How tall chimney

The internal area where the smoke and gases flow is called the flue and is often the primary area of focus for chimney sweeps to clean. While not found in older chimneys, this flue has been required in all homes past the s as it protects the chimney itself from the corrosive elements that come from smoke and gas.

The flue and chimney can be made up of a myriad of different items with tile, concrete, and metal being the most common. The primary mechanism of use relies on the relative pressure from the inside to outside. As imagined, the temperature of the air inside the chimney is much higher than the surrounding air. This increased temperature results in a higher degree of energy adding to the air making it much less dense than the cooler air outside of the house. This can create a suction when the smoke is pulled out of a home by natural draft.

The overall height of the chimney stack influences the amount of draft created — with the higher the stack typically translating to more draft.

As imagined, if a chimney is too short it will suffer from poor drafting problems — this is a result of not enough internal pressure being built up to expel it to the outside. Chimneys that are excessively tall can have some issues as well though. This can create a negative pressure inside of the smokestack that pushes smoke and other gases back into the home. In order to get a proper height, many engineers have created a formula to accurately create the correct size chimney.

Knowing the molecular weight of the gas being emitted and assuming things like heat loss and friction are low, there are only a few other elements that need to be known. While outside the scope of this guide, things like gravitational acceleration, average temperature inside the chimney, the height of the chimney, among other factors must be calculated into this formula.

For the layman, there are some rules of thumb that can be employed to figure out an extremely close approximation on how tall a chimney needs to be. The air space around chimneys must be maintained or they will overheat. Please do not blow insulation into the cavity.

If you want to insulate, only put it between studs. Also, insulation and air barriers in chases must be contained by sheathing to prevent them from heating up and falling against the chimney. A number of things affect how strong cold backdrafting can be, and how big a problem it is, such as:. The really bad thing about outside chimneys is that the remedial measures are either ineffective or unappealing or expensive or all three, which is why we tend to be strident about not installing chimneys outside in the first place.

Insulating the chase might help some, but a large component of heat loss from typical chases is from leakage, so sealing it [including top and bottom] is at least as important as insulation. The only way to really fix an outside chimney is to trick it into thinking it is inside. That would mean a chase that is the same temperature inside as the house is so the chimney stays warm enough to compete with house stack effect.

With a really well sealed and insulated chase, you could vent it into the house, with a couple of passive vents at top and bottom of each storey, so that a convection current would keep the inside of the chase nearly as warm as the house. That strategy is the only one sure to work, and then only if it is done well. On the other hand, if your climate is reasonably mild and your house is reasonably short and if its leaks are relatively low and you keep fires burning most of the winter and you burn the wood bright, hot and clean, you might never have a problem with cold backdrafting.

We installed a new woodstove with an existing chimney when we moved into our house three years ago. Last spring and this winter, we have been having problems with smoke coming into the house through the stovepipe joint where it enters the ceiling. When it first happened last spring, we thought it was possibly because of a pressure inversion.

This winter, however, we seem to have a smoky house any time there is a wind. Our chimney is straight, inside in a one story addition to a one and one half story house.

Do you have any diagnosis for the problem, where we can get help, and how we can fix it? We didn't have this problem the first winter we were here. Problems of this kind are so complex that I could spend a long time writing to you about possible contributing factors.

I can't do that. But here are a few ideas. A chimney installed in a single storey section of a two storey house has to compete as a stack with the house, especially when no fire burns or when chimney temperatures are low like when the fire smolders. This may not be the main cause, but it weakens the chimneys ability to flow air and gas up under all conditions. You need to pay attention to which wind direction leads to the problem. If spillage happens when wind blows from the single storey side, you need to look for leaks on the downwind side of the house on the two storey side, especially high level leaks like open second floor bedroom windows or a leaky attic hatch.

This situation can depressurize the house and suck flue gases down the chimney into the room. Smoldering fires are a key cause of this type of failure. Make sure that you burn small, hot fires and don't let the fire smolder. The wood should be flaming until it is reduced to charcoal. If there is no cap on the chimney, get one; open chimneys are extremely vulnerable to adverse winds. Raising the chimney might help to get the top of it up out of a zone of positive pressure caused by a wind effect.

Ideally you could contract with someone who can come to your house and diagnose this, but such people are hard to find. Check first with local chimney sweeps or long-time stove and fireplace retailers.

What options are available for fireplace flue repair? We are working on a project where there are two existing fireplaces, roughly years old. The owner would like the fireplaces restored. Can stainless steel liners be used on wood burning fireplaces? Yes they can, but it is not an elegant solution because the connection above the throat and damper are difficult to do and rarely done well.

Since we at woodheat. In this case the liner is sized to the insert, not to the fireplace, and the connections can be secure and permanent. An additional benefit of an insert is that it would improve resistance to smoke spillage into the room and reduce outdoor air pollution from the fireplace.

