How to properly make a chimney for a gas boiler

For comfort, energy efficiency, and safety, your home must have adequate insulation and heating. Having a well-designed chimney for your gas boiler is an essential part of this. Your chimney acts as your boiler’s exhaust system, ensuring that dangerous gases are safely expelled from your house and that there is enough airflow to facilitate combustion. This post will go over the essential procedures and factors to take into account when building a chimney that satisfies safety regulations and maximizes the efficiency of your gas boiler.

It’s critical to comprehend the function of a chimney in relation to a gas boiler before delving into the particulars of chimney construction. When fuel is burned in gas boilers to produce heat, combustion gases are produced. Carbon monoxide and other potentially dangerous substances found in these gases must be safely vented outside of the house. In addition to facilitating the effective expulsion of these gases, a well-designed chimney guards against backdrafts, which may cause carbon monoxide poisoning or other indoor air pollution.

Planning the construction of a chimney for your gas boiler requires consideration of a number of factors. Respect for local building codes and regulations comes first. The minimum specifications for chimney height, material, insulation, and distance from combustible materials are set forth in these codes. In addition to facing penalties, breaking these rules may jeopardize the security of your house and its occupants.

The particular needs of your gas boiler should also be taken into account when designing the chimney. The size and design of the chimney may change depending on the exhaust temperature and airflow requirements of different boilers. Referring to the manufacturer’s specifications and recommendations is crucial in order to guarantee compatibility and best performance.

Adequate insulation is a crucial component of chimney construction. Chimney insulation reduces condensation, helps to maintain ideal exhaust temperatures, and boosts overall performance. Insulation materials that offer thermal resistance without adding extra weight or bulk to the chimney structure, like mineral wool or ceramic fiber blankets, are frequently used for this purpose.

Options of chimneys for a country house

For the purpose of eliminating relatively low-temperature combustion products (up to 120 °C) released by gas boilers, appropriate for the following kinds of chimneys:

• three-layer modular sandwich made of stainless steel with non-combustible insulation – basalt wool;
• channel made of iron or asbestos-cement pipes, protected by thermal insulation;
• ceramic insulated systems of the Schiedel type;
• brick block with a stainless steel pipe insert, covered from the outside with thermal insulation material;
• the same, with an internal polymer sleeve of FuranFlex type.

Note: Coaxial chimneys are required for gas boilers with closed combustion chambers (supercharged or turbocharged models excluded). It’s actually a double-walled metal pipe that can release smoke outdoors while also drawing in combustion air from the street.

Let me explain why it is not possible to install a standard steel pipe that connects to a gas boiler or to construct a traditional brick chimney. Water vapor is a waste gas that is produced when hydrocarbons burn. Following moisture’s contact with cold walls, condensation forms, and the following sequence of events occurs:

1. Due to the numerous pores, water penetrates into the building material. In metal flue pipes, condensation flows down the walls.
2. Since gas boilers and other boilers with high efficiency (solar and liquefied propane) operate intermittently, frost has time to catch the moisture, turning it into ice.
3. Ice pellets, increasing in size, hollow out the brick inside and out, gradually destroying the chimney.
4. For the same reason, the walls of an uninsulated steel gas duct closer to the casing become covered with ice. Reduces the passage diameter of the channel.

As a point of reference. Single-wall metal chimney joints get unsightly, unclean smudges from the outside world.

Selection recommendations

We advise using sandwich pipes made of stainless steel because we originally agreed to install a low-cost, do-it-yourself version of the chimney in a private residence. The following issues arise when installing different kinds of pipes:

1. Asbestos and thick-walled steel pipes are heavy, which complicates the conduct of work. In addition, the outer part will have to be covered with insulation and sheet metal. The cost and duration of construction will definitely exceed the sandwich assembly.
2. Ceramic flues for gas boilers – the best choice if the builder has the means. Schiedel UNI systems are reliable and durable, but they are too expensive for the average homeowner to afford.
3. Stainless and polymer inserts are used for reconstruction – gilzovanie existing brick channels, erected earlier according to old projects. It is unprofitable and pointless to build such a structure on purpose.

