition from other devices in the house, such as exhaust fans or air-exchange systems. If something else is sucking the air out of the house, the chimney might not be powerful enough to overcome it, and exhaust might be drawn into the house from the chimney.
  4. Proper chimney design. And finally, a chimney must be designed to accommodate the volume and type of exhaust being emitted by the appliances it serves. This involves correct sizing, adequate height, proper construction, and the use of appropriate building materials.

Since the chimney draft is affected by so many factors, draft problems can be complicated. We will cover diagnosis and correction of draft problems in the sections on fireplaces and stoves.

Checking a Chimney

Chimney safety should be a concern for every homeowner. Each year, lives and property are lost due to improper care and maintenance of chimneys. You can check some parts of the chimney yourself. We will review those below. But other parts need to be checked by a professional.

This is why you should have your chimney checked at least once each year by a chimney professional, and cleaned if necessary. In some cases, your chimney professional will advise more frequent visits.

In checking your chimney, a chimney professional can check all of the visible components of the chimney for damage, needed maintenance, and fire safety. A chimney professional is trained to look for dangerous or questionable conditions that a homeowner could easily miss. The experience he/she brings to the process of checking the chimney is well worth the modest cost.

Things you should know about your chimney:

  • Is the chimney structurally sound?
  • Was it constructed properly?
  • Is it lined?
  • Is the lining in satisfactory condition?
  • Are the appliances properly installed?
  • Does it require cleaning?
  • What other maintenance is required?
  • Is there a chimney cap on the chimney?

Things Homeowners Can Check:
Here are some things you can check. (But this doesn’t take the place of having the chimney checked by a professional.)

  • Condition of exterior chimney
  • Chimney Cap: is there one?
  • Leaks/Stains
  • Cleanout doors/base of flue
  • Visual check of flues
  • Condition of appliances & pipes

First, take a look at the chimney. Is there anything visibly wrong with it? For masonry chimneys, look for loose or missing bricks, chipped bricks or masonry joints, cracks, holes, a leaning chimney, or anything else that doesn’t look right. Use binoculars to check the chimney top. And if the chimney is exposed in the attic, don’t forget to check it there, also.

For metal factory-built chimneys, look for corrosion, loose sections, bending, any movement in windy conditions, and stains.

Any visible damage to the outside of a chimney is cause to have the chimney checked by a professional. If the outside is damaged, the inside could be in even worse shape.

Chimney Cap:
Is there a cap on the chimney? Water from rain and snow entering chimneys gradually damages the inside of a chimney. Joints between liner tiles gradually dissolve, and corrosive elements in exhaust from furnaces mix with water and slowly weaken the lining. Water pooling at the base damages the chimney structure. Freezing and thawing of water causes expansion damage. A good chimney cap reduces this damage by keeping most of the water out.

Caps with a screen mesh also keep animals out. Raccoons, squirrels, and birds often nest in chimneys. These animals can bring fleas and ticks into your home, as well as rabies, worms, and other diseases ­ and, of course, animals and their nests can clog the chimney.

And finally, a cap with a screen mesh helps keep sparks off the roof. So if you don’t have one, it is a good investment. Look for a cap that carries a lifetime warranty, and ask your chimney professional for a copy of the warranty card for your files.

Types of chimney caps. Some masonry chimneys have brick, stone, or concrete caps, raised above the top of the flues on brick or stone legs. Metal caps are also available. Stainless steel and copper caps offers superior durability, and often incorporate a screen mesh to keep animals out and keep sparks off the roof. Most factory-built chimneys incorporate a cap specifically designed to fit that brand of chimney.

Next, look for leaks or stains inside the house near the chimney. Peeling wallpaper, stains on the walls, and dampness near the chimney are sure signs of chimney problems. Sometimes these problems are caused by faulty roof flashing around the chimney. But sometimes the source is the inside of the chimney, and this can mean trouble. Missing or damaged flue liners, interior decay, or excessive condensation in the flue could be the culprit. Consult a chimney professional.