This is the only environmentally responsible solution, in our opinion. If your client insists on retaining the conventional fireplace for historical or nostalgic reasons, a far better solution than stainless steel is a solid-set poured-in-place lining system. This insulating cementatious material greatly improves the structural integrity of the chimney and improves performance by insulating it. You need to find a supplier of SolidFlue, Arens, Golden Flue, Supaflue and there may be a couple of others that I can't think of at the moment.

Chimneys sweeps can usually tell you if there is a local supplier. I bought an old house in Philadelphia. The heating system is gas, hot air. There are two chimneys. One vents the heating system and air conditioning; that one is in the living room. The other vents the hot water heater. I would like to add a fireplace in the living room.

I would prefer wood. It would need to be very small, as the living room is 14 X Is there some way to utilize the chimney that vents the heating system?

If not, how expensive would it be to install a new chimney for a wood burning fireplace ball park figure is OK. The house is two stories and very small. Am I better off with a direct vent gas fireplace? Any advice would be greatly appreciated!!! There are many factory-built fireplaces on the market of all shapes and sizes. You need to visit a few fireplace retailers, see what they have and what they have to say. We are not the right people to ask about gas fireplaces.

Since most everyone else will advise you to go gas, including most fireplace retailers, I will suggest that if you want a real fire, the only option is wood.

Wood Heat Wisdom. View All. Torri Hi Torri, Yes there are some important issues to deal with. John Boosting efficiency with a flue pipe mounted heat reclaimer?

Kevin Hi Kevin, Retrofit flue pipe mounted heat reclaimers used to be popular until it was learned that all they do is plug up with creosote. John BBQ starter as a chimney primer?

Rich p. Hi Rich, I suspect an electric BBQ lighter might work, but it is rather energy intensive and maybe time consuming. John Chimney Failure I have a franklin stove in my basement, which is in the new addition of my home. Any ideas will be much appreciated Thanks, Steve Hi Steve, You are suffering from a classic type of chimney failure. John Fireplace Chimney Problem I have a problem with the chimney for my year-old split-level house in Toronto, Canada.

Sorry for all the questions but I hope you can help. Thanks, Darren Hi Darren, This chimney has both of the worst possible characteristics. John Outside chimney causes problem? The flue is outside. It gets to deg F here sometimes. Any thoughts, help, leads? John Chimney Height and Draft Could you tell me the right way to draft a chimney? Thanks, Keith Hi Keith, The chimney should extend at least 3 feet above the roof surface it penetrates and 2 feet higher than any roofline or other obstacle within a horizontal distance of 10 feet.

Two things determine chimney draft: 1. John Proper Height of Flue We have inherited a good woodburning freestanding fireplace to install in a section of our home but we don't know how high the flue should be. Your help will be appreciated Felicity Hi Felicity, First, the top of the chimney must be at least 1 metre above roof level to prevent excessive turbulence.

John Shared Flue? Thanks, Paul Hi Paul, In a word, no. John Suppliers of Chimneys We're interested in installing a woodstove and are wondering what places online, presumably are best for us to learn about and purchase the stove pipes we will need. Thanks, Lisa Lisa, When you say stove pipes I assume you mean chimney, as distinct from the flue pipes that run between the appliance flue collar and the chimney.

Price should not be your first concern — safety is what is important. Thank You, Scott Scott, The plan sounds hazardous to me. However, planning the installation is very important. Don't worry though, we're here to help you through it! Many factors must be taken into consideration to have a safe and proper U. One of the most important aspects of the planning process is installing the proper amount of chimney pipe above the roof.

If you've been researching Class A chimney pipes , you've probably heard of the foot rule numerous times. This rule refers to the proper height of the chimney pipe above the roof. Explained, the chimney pipe must be a minimum of three feet above the roof but also two feet taller than anything within ten feet. The portion of the rule stating the pipe needs to be 2 feet above anything within 10 feet is where most people get confused. Most people think of that in terms of trees, satellites, or other parts of the home, which are all accurate, but neglect to consider the roof itself.

The higher the roof pitch is, the closer the roof will be to the pipe where it penetrates the roof. This doesn't necessarily mean the pipe must be above the tallest part of the roof, which is known as the ridge.

But, the pipe will require a 10' horizontal clearance from the roof. They intend to make sure that the chimney draws properly and that a fire hazard does not occur.

If, however, the manufacturer of a factory-built fireplace unit, wood stove , or other appliance has other specifications, these must be followed. Any peak that is within 10 feet of the chimney can compete with the chimney. This can cause draft problems. This is why the rule calls for the chimney to extend 2 feet above any structure within 10 feet of the chimney. If your home is at a particularly high altitude, I recommend consulting a professional in your area when it comes to these particular specifications.