Chimney Draft Problems

When a chimney is having drafting problems there are many issues that can arise. Similarly, there are many reasons that a drafting problem may occur. A chimney that is improperly sized can cause a drafting problem to occur. Also, a chimney that is too close to nearby trees or other tall buildings can also develop a drafting problem. When a chimney does not draft properly, you can have multiple problems including smoking issues, creosote build up, and a cold draft in the winter.

By altering the ratio between flue and firebox size draft problems can be eliminated.
Chimney draft problems can be a real pain but there are chimney draft stoppers available to solve such issues.

When a chimney flue is too small for a firebox, smoke cannot draft up through the chimney. Round flues should have a 12:1 ratio to the firebox. Chimney systems that do not comply with this ratio will, generally speaking, have draw problems. One chimney draft stopper in this situation is a Smoke Guard. A Smoke Guard will actually reduce the size of the firebox to help it draft better. A properly sized firebox will draft properly. A Smoke Guard will also prevent a cold draft from coming down the chimney in the winter.

Another chimney draft inducer is improper chimney height. The chimney needs to be the highest point for about ten feet around in order for it to draw properly. Poor draft is absolutely of an issue because, first and foremost, it decreases your fireplace’s efficiency. A fire burns the warmest when there is a steady flow of oxygen. When a chimney doesn’t have enough air inside the home to continually supply it, it has to start to draw air from the outside, that is, down through the chimney. This is known as negative pressure inside your home, and this is the reason that many people experience smoking problems when you burn a fire. This negative pressure issue plays into chimney height issues and surrounding trees. If the chimney is too short then it is less difficult for a fire to start drawing air from down the flue system, and nearby trees can actually help force air down the chimney. One of the best ways to help turn your negative pressure to positive pressure is to crack a window near the fire when you are burning one. This will give the fire a fresh air source to draw from correcting the downdraft.

Poor chimney draft is a real pain and it can actually contribute to creosote build up in your flue system. Creosote, before it turns into a sticky or even glazed substance in your flue system is a gas, a product of combustion from the fire burning. When the flue system stays warm the products of combustion can float safely out of your chimney, however, if there is cold air being sucked into the chimney due to a draft, more creosote will solidify and stick in the flue system than will float away.

All of these problems presented by a drafty chimney can generally be corrected. Installing a stainless steel liner will reduce the size of a flue system that is too large. This is a means of fixing an improperly sized flue system, opposite to using a Smoke Guard to reduce the size of a firebox that is too large. There are special, top sealing chimney caps that will

Seal of the top of the chimney and eliminate your poor chimney draft problem. By sealing the top of the flue system you prevent cold outside air from entering the home through the chimney.
Seal of the top of the chimney and eliminate your poor chimney draft problem. By sealing the top of the flue system you prevent cold outside air from entering the home through the chimney.

eliminate draft when the chimney is not in use. These chimney caps have a damper system that will completely seal off the top of the chimney when closed in order to prevent cold air from coming down the chimney and into the home. Finally, if your chimney height was not correct, say it was constructed too short, adding a few feet of height onto the chimney will help it to draw properly. This is one of the more extreme draft fixes, however.

All of these chimney draft stoppers combat chimney draft inducers in different ways. You may want to call a chimney professional to diagnose exactly why your chimney is experiencing a drafting problem or any of the problems that come with a drafting problem. After diagnosis, repair is usually straightforward.

Clay Lamb
Latest posts by Clay Lamb (see all)

9 thoughts on “Chimney Draft Problems

  1. my parents have a 3 flue masonary chimney. One for furnace and waterheater, 1 for first floor wood burning fireplace and 1 for the lowerlevel fireplace (never used).

    Late last fall they had the chimney inspected, cleaned and a new damper installed on the first floor fireplace. The contractor also put a cap on that outlet.
    Now they are having a smoke issue everytime they go to use the first floor fireplace. unless they open one or two windows they get smoke smell into the house, and really strong in lower level. The company has been back once and adjusted the new damper but still no difference. Now they are trying to get them to do more changes (extend or reline). I say just have the new cap removed. Help….

  2. For now I would agree with you on removing the chimney cap. But I say that I feel if a fireplace was constructed properly it should be able to draw, even if it has a chimney cap on it. I also believe all chimney flues need a cover. Essentially you have a hole in the top of your house that can let water in. Even though you may have never observed the water, but I can assure you it is coming down the chimney and going somewhere.

    One way or another it sounds to me that your parents are experiencing a negative pressure or thermosyphoning problem. The smoke is either being pulled down the chimney to the basement, or the smoke chamber in the basement is sucking smoke from the upstairs firebox.

    As you mentioned the fireplace on the lower floor was never used, and since the house was built, I will assume that new windows, insulated doors, and new insulation has been added to the attic. Bathroom and attic fans may have been added. All of these items will change the air balance in a home, and create negative pressure in the home that the fireplace(s) will now have to compete with to get their required make up air so they can to operate properly.