A note about condensation in flues: Today’s gas-fired appliances emit a considerable amount of water vapor. If not vented into a properly-sized flue, condensation in the chimney can become a serious hazard. If you have a gas-fired appliance connected to your chimney it is critical to have the chimney checked periodically by a chimney professional. Don’t make the assumption that just because there is no smoke, there is no problem with the chimney. Odorless, colorless carbon monoxide fumes from improperly-vented gas appliances can be fatal.

Safety Alert: Don’t check a flue that’s currently in use, such as a flue serving a wood stove that is lit or a furnace that is turned on. First, make sure the appliance is off. And remember wear gloves for protection. Open cleanout doors slowly! There may be a considerable buildup of soot at the base of the flue.

Base of the Flue:
Take a look at the base of the chimney (look in the cellar ­ or for chimneys built up the outside of the house, check the base outside, too). Look for one or more cleanout doors. Take a look inside the door. Using a small mirror and a flashlight, you can look up the flue from the bottom.

Some flues have bends in them, so you might not see all the way to the top. But take note of any buildup of soot or debris at the base of the flue, and on the flue walls as far up as you can see. But be aware that even if the base looks pretty clean, the rest of the flue isn’t necessarily clean. Most of the action takes place from the appliance up. So the chimney might still need cleaning.

While you are looking up the flue, try to spot any holes, cracks, or separations. But don’t panic if you see something that doesn’t look right. It takes a trained eye to determine just what’s going on in a chimney flue.

And lastly, you can check the condition of the appliances and connector pipes. Again, this doesn’t take the place of a professional check, but it will give you some ideas, and questions to ask.

Safety Alert: Wear protective clothing including eye and ear protection when looking up into chimneys.

Fireplaces. Check the brickwork for wear and breakage. Check the damper. It should open and close easily, without binding on anything. Look up into the smoke chamber, above the damper.

Does the smoke chamber look clean, or sooty? If there is any amount of soot up there, or if you haven’t had your chimney cleaned recently, have it checked and cleaned if necessary.

Wood Stoves. Check the condition of the stovepipe leading to the chimney. If it is rusty, soft, or has holes in it, replace it. Do you see any soot, creosote, or signs of leakage on the outside of the stove or stovepipe anywhere? This could signal an improper installation, and problems with the operation of the stove.

Check both the inside and the outside of the stove for cracks, bulges, warping, rust, or other signs of damage or wear. Most stove doors have a rope-style gasket around the edge for a good seal. Is the gasket in good shape?

Safety Alert: Pipes may be hot! Be careful!

Furnaces. Checking the internal components of a furnace is a job for a furnace technician. But you can check the connector pipe for signs of damage.

Look for rust, soft spots, or leaks. Be careful not to touch any electrical components, or anything attached to the connector pipe.

If you see anything amiss with the appliances or connector pipes, give your chimney professional a call and find out if immediate attention is warranted.

Here’s a trick for checking flues: Hold a small mirror in the base of the flue, and hold the flashlight so it is pointing at the mirror, from the same angle as your eyes. Then you’ll be looking (in the mirror) at the spot that the flashlight is illuminating. You can move the mirror around to see different parts of the flue. It is the same principle as the coal miner’s hat with a light on it. The light shines where you are looking. It takes some getting used to, but it works.

Chimney Fires

Chimney fires are serious! Temperatures in the chimney during a chimney fire can reach over 2000 degrees Fahrenheit – hot enough to destroy the chimney liner and possibly set the house on fire.

Some chimney fires go unnoticed by the homeowner. Others sound like a freight train running through the house, and display thirty- foot flames shooting from the chimney top. Either way, they are bad news.

Things to do if you have a chimney fire:

  • Call the fire department.
  • Get everybody out of the house.
  • If you have a chimney fire extinguisher, use it.
  • Close stove air inlets on stoves and glass doors (if you have them) on fireplaces.
  • Have the chimney cleaned and checked by a chimney professional before you use it again.

Some people think a chimney fire is a good way to clean the flue. They are wrong! Starting a chimney fire deliberately is foolish and dangerous. You could burn your house down.