A sandwich chimney made completely of stainless steel is preferable since it will last longer and still look nice. Choose a modular system with galvanized metal lining if the project’s budget is extremely tight; the structure will last for at least 20 years.

An additional pipe can be used to organize the supply of outdoor air for a turbine gas boiler when it is connected to a typical vertical chimney. When the private residence already has a gas duct leading to the roof, the technical solution ought to be put into practice. In other situations, the most practical and accurate solution is to install a coaxial pipe, as seen in the picture.

The final and least expensive method of building a chimney is noteworthy: using your hands, construct a sandwich for a gas boiler. We take a stainless steel pipe, wrap it in the appropriate thickness of basalt wool, and then coat it with roofing galvanizing. The following video illustrates this solution’s practical application:

Chimney of solid fuel boiler

Hotter gases are released during the coal and wood heating units’ modes of operation. Condensate essentially never freezes, the temperature of combustion products reaches 200 °C and above, and the flue channel is fully heated. But when soot accumulates on the interior walls, it is replaced by yet another unseen foe. It ignites periodically, and the chimney can heat up to 400–600 degrees Celsius as a result.

The following kinds of chimneys are appropriate for solid fuel boilers:

• three-layer stainless steel (sandwich);
• single-wall stainless steel or thick-walled (3 mm) black steel pipe;
• ceramic.

It should be noted that installing regular stainless steel pipe inside a home without basalt fiber fire protection is not advised. Click this link to learn more about installing wood heaters.

It is not recommended to install asbestos pipes on TT boilers, stoves, or fireplaces because the high temperature can cause them to crack. It is preferable to line the brick channel with a stainless insert because a basic brick channel will function but become clogged with soot due to its roughness. FuranFlex’s polymer sleeves won’t break because its maximum operating temperature is only 250 °C.

Design and procurement of materials

Take a few preparatory steps in order to accurately choose the modular chimney’s details and determine how much material will be needed:

1. Study the requirements for gas boiler chimney flues.
2. Determine the method of laying, the diameter of the channel and the thickness of thermal insulation.
3. Draw a diagram and make a list of materials.

As a point of reference. Gas ducts and ventilation exhaust pipes are typically installed first when installing a heat source in a country home. In the second turn, the heat generator is installed in the boiler room and connected to the heating system.

Some homeowners might be confused by the clever terms "calculation" and "project" in the list above. These steps are actually not that difficult. We will provide the standards here so that you won’t need to search for them on the chimney device.

Regulatory requirements for chimney stacks

For the straightforward reason that if the gas duct is installed improperly, the fuel supplier company will not accept the gas boiler for operation and will not connect it to the mains, the building codes and regulations (SNiP) instructions must be followed. The following criteria must be met:

1. The total length of horizontal sections preceding the vertical flue shaft is a maximum of 3 meters. A slight slope towards the heating unit should be provided (1-3°).
2. It is allowed to deviate the vertical channel by 1 meter to the side in order to bypass the roof overhang. The slope of the bypass section from the chimney axis is 30°.
3. The number of turns of the pipe is limited – no more than 3. Elbows around the roof overhang are not taken into account.
4. The passage cross-section of the outlet duct may not be smaller than the size of the corresponding branch pipe of the heat generator.
5. Floor-standing and wall-mounted boilers equipped with a top spigot are connected by a vertical section of at least 25 cm long.
6. The distance of the uninsulated gas duct from the combustible building structures of a wooden house is at least 0.5 m, from non-combustible – 10 cm.
7. The intersection of wooden walls or floors (cutting) is made with an interval of 38 cm between the combustible structure and the inner wall of the chimney of the sandwich type. It is not allowed to connect sections inside the wall.
8. Diverting pipe for a gas boiler must be raised to a certain height, so that the header does not appear in the zone of wind support, which significantly reduces the strength of the natural draught. The elevation depends on the distance to the ridge and is determined according to the scheme.