    Often in a situation as your describing, extending the chimney flue will help. As a service call, we often will provide a temporary flue extension until the customer is totally satisfied that the added height has resolved their smoking issue.

    The idea of relining is an expensive option and I would only consider it, if you are able confirm that their is a chimney flue smoke cross over problem. Sometime turning lights off and using a bright flash light will identify how the smoke is moving in the room or within the chimney. I actually had one customer where we pulled his dirty furnace filter out, the fireplace quite pulling the air off of the basement floor and could then actually pull the air from the upstairs rooms.

    Lastly, the outside air vent found in most fireplace is really insufficiently sized. You can continue playing around with opening the window to see if the air supply is the problem. Now days air balancing in our home can be very delicate.

    As always I say start with the least expensive option first, as it seems to always be a process of elimination.
    I hope this helps.
    Burn Safe and Warm

  3. My first floor fire place will not draft well enough to keep my house from filling with smoke when used. Let me backup and try to describe my fireplace layout. We have a 1560 sq ft ranch with a full basement. There is a fireplace in the basement and one above it on the main floor. These are both standard masonry fireplaces built around 1958. The basement fireplace has a single 8″ x 13″ flue and the main floor fire place has two 8″ x 13″ flues, there is also an additional 8″ x 8″ flue which I believe at one time was used for an oil furnace. The flues come up through some decorative stone work which is about 6′ x 2′. The length of the flue is approximately 10′ for the main floor and 18, for the basement fireplace. The basement fireplace has a 28″ x 20″ opening and the main floor fireplace is on and outside corner which allows intake from 2 sides has a opening of 44″ x 24″.
    When I have started fires in the main floor fireplace I have had the house fill with smoke, I did notice that during this time I was seeing residual smoke flowing back down through the basement flue. I went ahead and capped the basement fireplace but I still don’t seem to be drafting correctly because we still get smoke in the house. I also would like to at sometime use the basement fireplace. I did verify that there are no voids between the flues.
    Any thoughts on where to go from here


  4. Anytime there are smoking problems there are many different issues that could be playing a factor. Anything from the height of the chimney to negative air pressure in the house. I would have a Chimney Sweep come in and take a look. It is a process of elimination.

    Burn Safe and Warm

  5. Hello

    Because my existing brick chimney does not meet the zero-zero clearance insurance specs for Canada, and hasn’t been used for a decade, I am planning on placing an insulated chimney-pipe in for my new wood stove. Unfortunately, a 6″ insulated pipe may not fit the existing chimney, and I have been advised to go with a 5.5″ pipe. Might there be any worry of draft (draw) problems with a 5.5″ pipe if my new stove exhaust is 7″, and my chimney height is 25feet with good outside clearance?

    Grateful for advise,


  6. Not sure of Canadian installation codes. In the USA most local building code would not allow you to down size the chimney venting pipe. Also I would recommend checking with the stove manufacturer to see what their installation specifications are “in writing”. Always follow the manufacturer’s installation instructions. If “bad things” were to happen, there could possibly be insurance claim payment problems.
    Burn safe and warm.

  7. I’m converting my natural burning fireplace back to gas. We purchased this home recently, and from the looks of things, it was originally a natural fireplace – converted to gas – then re-converted back to natural. I have burned natural wood, but can’t stand having my family room smelling of smoke. Because of this, I’ve decided to go back to gas. I’m almost done with the conversion – but wonder what you might suggest for a “draft stopper” – since I don’t want to buy a new screen cover. I like the “open look” of the brink fireplace – and would like to keep that look as a focal point in the family room, so I’m looking for a draft solution for when it’s not in use, of course, still keeping the open look. What you you suggest?

    Thanks for your help!


  8. I believe the term is “flame impingement” that you are mentioning. More often than not the logs are not positioned or stacked as the manufacture designed. I would suggest going online and searching for that particular Gas log manufacture manufacture make and model. You will be looking for a picture diagram of the log positioning. I personally don’t think that your glowing embers are contributing to the soot problem. That is providing that any of the ember materials are not blocking on of those very small orifice openings. These must be opened to provide the gas for the flame.
    Burn Safe and Warm,
    Clay Lamb

  9. I recently updated my furnace with A 95% efficient which exhausts through the wall leaving my hot water heater the only appliance vented in my chimney with a 8×12” flue. I noticed that when the hot water heater is not burning, there is a small amount of back draft of coming out of the water heater bonnet, enough to blow out a butane lighter. When the water heater burner ignites there is good draft and the butane lighter flame is sucked up the flue. Is there any way to correct this problem? Add more height to the chimney? Is there a different type chimney cap to use to prevent a downdraft?

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.