And even if the house survives, you could cause thousands of dollars of damage to the chimney lining, or create hidden fire damage. Most chimneys have combustible materials in direct contact with the exterior surface of the chimney. If the chimney fire doesn’t catch them on fire, it might still scorch or bake these combustible materials, making them more likely to ignite next time. …Or the time after that. Play it safe, and leave cleaning the chimney to a chimney professional.

How can you avoid chimney fires? Learn to operate your fireplace or stove correctly, and follow a regular routine of chimney cleaning. Especially for wood stove users, proper operation and the use of correct fuel are essential. Long, slow burns or the use of green or wet wood can create dangerous creosote deposits very quickly, especially in older, less efficient stoves.

  • Creosote: A product of incomplete combustion: deposits of unburned, flammable tar vapors from wood smoke. Sometimes it’s 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.

Proper operation will not only reduce the risk of chimney fires, it will also increase the efficiency of the appliance, reduce pollution, and save wood.

Chimney Maintenance

At least once each year you should have your chimney checked and cleaned if necessary, by a chimney professional. If you heat with wood, or if special circumstances of your chimney system warrant it, it may be wise to have the chimney checked more frequently.

When’s the best time to have the chimney checked? If you haven’t had it done this year, then now! But for routine maintenance, early spring, after the heating season is over, is the best time. Chimney cleaning in the spring leaves the chimney free of corrosive and foul- smelling soot deposits during the hot, humid summer months. And in the fall, you will be ready for the cold weather.

Successful Fire Building

Tips for one-start fire building, and some basic information for homeowners, including:

The purpose of a stove or fireplace is to provide warmth, comfort, and atmosphere. The trick is to get those desired effect without the “undesirables,” those being lots of smoke, foul odors, house fires, and so on.

First we will talk about fire safety, the obvious first consideration. Then we will discuss building a fire. Firebuilding is something that most people seem to think they know how to do. Those who claim that they can’t build a fire are usually either unfamiliar with fireplaces and stoves, or just figure that someone else will do it if they plead ignorance.

In any case, lighting a fire in a stove or fireplace is not the same as lighting a campfire or firing up the barbecue. Even the most skilled pyrotechnic wizard runs the risk of a major flop by trying to light a fire in a stove or fireplace without knowing a little bit about the appliances and the right way to use them. Let’s launch right in.

Fire Safety

First thing’s first:
Checklist: Things to do before you light a fire.

  • Have the chimney checked by a chimney professional.
  • Know how to operate the fireplace or stove.
  • Have the right hearth tools and equipment.
  • Check your home’s fire safety equipment.

For the sake of fire safety, have your chimney checked at least once each year by a chimney professional. Your chimney professional will check to see if the chimney requires cleaning, and will also check for unsafe conditions in the chimney.

For details on having the chimney checked by a chimney professional, see “Checking a Chimney”.

And while you are thinking about fire safety, check your smoke alarms and fire extinguishers. Replace the batteries in smoke alarms regularly.

Many businesses are required to have their fire extinguishers inspected yearly. It is a good habit for homeowners, too. Local fire departments usually will inspect them for you, free of charge, or for a nominal fee. Make sure you have the right kind of extinguisher. It should be labeled with the types of fires it is designed for, but if you are not sure, ask your local fire department for more information. They also can generally provide you with information about establishing fire drill routines and exit routes for the safety of your family.

A little bit of preparation can prevent a lot more than a bad experience, and will put your mind at ease.

How to Build a Fire

Here we will discuss building a fire in a fireplace. For wood stoves, the procedure is pretty much the same, except you need to know how to operate the stove once the fire is lit.

After a quick tour of the things you need, I will describe the most common firebuilding technique (which is not to say it’s the only way to do it.)

Things you need to build a fire…

  • Seasoned firewood
  • Small splits of firewood
  • Kindling or fire starters
  • Crumpled newspaper
  • Matches

Seasoned Firewood:
A good fire requires not only a functional appliance, but good fuel. For best results, use seasoned firewood – wood that has been stored covered for the better part of a year. Season your wood under cover, but with good air flow.

Unseasoned, or green wood has too high a moisture content, and doesn’t burn well. Hard woods, like oak and maple, tend to be better than soft woods, like pine, since hardwoods have a higher BTU content, and will give a longer burn time and better performance.

