Fireplace & chimney FAQ

Why you need a knowledgeable hearth professional

You’re choosing an appliance that can bring years of warmth and comfort to your home — if it’s installed properly.

Harnessing the beauty and warmth of fire for the home is not a do-it-yourself project or something you should necessarily trust to the lowest bidder. The hearth in any home is a focal point and a center for family enjoyment. As such, it calls for important decisions about the appropriate appliance or products for your goals. Proper placement, venting and protection from combustibles are very important considerations. Both for safety and for performance, hearth products require considerable technical knowledge and skill in designing and installing them.

How to choose a chimney sweep

The chimney service trade is not regulated, nor are chimney sweeps licensed in most states. Opening a chimney service business requires a relatively small capital investment. Virtually anyone — without education, training, experience or even a working knowledge of proper tools or equipment — can become a chimney sweep. As a result, many ill-equipped and ill-prepared individuals are free to offer their “services” to homeowners.

Many of those individuals take advantage of learning opportunities and become competent, qualified chimney sweeps. Others continue along the same path they started on, offering incompetent service and in some cases providing trusting homeowners with a false sense of well-being. For this reason a number of states are considering license requirements for chimney sweeps, and some municipalities already license them — in most of those, the criterion for licensing is the CSIA Certified Chimney Sweep credential.

That credential is the hallmark of excellence among chimney service professionals. There is only one legitimate national certification program for the chimney service industry, and that is the CSIA program. Those who have earned the credential have passed an extensive examination on national codes and standards and have agreed to the CSIA Code of Ethics.

How often your chimney should be cleaned and inspected

This is a tougher question than it sounds. The quick answer is the national safety standard: NFPA 211 says “Chimneys, fireplaces, and vents shall be inspected at least once a year for soundness, freedom from deposits, and correct clearances. Cleaning, maintenance, and repairs shall be done if necessary.” That standard takes into account the fact that even if you don’t use your chimney much, animals may build nests in the flue, or other deterioration may have made the chimney unsafe to use.

The Chimney Safety Institute of America recommends that open masonry fireplaces are cleaned at a quarter inch of sooty buildup, and sooner if there is any glaze present in the system. Factory-built fireplaces should be cleaned when any appreciable buildup occurs. That is considered to be enough fuel to cause a chimney fire capable of damaging the chimney or spreading to the home.

Blockages are not folklore

Storks nesting in chimneys were once believed to bring good luck, according to European folklore. In fact, nests in chimneys — or blockages of any kind — are nothing short of bad news. They cause smoking problems, chimney fires and carbon monoxide poisoning.

Residential chimney fires remain a significant, and largely preventable, cause of injury, death and property damage. In a widely cited United States Consumer Product Safety Commission study of 1998 — the figure this page has quoted for many years — 18,300 residential fires originated in chimneys, fireplaces and solid fuel appliances, resulting in 160 injuries, 40 deaths and $158.2 million in property damage. Both the CSIA and the National Fire Protection Association recommend yearly chimney inspections to help prevent these hazards, and virtually all such fires are preventable.

Many American homeowners think their chimneys only need to be cleaned and inspected if they burn wood. But almost all heating appliances — gas, oil, wood or coal — rely on the chimney to safely carry toxic gases produced by the heating system out of the house. A carbon monoxide detector can warn you of potential poisoning after the gas has already entered the living area; an annual chimney check helps prevent it entering in the first place.

Each fall homeowners shift into home-improvement mode. They clean gutters, garages and basements, preparing homes for winter. But they usually don’t inspect, repair or clean their chimneys, despite the potential damage to their property or even their lives. An annual inspection by a CSIA Certified Chimney Sweep® is a modest investment that reduces the danger of chimney fires and carbon monoxide poisoning. When chimney fires do occur, many insurance investigators rely on CSIA Certified Chimney Sweeps to determine whether a fire originated in — or damaged — the chimney system.

Why your chimney needs a liner

A flue lining in a masonry chimney is defined as “a clay, ceramic, or metal conduit installed inside of a chimney, intended to contain the combustion products, direct them to the outside atmosphere, and protect the chimney walls from heat and corrosion.” Building codes vary from one state or locality to another, but flue lining has been recommended since the early part of the last century, and most fire codes now mandate liners.

In the 1940s and again in the 1980s, masonry chimneys were tested by the National Bureau of Standards for durability, because of rising concerns about their performance and safety. The tests revealed that unlined chimneys were so unsafe that researchers characterized building a chimney without a liner as “little less than criminal”.

Liners serve three main functions

1. The liner protects the house from heat transfer to combustibles. In the NBS tests, unlined chimneys allowed heat to move through the chimney so rapidly that adjacent woodwork caught fire in only three and a half hours.
2. Liners protect the masonry from the corrosive byproducts of combustion. If flue gases reach the brick and mortar, the usable life of the chimney is reduced. The gases are acidic and literally eat away at the mortar joints from inside. As the joints erode, heat transfers more rapidly to nearby combustibles, and dangerous gases such as carbon monoxide can leak into the living areas of the home.
3. Liners provide a correctly sized flue for optimum appliance efficiency. Modern wood stoves and gas or oil furnaces require a correctly sized flue to perform properly. The chimney not only allows the products of combustion out of the house — the draft it generates also supplies combustion air to the appliance. An incorrectly sized liner leads to excessive creosote buildup in wood burning stoves, and to the production of carbon monoxide with conventional fuels.