A condensate collector with a discharge connection and a cleaning hatch (revision) are located in the lower blind portion of the vertical section. The boiler pipe segment can be made single-walled, but the sandwich needs to go out onto the street or into the adjacent attic space.

Vital. When counting from the gas burner or solid fuel boiler grate, the minimum height for the chimney construction should be 6 meters.

Determine the diameter and method of laying

The answer to the first query can be found in the chimney channel requirements. Take a look at the passport heat generator’s connection dimensions and choose a sandwich chimney with an outlet pipe diameter that is either the same or greater.

The second query concerns how to select the thermal insulation sandwich thickness, given that the manufacturer provides a minimum of two options: 5 and 10 cm. An insulation thickness of 50 mm is adequate to prevent severe condensation and freezing of the chimney that is connected to the gas boiler. It is recommended to use 10 cm insulation in northern areas where winter temperatures can drop below freezing.

The final step is to select which of the two possible layout options to use:

• The horizontal section can be led outside through the wall and connected to a vertical chimney;
• It is not necessary to pass a vertical pipe through the floor, attic and roof, i.e. to lay a smoke exhaust duct inside the house.

Note: While both versions can be used to install coaxial gas ducts, the first one is typically implemented with an outer wall passage.

The easiest and least expensive method is to lay along the street’s shortest path and raise the pipe along the wall. In the first variant, just one structure needs to be crossed; in the second, at least two structures. additionally caulking the roof covering’s intersection with the chimney.

A healthy pipe will unavoidably pass through a house with two floors or a mansard roof, taking up valuable space, so try to avoid laying inside. If mounting the chimney from the outside is not feasible, create a cross-sectional diagram of the building and the chimney that passes through it.

Make a list of parts according to the diagram

Installing an attached chimney linked to a gas or solid fuel boiler requires the following modular sandwich components:

• Tee with 89° spigot for connecting the horizontal section to the vertical section;
• T-piece with inspection hatch;
• section with condensate collector;
• section of single-wall pipe and coupling for connecting the heat generator;
• transition ordinary pipe – sandwich;
• straight sections – the number and length are selected according to the length of the gas duct;
• 2 30° elbows are needed to bypass the roof overhang;
• a nozzle-shaped top cap to protect the insulation of the last section from precipitation.

Important point. It is not permitted to install decorative canopies or fungi on the chimney of a gas boiler. The passage section will narrow and the casing will freeze during the impact frost period, endangering the lives of the occupants.

To support the weight of the mounted structure, wall clamps with brackets and a support platform are required from the fastener parts. In addition, you will require prefabricated floor penetrations, a roof sealing cap (also called a master flush or roof cap), and 90° elbows to mount the flue pipe in the boiler room if you intend to install the gas duct inside the structure.

In crafting a chimney for your gas boiler, ensuring proper design and installation is crucial for safety and efficiency. A well-constructed chimney facilitates the smooth expulsion of combustion byproducts, preventing hazardous gases like carbon monoxide from seeping into your home. Start by determining the appropriate chimney size and height based on your boiler"s specifications and local building codes. Opt for high-quality materials resistant to corrosion and heat, such as stainless steel or ceramic. Proper positioning of the chimney, including its distance from combustible materials and nearby structures, is essential. Additionally, ensure thorough insulation to prevent heat loss and condensation buildup, which can damage the chimney over time. Regular inspection and maintenance are key to keeping your chimney functioning optimally and your home safe. By following these steps, you can create a chimney that promotes efficient operation and protects your household.

Installing the sandwich chimney

The attached structure’s initial installation step involves drilling a hole in the exterior wall and getting ready to install the horizontal section. When designing an opening in a combustible-material house, consideration is given to the installation of the passage unit’s flange and the fire clearance (38 cm between the inner pipe of the sandwich and the wooden wall’s edge), as seen in the attached photo.

Note: Installing a fire protection section is not required in non-combustible constructions consisting of bricks and foam blocks. After inserting the gas duct section and a metal sleeve into the opening, non-combustible material is used to seal the gap.