A BTU is a “British Thermal Unit,” the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

While lower-quality wood will often burn acceptably in an open fireplace, most wood stoves call for more care in fuel selection.

Believe it or not, super-dry wood – like that pile that’s been out in the shed since you bought the place in 1972 – isn’t very good fire wood, either. It might work okay in an open fireplace (assuming it isn’t rotten), but it will burn fast and furious, and might throw a lot of sparks.

And all three – green wood, soft woods, and super-dry wood – create bigger problems when burned in wood stoves.

For the Facts & Figures Buffs:
The optimal moisture content for firewood is about 20% to 25%, while fresh-cut wood usually has a moisture content of 35% to 70%. The reason wet/green wood doesn’t burn well is that water has a high specific heat. (“Specific heat” is the amount of heat required to raise the temperature of one gram of a substance one degree Celsius.) It takes a lot of heat to boil the water away, so there is less heat to keep the combustion process going.

Lumber, Trash, & Other Things:
You probably already know that you are not supposed to burn anything other than seasoned firewood. Burning treated lumber, painted wood, trash, and such, releases toxic chemicals into the atmosphere (including your home!), and could cause other damage, as well. For example, a catalytic combustor in a wood stove can be destroyed by certain chemical agents found in these items.

Fireplaces and stoves aren’t incinerators, and it is neither safe nor environmentally sound to use them as incinerators. So recycle your pizza boxes and plastic wrap. Stick with seasoned firewood for your hearth, and do yourself, your home, and our environment a favor.

Artificial Logs. If you don’t want to deal with lugging and stacking firewood, or if you are out of wood and want to have a fire in your fireplace, you might try an artificial log. But be aware of the limitations. They are intended for use in open fireplaces, not in wood stoves; and they are designed to be used one at a time. If you have a factory- built fireplace, check the manufacturer’s instructions and see if they recommend the use of artificial logs.

There are many types of firestarters firestarters you can buy for use in open fireplaces, including impregnated chunks of composition material, wax-and-wood- shavings blocks, and oil-soaked ceramic starters. These usually take the place of the newspaper and small kindling, but you will probably still need some small splits of wood.

Read the instructions on the package, and be especially careful if you use an oil- type starter. Never use charcoal lighter fluid, gasoline, or anything else that’s not specifically designed as a firestarter for fireplaces. For wood stove users: check your owner’s manual before you burn anything with chemicals in or on it.

Newspapers are great for starting fires, but they aren’t a replacement for fire wood. Use enough to start the fire, and recycle the rest of the stack. And don’t use the sections with color print, especially the color glossy sections, which contain chemicals that are unsafe to burn. Use the plain, black-and-white parts.

Setting the Fire:
Put down a layer of crumpled newspapers, snug, but not crammed tightly together. You want space for air to get in, or you’ll have a smoldering pile of papers and an unimpressive result. In a fireplace, put the paper under the grate.

Next, put down a couple of handfuls of small, dry kindling: twigs and very small branches are fine, or very small splits of wood. Criss-cross them in a few layers, to allow air circulation. Don’t be stingy with the kindling. It is the key to a one-start fire.

Note: You can use fire starters in place of the paper and small kindling, but read about it first.

Then add a few larger splits, and top it off with a couple of small logs. That’s it. Your fire is set and ready.

Wait! Don’t strike that match yet!

Don’t Forget…

  • Is the damper open?
  • Do you need to prime the flue?

If you’re not sure, skip to “Smoky Startups”.

Once you are sure you are ready, light ‘er up. Wait a few minutes, until the larger splits and the small logs are well lit, and add another log on top.

Then sit back and enjoy.

Tools and Equipment


Hearth Tools…

  • Spark screen.
  • Poker/tongs.
  • Hearth broom.
  • Ash bucket and shovel.
  • Woodburner’s gloves.
  • Wood carrier and rack
  • Fire extinguisher
  • Chimney fire extinguisher

Go to your hearth products retailer and pick out a good set of tools. You’ll be happy later on if you spend a little extra for a good set. Flimsy tools, and tools with handles that unscrew easily or fall off, will drive you crazy and take away from the relaxation and enjoyment of the fire.