The three types of chimney liner

Clay tiles are the most common type of masonry chimney liner. They are inexpensive, readily available, and perform quite well for open fireplace chimneys that are properly maintained. There are two disadvantages. Being a ceramic product, they cannot rapidly absorb and evenly distribute heat during the rapid temperature rise of a chimney fire; the uneven heating produces unequal expansion, which cracks and splits the tiles apart — much like immersing a cold drinking glass in very hot water. A chimney with cracked liners must be repaired before use. Second, tiles cannot adequately contain the liquid combustion byproducts produced by modern gas appliances.

Metal liners, usually stainless steel or aluminum, are primarily used to upgrade and repair existing chimneys. These systems are UL tested and listed, and if properly installed and maintained they are extremely safe and durable. Stainless steel is suitable for wood burning, gas or oil applications; aluminum is an inexpensive alternative for certain medium efficiency gas applications only. High temperature insulation is usually required with the liner for safety and performance.

Cast-in-place liners are lightweight, castable, cement-like products installed inside the chimney, forming a smooth, seamless, insulated passageway for the flue gases. They can improve the structural integrity of aging chimneys, and they are permanent liners suitable for all fuels.

Considering the dangers of old unlined or damaged chimneys, and the many cost effective options now available to make them safe components of the home heating system, we suggest you have your chimney professionally inspected to be sure it meets modern safety standards.

Ten reasons a fireplace doesn’t work properly

Why fireplaces work, and how best to build them, has been a topic of hot debate for centuries. From the first stone rings stacked around the campfire to modern factory-built fireplaces with carefully engineered dimensions, there has been a steady evolution of design intended to make them draw well and cast as much heat as possible. Most of that evolution has been by trial and error, and some designs work much better than others.

Simply put, fireplaces work because hot air rises. When you start a fire the air inside the chimney becomes warmer and less dense than the air outside, so it starts to rise. As the warm air rises, cooler air from the room flows into the firebox, fanning the fire and creating more heat in an ongoing cycle. Pressure differentials as wind moves across the top of the chimney play a part too.

There must be at least a hundred reasons why a fireplace may not function properly. Below are the common ones, from the obvious to the more arcane. Bear in mind this is a simplified list — a true understanding of fireplaces requires extensive knowledge of air flow patterns, pressure differentials and construction technique. If none of this solves your problem, hire an experienced, certified chimney sweep. Often the problem is obvious to someone with enough experience, once they can actually look over the entire situation.

1. Is your damper fully open? Everybody eventually forgets to open the damper. Many dampers also stop opening fully because of water damage or soot buildup behind them on the smoke shelf. A good professional cleaning usually solves this.
2. Is your firewood green or wet? The main reason your fireplace works at all is the heat inside the chimney. If the wood is not dry and well seasoned it makes more smoke than heat, and there may simply not be enough heat for the chimney to work.
3. Is your chimney dirty? Thick layers of soot physically restrict the flue, but even a quarter to half inch of buildup makes more difference than you might think — a half inch restricts air flow by 17% in a typical masonry chimney and by a whopping 30% in the average prefab. Birds and small animals also think your chimney looks like a hollow tree; sweeps often find chimneys packed with leaves, twigs and baby animals. The solution is a good cleaning and a chimney cap.
4. Is your chimney tall enough? To function properly a chimney should be at least ten or twelve feet in overall height. Where it projects above the roof it should be at least three feet tall, and at least two feet higher than anything within ten feet of it — including other buildings and trees. If your fireplace smokes because the chimney is too short, the problem is usually worse when the wind blows.
5. Is your flue large enough for the fireplace opening? The rule of thumb is that the area of the fireplace opening can be no more than ten times the area of the flue (twelve times for round flues). An undersized flue can’t handle the volume of smoke, and some of it spills back into the room. Since there is no practical way to enlarge the flue, the fix is usually to make the room opening smaller with metal smoke guards or creative masonry. There are also prefabricated refractory firebox retrofits that work well at a 15:1 ratio and deliver twice the heat of a conventional firebox.
6. Is your chimney on the outside of the house? Warm rising air is the engine here. A large masonry chimney on an outside wall gets very cold, and the air inside it wants to fall down the chimney instead of rising — sometimes even a day or two after it has warmed up outside. These chimneys can be hard to start and may smoke as the fire burns low. Many people light some rolled-up newspaper and hold it near the damper to get that cold plug moving upwards; keeping a moderate but brightly flaming fire also helps.
7. Is your home too tight? Fireplaces need large volumes of air. Picture a 12″ × 12″ column of air rising up your chimney the entire time the fireplace is working. That air comes from inside the living area and has to be replaced. Modern insulation and weather-stripping often leave nowhere for it to get back in, so the fire burns sluggishly and smokes. Opening a window on the windward side is a temporary fix. It can also lead to very dangerous carbon monoxide buildup if the fireplace and furnace compete for combustion air — find a permanent solution at once.
8. Your house can also be too loose. A house that leaks a lot of air at the upper levels can set up its own chimney effect, strong enough to overpower your fireplace chimney — particularly if the fireplace is in the basement on a cold exterior wall. Make sure the attic access door is in place and all upstairs windows are tightly closed.
9. Is there a return air grille in the same room? As the fireplace consumes air and cold air moves in to replace it, the furnace is likely to come on. When it does, air is drawn into the return, competing directly with the needs of the fireplace.
10. The other ninety-one reasons mostly come down to design problems from when the fireplace was built. As well as being too short or too small, a chimney can be too large, too tall, too crooked and so on, ad infinitum. Most of these are fairly technical, and again a good sweep may be your best bet.