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How To Tell If A Chimney Is Structural: Find Out!

Whether a chimney is structural or not is a major concern of the majority. As the defragment of chimneys might be vulnerable for building infrastructure. 

How to tell if a chimney is structural?

Structural chimneys are primarily made of silicate bricks. It has a strong upward draft that draws out the by-product of burning fuel. And these gases are emitted by a part called flue that hides behind masonry. In addition, a chimney pot is located on the top of the chimney cap. It also includes smoke, firebox, and base assembly. 

Haven’t got your answers? Don’t worry. We presented a complete guideline to answer all of your queries. 

Stay tuned with our tutorial. Sit tight to explore!

Factors to Determine A Chimney to Be Structural

We know there are different types of chimneys used in our houses. But not all of those are a structural part of the houses. Two types named masonry and prefabricated chimneys are supposed to be the structural ones.

Why are the others not structural? In this very section, we’ll explore the factors on how to identify which chimneys are structural. There are some common traits to identify a structural chimney.

Factor 1: Chimney Pot

Commonly most of the chimneys’ come with a concrete cap. It’s an extension that is found on top of the chimney’s smokestack. 

In the case of the structural chimneys, they come with chimney pots. Now chimney pots are a bit different than the caps as the name suggests. They are commonly found on the topmost section of the chimney smokestack.

Often they’re spotted over the chimney caps with a little vertical extension. These pots prolong the smokestack to yield a better draft for combustion.

Factor 2: Chimney Draft

What does the chimney draft mean? While a chimney is filled with gases, it starts to rise. It’s because the inner gas is lighter than the outside air.

At that time the hot gases create a pressure divergence which is called chimney draft. It instigates the combustion air into the fireplace and exhales the gas outside.  

As we’ve known what chimney draft is, we can proceed into details. 

The draft of the chimney is associated with the structural condition of the brick chimney.  As a result, a low stream of stack air contributes to a drop in the temperature. 

Here temperature denotes the combustion gases temperature. And, that warmth in turn contributes to the formation of more condensates.

Being a structural part of a building, chimney drafts decay with the compactness of the building. The long-term natural functioning of the chimney crumbles the chimney draft. 

If a building is being equipped with forced ventilation, you need to be careful. Otherwise, the draft will be distorted while repairing the façades. Also replacing the openings will affect the draft very badly. 

To that end, it’s advisable to leave adjustable vents on the exterior wall. It’ll allow the oxygen necessary for burning to enter the building. In case you were looking for some, we have jotted down the best pick for you-

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Factor 3: Flue Gases’ Temperature

The structural chimneys are constructed to maintain the temperature within 100 °C. Their structure must ensure that the temperature doesn’t fall below the standard limit. 

The maintenance of temperature depends on the type of fuel being used. If Liquid fuel like oil or gas is burnt then temp remains below 100˚C. It’s because of their less combustion ability concerning that of wood. 

Commonly the gas fireplace is used to heat the house. But nowadays a number of good alternatives are available in the market. 

They are very cost-efficient and use less wood to burn. And therefore, you can convert a gas fireplace with a pellet stove. It’ll surely save your money and ensure better performance than gas ones. 

We should consider the low temperature of the combustion gases. Also, consider the large quantity of water they contain in it. The liquid contained in the flue gas condenses in the stack. Here stack means the cold interior surface of the flue.

Condensate corrodes and starts to actively interfere with the operation of the smoke channel. Therefore, all oil boiler manufacturers recommend using acid-resistant pipes (stainless steel or ceramic) in the furnace stacks.

Factor 4: Handling Temperature Fluctuation

Due to massive temperature fluctuation in winter, structural chimneys are often distorted. 

By warming a building in winter, the huge temperature difference creates a new scenario. Here, liquid from the interior of the stack is pressed outwards on a cooler surface. 

For the stone and a 120 mm thick joint, this drying cycle takes 3 to 6 months. It builds the bundling of moisture within the stack.

The cold night rapidly cools the chimney after the end of the furnace. Inside the stone, ice crystals are formed as well. As the ice develops, the volume increases and, in turn, creates internal constraints.

Gas furnace vents are mostly used to heat our houses. On such nights these vents might also be covered with ice flakes. 

Because of internal stresses in a silicate brick, the surface is disfigured. Also cracking of the entire stone occurs at a thickness of 120 mm. It’s therefore recommended to place the fireplace in our climate zone no later than early September.

This plot is accustomed to only structural chimneys. So you can easily match your chimney type whether it’s structural or not.

Factor 5: Heating and Building Blocks of Chimneys

A fireplace is commonly known as a chimney breast. However, only dry woods are recommended to put on the furnace. The moisture content shouldn’t cross over 20% at all.

The structural chimneys use silicate bricks for their interior. An acid-resistant corrosion-resistant stainless steel nozzle is installed in the conduit. 

The coating of the silicon pipe is laid on a solid cement mortar (T100/ 300). The end of the chimney is protected by a galvanized or painted metal cap.

In this way, these factors will define your chimney to be structural. 

Reasons to Reconstruct the Chimneys

If you have any chimney system you might have odd experiences. You should know why that happens. And the possible cautions and consequences. It’ll help you to stay safe and free from anxiety. 

Whatever it is, let’s jump into the discussion. We’ll first try to understand why we need to reconstruct the chimneys.

There are multiple reasons to reconstruct or renovate the structural chimneys. Those reasons are-

Reason 1: Soot Formation

We found these nasty spots mostly in brick chimneys. Irregular cleaning or overloaded fuel cause this to happen. Also, the incorrect operation to the furnace with airside closed or residual moisturizer makes such spots.

You should clean the firebox Assembly and the flue regularly. It’ll keep your system free from unwanted soot formation. 

Reason 2: Moorish Chimney

If your chimney starts to tilt on one side then it’s a concern. In that case, a masonry expert should be called to get it in the correct position. 

You should solve the issue as soon as possible. Otherwise, it might be called unwanted trouble that takes too long to resolve. 

Reason 3: Chimney Fire Outbreak 

If you ever noticed any small chimney fire then it’s a matter to worry about. There may be cracks or debris in your chimney system. Or might be a double-sided fireplace issue. In such cases, it might need to rebuild the whole chimney system.

It might have a small fire inside the system. But remember though the fire is small it’s inside the chimney. So chimneys’ fire can melt the mortars and create deep cracks on the bricks. 

Reason 4: Water Leakage

Sometimes we might notice some droplets of water around the chimneys. Maybe your chimney system has been damaged. And, water is leaking into your house through the chimneys’ duct. 

If this problem is not addressed earlier, your entire chimney system might break into pieces. Then it’ll require a full rebuild of your system. So better to check it carefully and solve your issue before it collapses. 

These are the common reasons to reconstruct the chimneys. Try to follow the points that we’ve discussed earlier. Otherwise, you might end up having a replacement or reconstruction in your chimneys. 


Question: What’s the distance of the chimney from the base of the fireplace?

Answer: 15 feet. The top of the chimney should be at least fifteen feet long from the firebox assembly. It’s the standard measurement for structural chimneys. 

Question: Is chimney breast structural?

Answer: Yes. They are an indispensable part of the building structure. If it’s removed then additional support is needed to hold the masonry above. 

Question: Do metal chimneys belong to structural chimneys?

Answer: No. This type of chimney is not structured like masonry or prefabricated chimneys. They are coated with metal sheets and hang outside of the house. 


We’ve come to the end of our discussion. By now you might understand how to tell if a chimney is structural or not. We hope our detailed guidelines have all possible ways to detect a structural chimney. 

Wish you very good luck!