If you are using a fireplace, a spark screen is a must. If you have young children, you need a safety screen around a wood stove, as well.

Woodburner’s gloves will help you feed the fire, and avoid burning your hands. With good quality gloves, you can literally reach into the fire and move a log in emergencies.

To help in the task of lugging the wood from the wood pile to the living room, you will want a wood carrier. It is a wide fabric or leather sling with handles, that allows you to carry an armload without dropping logs or scattering wood chips everywhere. Some are designed like wide tote bags, for extra cleanliness. A sturdy wood rack by the hearth will keep your indoor wood supply safe and neat.

Don’t forget to have a fire extinguisher nearby, just in case. Another type of safety device is a chimney fire extinguisher. This looks like a large road flare. If you have a chimney fire, you strike it and place it in the firebox, and it emits a huge quantity of smoke, which stifles the chimney fire. Ask for details at your local stove shop, or ask your chimney professional.

Cleaning Up

For fireplaces:
Some fireplaces have a small, cast iron door called an ash dump door inside the fireplace in the center of the fireplace floor, or inner hearth. This door leads to the ash pit, an open cavity below the fireplace. If you have an ash dump door, you probably also have a cleanout door in the cellar or outside, at the base of the chimney.

Once the ashes are completely cold – which can take well over 24 hours – you can push them down into the ash pit, saving you the hassle of carting them over the white Persian rug. Later, if you feel so inclined, you can open the cleanout door and shovel out the ash pit.

Note: This is a very dusty job. Wear a respirator. Or better yet, hire your chimney professional to do the job, using a high- powered vacuum designed to filter out very small particles. And since the average ash pit is big enough that you can dump ashes down there for decades without filling it, don’t feel that you have to rush to clean it out.

Don’t shovel live coals into the ash pit, as combustible materials like plywood and 2×4’s are often left in the ash pit during construction of the house.

For Fireplaces with no ash pit, and For Wood Stoves:
Carry the ashes outside in a metal container, and store them in a metal can with a tight lid, on a non-combustible surface (like dirt or concrete). Many home fires are caused each year by hot ashes left on the back porch or in the garage – even if they are in a metal can! Ashes stay hot for an incredibly long time. So store them outside, away from anything combustible


A basic understanding of how fireplaces work will maximize your enjoyment and help prevent problems. In this section we will cover:

All fireplaces are not created equal. In fact, other than factory-built fireplaces, no two fireplaces are the same. Even if your fireplace seems identical to your neighbor’s (suppose, for instance, that you both bought the same model of factory built fireplace) they can behave very differently depending on how you use them.

Armed with some basic knowledge about the “hardware,” you will have better success in making your fireplace behave itself.

Types of Fireplaces

Traditional masonry fireplaces fall into two general categories:

Standard Fireplaces:
A normal brick fireplace, most of which have an opening about 36″ wide, about 28″ high, and are 16″ to 20″ deep. The inner walls of the fireplace angle inward, and the back sometimes slopes forward a bit, but is sometimes nearly vertical.

Rumford Fireplaces:
Count Rumford (Sir Benjamin Thompson), an 18th century philosopher and scientist, wrote a book on fireplace design that stands in stark contrast to the “standard” design. Designed to increase heat transfer to the room (and thus reduce heat loss up the flue), Rumford fireplaces incorporate a shallower firebox and a higher opening, with the sides and back quite slanted. These fireplaces often look as if they would certainly spill smoke into the room. But a properly constructed Rumford fireplace does, in fact, deliver what Count Rumford promises. If you are designing a new home, talk to an experienced mason about it.

The art of building Rumford fireplaces was almost lost; but modern masons are starting to look once more at his design, and Rumford fireplaces are finding their way more frequently into new homes.

Some newer types of fireplaces include:

Factory-built Fireplaces:
Fireplaces built in a factory, of steel, cast iron, firebrick, and other manufactured materials, and installed on site, generally with factory-built chimneys.

