Frequently Asked Questions

Q. How often should I have my chimney cleaned?

This a tougher question than it sounds. The simple answer is: The National Fire Protection Association Standard 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.” This is the national safety standard and is the correct way to approach the problem. It takes into account the fact that even if you don’t use your chimney much, animals may build nests in the flue or there may be other types of deterioration that could make the chimney unsafe to use.

The Chimney Safety Institute of America recommends that open masonry fireplaces should be cleaned at 1/8″ 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. This is considered to be enough fuel buildup to cause a chimney fire capable of damaging the chimney or spreading to the home.

Q. My fireplace stinks, especially in the summer. What can I do?

The smell is due to creosote deposits in the chimney, a natural byproduct of woodburning. The odor is usually worse in the summer when the humidity is high and the air conditioner is turned on. A good cleaning will help but usually won’t solve the problem completely. There are commercial chimney deodorants that work pretty well, and many people have good results with baking soda or even kitty litter set in the fireplace. The real problem is the air being drawn down the chimney, a symptom of overall pressure problems in the house. Some make-up air should be introduced somewhere else in the house. A tight sealing, top mounted damper will also reduce this air flow coming down the chimney.

Q. When I build a fire in my upstairs fireplace, I get smoke from the basement fireplace.

This has become quite a common problem in modern air tight houses where weather-proofing has sealed up the usual air infiltration routes. The fireplace in use exhausts household air until a negative pressure situation exists. If the house is fairly tight, the simplest route for makeup air to enter the structure is often the unused fireplace chimney. As air is drawn down this unused flue, it picks up smoke that is exiting nearby from the fireplace in use and delivers the smoke to the living area. The best solution is to provide makeup air to the house so the negative pressure problem no longer exists, thus eliminating not only the smoke problem, but also the potential for carbon monoxide to be drawn back down the furnace chimney. A secondary solution is to install a top mount damper on the fireplace that is used the least.

Q. I heat with gas. Should this chimney be checked too?

Without a doubt! Although gas is generally a clean burning fuel, the chimney can become non-functional from bird nests or other debris blocking the flue. Modern furnaces can also cause many problems with the average flues intended to vent the older generation of furnaces. We suggest you check the areas on gas and carbon monoxide for more information.

Q: What is level 3 creosote?

I have an 80 year old home that was a longtime rental house. I have lived here five years and have been using the fireplace for four of those years. I do not know how long it has been since my chimney was swept (potentially decades, if ever). I just had a chimney sweep at my house and he informed me that the creosote in my chimney was quite thick (he used the term “level 3” creosote). He also said that in the smoke chamber, the brick is stepped (instead of smooth) and that there is a lot of dangerous buildup in there. He recommended two applications of an acid cleaning (which he said are not entirely foolproof, and work better above 45°F) and that we use a chemical when we burn our fire to help “chalkify” the creosote buildup. He showed me the buildup inside with a light and everything he said seemed to make sense. Does this sound like it’s on the up and up? I can’t find any info on this acid cleaning and I would like to know if this sounds like it is the proper course of action in a case like mine.

What you have described sounds pretty typical. In addition to the chemical treatment that you mentioned, professional-grade chemicals, usually in the form of a powder, can be applied by chimney sweeps to help change the nature of the glazed creosote to a form that can be removed by a professional with a brush Both forms of these products require some heat such as you would find in a small fire in the fireplace.

If the creosote is gummy, about the only way to deal with the creosote is with a chemical treatment or with an acid application. Acid applications are not as commonly used since they are harder to apply and have to be neutralized a few days after application. If the creosote is crusty or fractures when hit (as opposed to gummy) a rotary cleaning can be helpful. Read our position statement on chemical chimney cleaning products here.

Q: How do I know if he really cleaned my chimney?

In the past, sweeps we’ve hired have always gone on the roof, checked the flashing, the mortar and all the workings of the chimney and then cleaned the chimney from the top of the house. Today, this sweep came in, looked into my fireplace from the bottom and said we didn’t need it cleaned because he can still see the bricks. My spouse asked to have it cleaned anyway. He then grabbed a wire brush and simply rubbed away any build-up from the main opening to the fireplace without even going up into the chimney to clean anything. Am I way off base, or did the sweep charge me without cleaning my chimney?

Your past experiences with chimney sweeps sound as though the sweep did the job he was hired to do. However, your most recent experience sounds a bit odd. If the sweep agreed to do a complete sweeping and only cleaned the brick in the fireplace firebox, you did not get the service that you paid for. A complete chimney sweeping includes the chimney flue and smoke chamber.