The following is the order in which the modular sandwich installation and gas boiler connection are completed:

1. Assemble the lower part of the attached chimney, including 2 tees and condensate drainage section. Join the horizontal section going into the opening.
2. Try the assembly on the wall and determine where to install the support pad. Fasten it and install the lower part by inserting the pipe into the wall. Maintain vertical alignment by checking the position of the assembly with a construction level.
3. Having fixed the lower part of the gas duct, mount the vertical section. Straight sections connect in such a way that the shell of the upper put on the lower, and the gas pipe, on the contrary, inserted inside (assembly "on the condensate").
4. Fastening of the wall chimney channel should be carried out at an interval of not more than 2.5 м. The brackets must not fall on the joints of the sections.
5. Lay the horizontal section of the sandwich pipe up to the gas boiler and put on the adapter. Fasten the chimney with clamps to the building structures with a maximum spacing of 1.5 м.
6. Connect the heat generator to the chimney with a piece of single-wall stainless steel pipe.

Remind yourself. Install metal flanges on both sides and use basalt fiber to seal the opening in a wooden house between the wall ends and the crossing pipe.

Sealant does not need to be applied to the joints; instead, straight sections are simply inserted into each other and secured with clamps. Shorten the lower end of the section where the insulation is flush with the metal linings if trimming is required. The upper portion of the flue duct has a protective cone installed.

The method for laying the chimney channel within a building is the same; the only difference is that you have to pass through the structure two or even three times. Everywhere, the same guidelines for sectioning are adhered to at the junction of combustible floors and walls. Lastly, as demonstrated in the video, the roof at the pipe passageway needs to be carefully sealed.

Step	Description
Gather Materials	Get all the necessary materials for the chimney, like stainless steel piping, elbows, brackets, and flashing.
Plan Route	Determine the best path for the chimney to run from the boiler through the house and outside. Consider safety regulations and clearances.
Install Support	Mount brackets to support the chimney piping securely along its route, ensuring it"s stable and won"t shift.
Connect Pipes	Connect the stainless steel piping together with elbows as needed to form a continuous pathway for exhaust gases.
Seal Joints	Use high-temperature sealant to seal any joints or connections in the chimney piping to prevent leaks of dangerous gases.
Add Flashing	Install flashing where the chimney exits the roof to provide a weatherproof seal and prevent water from entering the house.

The design of the chimney must be carefully considered in order to guarantee the safe and effective operation of your gas boiler. For combustion gases to be effectively vented and dangerous emissions to be kept out of your home, proper chimney construction is essential. You can design a chimney system that complies with regulations and supports the best boiler performance by adhering to certain guidelines.

First and foremost, take into account the chimney’s height and dimensions in relation to the location and capacity of the boiler. An inadequate draft from a small or short chimney can cause poor combustion and possible safety risks like carbon monoxide buildup. On the other hand, an oversized chimney may permit flue gases to cool too much, raising the possibility of condensation and corrosion. Achieving the proper balance is crucial for effective functioning.

Next, select building materials for your chimney that are appropriate and resistant to weather exposure and combustion byproduct corrosiveness. Common materials include masonry, galvanized steel, and stainless steel, each with pros and cons. In order to keep draft stability and stop heat loss, proper sealing and insulation are also essential, particularly in colder climates.

To further reduce the risk of a fire, make sure there is enough space between the chimney and combustible objects. To prevent possible safety concerns, adherence to manufacturer recommendations and local building codes is crucial. Maintaining the efficiency and longevity of the chimney system requires routine inspections and maintenance, which includes clearing out any debris or creosote buildup.

Lastly, for advice on chimney design and installation, think about speaking with certified experts like HVAC technicians or chimney sweeps. Their knowledge can assist in addressing particular needs and guaranteeing adherence to pertinent laws. Investing in a well-designed chimney improves your gas boiler’s efficiency while also adding to the general security and comfort of your house.

Video on the topic

Coaxial chimney for gas boiler

Gas boiler connected to the chimney, and you are told to redo and give a prescription!!!

Five mistakes when installing a chimney with your own hands or how to assemble a chimney for a boiler from a sandwich pipe?