Masonry fireplaces with metal liners:
Standard brick or stone fireplaces incorporating a cast-iron or steel lining inside the fireplace.

Sometimes the metal liner incorporates an air space between two layers of metal. Ducts connected to this air space (usually you will see a grate on either side of the fireplace opening near the floor) draw cool air in at the base and vent warm air out higher (usually through another pair of grates above the mantel).

Modular/Masonry fireplaces:
A relatively new addition to the lineup, modular masonry fireplaces are built of pre- fabricated masonry sections, which are assembled on-site. Some systems are designed for retro-fitting to existing chimneys, as a replacement system for a damaged or non-functional fireplace.

Anatomy of a Fireplace

While there are differences among the various types of fireplaces, you will find several common parts. An understanding of the basic terminology is helpful.

Outer Hearth:
This is the technical term for what we usually call the hearth. It is the part of the hearth that extends out into the room, beyond the fireplace opening.

Inner Hearth:
The floor of the fireplace, inside the opening.

This is where you build the fire.

The rear wall of the firebox.

A plate or valve that closes the fireplace flue when the fireplace is not in use. You must fully open it before lighting the fire.

Throat damper:
A damper located in the throat of the fireplace, just above the firebox. This is the kind found in most fireplaces, and is operated by means of either (a) a handle inside the firebox or (b) a knob above the fireplace opening connected to a rotating metal shaft attached to the damper.

Top-sealing damper:
A damper located at the top of the chimney, operated by means of a cable extending down the flue to a handle in the firebox.

Smoke Chamber:
The roughly-triangular space above the throat of the fireplace leading up to the flue.

The vertical passageway up the inside of the chimney.

Ash dump door:
A metal door located in the inner hearth of some fireplaces, which leads to an ash pit.

Ash Pit:
A cavity underneath a fireplace firebox, used as a receptacle for ashes, and accessible for cleanout by means of a cleanout door.

Ash pit cleanout door:
A metal door located at the base of the chimney which leads to the ash pit, facilitating cleanout of the ash pit.

How to Use the Fireplace

If you have never used the fireplace before, or if it has been over a year since you have had it checked by a professional, have your chimney professional check the fireplace and chimney before you use it.

Ask him/her about how the damper works, and for any observations that might point to potential problems with the fireplace. Chimney professionals are trained to check the venting system and spot possible hazards that a layman would miss.

Essentially, using the fireplace is a matter of opening the damper, setting the fire, and lighting it – there’s not much to it! A day or so later, when the fire is completely out, including the coal bed, you should close the damper again, to prevent heat loss up the flue.

But before you start your first fire, read about Fire Safety and How to Build a Fire.

Fireplace Accessories

A good set of fireplace tools is a necessity, of course. At minimum, you will want a poker, a hearth broom, and a shovel for ash cleanup. Other useful tools include a set of tongs for moving logs, and a hoe for moving ashes around (especially useful in pushing ashes into the ash pit).

Some people also like a bellows, for blowing air into the coal bed to start a faltering fire (and for decoration).

Building fires directly on the inner hearth isn’t a good idea, unless you have a factory-built fireplace that’s specifically designed without a grate. Fires built right on the floor of the firebox don’t usually burn as well, since it is harder for air to get in. Also premature wear to the inner hearth might occur.

If you don’t have a grate, take measurements of the inner hearth’s depth, width in front, and width in back. Go to your local stove shop and pick one out. A heavy cast-iron grate will last much longer than a grate made of welded steel bars. If you plan to use the fireplace often, spend a little extra for a good cast-iron grate.

Some people use andirons in place of a grate. But as logs burn down, andirons will no longer hold the logs up. They will collapse to the floor of the firebox. So even if you have andirons, a grate is still a good idea. You can keep the andirons for decoration and ambiance. Just slide the rear legs under the grate, or put one on each side if they are too tall to fit under. You can also buy special short shanks for andirons at a stove shop. These are replacement rear assemblies for andirons (equivalent to the part you set the logs on) but they are very short front to back, so you can place the andirons fully in front of the grate. You just unbolt the old assembly and bolt these on instead. Bring one of your andirons to the stove shop so you can check to see if they will work before you buy them. Short shanks for andirons are also useful for people who have a shallow firebox and glass doors covering the fireplace opening. You can place the andirons with short shanks outside the doors on the hearth (just for decoration, of course).