In the future you could ask for a Level 1 chimney inspection and a chimney sweeping. If the sweep doesn’t know what a Level 1 inspection is, find one that does. A Level 1 inspection is detailed in the National Fire Protection Association 211: Standard on Chimneys, Fireplaces, Vents and Solid Fuel-Burning Appliances.

Q: How common is it that chimney liners cannot be seen from inside the fireplace using only a flashlight?

Is there some standard building requirement for the flue and the fireplace that you can’t just look up from the fireplace and see the sky or chimney cap at the top of the chimney?

Flues are allowed to have up to 30 degree offsets. In most cases this will make a direct visual observation of the flue impossible. A video scan would be required to evaluate the flue condition.

The height of the chimney flue is not a factor. There is a big difference in what is observed between a visual inspection and a video inspection, even in short flues.

A Question About Relining

“I am in the process of accepting bids from various companies to have my chimney relined. I need some education on proper fit of the area between my furnace and the flue.

My furnace has an 8″ exhaust. Most of the estimates I have received involve the technician fabricating some sheet metal that funnels down from the 8″ pipe to connect to a 6″ liner that then goes up the chimney. The furnace in question is an oil furnace boiler that does double duty as my water heater. Most of my estimates for liner replacement are predicated on use of 6″ stainless steel tubes to bypass the eroding masonry that now exists. They would then hook up directly to my furnace which currently uses an 8″ exhaust to connect to the chimney. I am not sure how this will be accomplished in all cases, but I have been advised of several different methods.

One company pointed out that the difference between the size of the existing exhaust pipe and the liner could negatively affect the draw of the chimney. They stated that the inside of the chimney needed to be gutted, after which it would be able to accommodate a 7″ liner. This would result in the difference between the exhaust pipe and the liner of only 1″ and that would be sufficient to ensure proper draw.

I have also been told that most modern furnaces use a 6″ exhaust port. This further complicates matters, since the furnace I now have is very old and the end of its service life is probably sooner than later.

A 6″ liner would fit easily inside the brick chimney, but accommodating a 7″ stainless liner would necessitate rebuilding the chimney. This would increase the cost by 100% over other estimates. My question is, can I use a 6″ liner with an 8″ exhaust pipe from the furnace and still safely operate my furnace?

This leads me to several different scenarios:

Do I pass down a liner through the chimney but not connect it directly to the exhaust port of the furnace?

Do I connect to existing machinery with a 6″ liner or a 7″ liner?

If I connect with a 7″ liner and later have to replace the furnace, am I faced with having to replace the 7″ liner with a 6″ liner so as to fit the new exhaust?

Do I preemptively replace the furnace and the liner at the same time? My furnace is approximately 15-20 years old, but has been well-maintained and currently has no real problems.

As a bit of history, I currently own my house outright and WILL be moving within five years to a different location entirely. I do not want to sink any money into this house that is not necessary. I absolutely want to ensure that my furnace operates safely so I don’t just camouflage problems so I can sell my problems to someone else. I also want an honest job done for a reasonable price. Could you offer me your opinion of which option to focus on?”


If you go with the 7″ liner, and the sizing charts allow it that would be a reduction of only one size. When you go to sell your home, this reduction of one size from the previous 8″ liner could be justified with sizing charts. The building inspectors will often allow for a reduction of one size if it is an engineered system.

If you have occasion to change out the furnace, the 7″ would be a step up of only one size and it should work just fine. You might consider having the flue insulated to reduce condensation inside the flue, especially with the future new appliance that would be a higher efficiency unit. Learn more about chimney liners here.


Your advice tells me that the cheap way (put in the least expensive 6″ liner and keep the furnace I have) is not a good idea from a safety perspective and it is not a long term fix of the overall problem. The 7″ liner would work, but it would set me up to select the most expensive solution, vis-a-vis the liner, and then I would spend more money later adapting a new furnace should the need arise.

The difference in cost between putting a 7″ liner in the existing chimney and a 6″ liner is $1,100. If I put in the 6″ liner, I can put the $1,100 into the purchase price of a new furnace that already requires a 6″ liner. Then, in five years when I go to sell the house, it will have a five year old, high-efficiency furnace instead of one on its last legs. A new more-efficient furnace will also allow me the added benefits of fuel cost savings over that five year period. A 6″ liner will allow me room to follow your suggestion to insulate the flue. And last, but certainly not least, for the next five years, every time I hear the furnace kick on I won’t have to worry if it is going to break down on me or fill my home with carbon monoxide.