Spark Screen:
A must. You can choose from hanging mesh screens that slide open, rigid or folding screens that stand in front of the opening, or attached “gate” style screens. If you don’t have a screen, or if yours is worn out, measure the height and width of the fireplace opening and the amount of clear space around the opening (the clearance to a mantel, or exterior damper handles, etc). Take your measurements to your local stove shop and pick one out.

Fireplace Doors:
Highly recommended. These are tempered glass doors in a metal framework, sized to fit your fireplace opening. Most incorporate a hanging mesh or gate-style screen, and some sort of louvers to adjust air flow to the firebox when the doors are closed.

The main advantage of a set of fireplace doors is that you can close them before you go to bed, minimizing heat loss up the flue – because you can’t close the damper until the fire is completely out, usually a day or more later.

Also, if the fireplace should start to smoke due to wind conditions or other problems, closing the doors will often prevent smoke from continuing to enter your home.

Some common types of fireplace problems can be solved with doors, as well. We will discuss these in the problem- solving section.

A word of advice: Don’t let sticker shock scare you away from purchasing a good set of doors. The quality difference between a $100 set and a $600 set is immense. The fireplace is the focus of your living room, and a valuable asset. Choose a set of doors that offers durability and beauty, and each time you use the fireplace, you will be glad you spent the extra money. A cheap set of doors will look good for a year or so, then drive you crazy as the doors buckle and bind, the finish wears off, and the focus of your living room turns into an eyesore.

Fireplace Inserts:
Fireplaces are not designed to be efficient heaters. And in an effort to get more heat from a fireplace, some homeowners install a fireplace insert. There are several types of inserts available, from high-efficiency wood stoves designed to be installed in a fireplace, to hollow grates with a fan to circulate heat into the room.

If you are considering the installation of an insert, do some homework first, or you may be sorely disappointed.

First, decide what your expectations are. If you want this fireplace to heat your home, you will need a high-efficiency modern woodstove with enough power to heat the house.

In the 1970’s we used to just slide a stove into the fireplace and light ‘er up. But we found (often the hard way, through chimney fires and tragic losses) that this isn’t a safe installation.

To install a woodstove properly and safely insert requires, at minimum, connecting the stove up through the smoke chamber and into the chimney liner, which usually starts five feet or more from the fireplace floor. This involves the use of listed chimney liner parts specifically designed for this purpose. Sometimes an entirely new liner is needed, to size the flue for the stove properly. In any case, this is a job for an expert. Go to your local stove shop and ask about an insert.

Bringing some basic measurements with you will help.

Note: Don’t be discouraged if you can’t get all these measurements. Your stove installer will probably want to visit and take exact measurements, anyway. This will simply help you get an idea of what will fit, and the cost.

Measurements needed for a fireplace insert installation…

  • Height and width of the fireplace opening.
  • Width of the firebox in the back
  • Width of the throat or damper opening (usually 6″ or less).
  • Height of the flue liner above the floor of the firebox (Try extending a tape measure from the damper, up through the smoke chamber to the liner, then measure from the damper to the floor of the firebox, and add them.).
  • Size of the flue liner (best estimate).
  • Overall height of the chimney (from the floor of the fireplace to the top).
  • Width and depth of the outer hearth (that’s the hearth extension into the room).
  • Height of a wood mantel above the fireplace opening.
  • Distance from the opening to wood trim or mantel legs (needed to figure adequate clearances to combustible materials around the fireplace).
  • Rough idea of how big an area you want this stove to heat.

Solving Fireplace Problems

Using your fireplace should be a relaxing, enjoyable experience. But if it isn’t, due to some annoying problem, don’t give up on it! Chances are the problem can be corrected without major surgery. Let’s take a detailed look at common fireplace problems and how to solve them. We will look at:

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

The Troubleshooting Guide section on fireplaces, 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.

Smoking Fireplaces

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:

  • Smoking 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.

Smoky Startups

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…

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.