How high should the chimney be above the roof and ridge

In private houses and cottages, heating systems use boilers and stoves that run on one or another type of fuel. The combustion process produces smoke, carbon monoxide. It must be diverted outside the room. This function is performed by the chimney. The height of the chimney above the roof plays an important role, because if the standards are not observed, the system becomes ineffective, fuel consumption increases, smoke is drawn back into the room, and fire safety decreases.

The main criteria and requirements for the design of a chimney

The gas generated during the combustion of fuel has a significant effect on the temperature in the house. By correctly designing the chimney, you can use the thermal energy of the flue gases more efficiently. In addition, the design features of the chimney significantly affect the efficiency of heating devices and fuel consumption.

The effective operation of the chimney and compliance with fire safety standards are ensured even in the course of drawing up a project, a diagram. The following criteria are taken into account:

• Material. Must be able to withstand the temperature of the exhaust gases on a case-by-case basis. The residual temperature is determined by the type of fuel.
• The parameters of the section of the chimney duct and its height must comply with the technical requirements. If the necessary calculations are not made, the operation of the heating unit will be incorrect.
• Ventilation ducts for heaters, fireplaces, stoves are combined, because construction of separate canals is impractical. This requires additional calculations and measurements.

The height of the chimney is determined by:

• location relative to the ridge;
• wind rose;
• angle of inclination of the roof;
• average annual snow height;
• wind speed;
• the presence of obstacles blocking the free movement of air: trees, buildings.

In addition, additional recommendations should be followed:

• The height of the chimney from the lowest point to the outlet is at least 5 m.
• If tall houses and a boiler are built nearby, the stove is fired with wood, the pipe rises at least to the level of the roof of neighboring buildings.
• The height of the ventilation ducts, which are located close to the chimney, must be equal to the height of the chimney.
• You should not lead the chimney channel into the joints of the roof slopes - valleys, in winter snow will accumulate here.

According to the regulations, it is not recommended to rigidly connect the chimney structure with the rafter system and the roof in order to avoid damage when exposed to the pipe.

The nuances of choosing a chimney

It is necessary to calculate the height of the chimney and determine the size of its section at a certain position of the pipe. With an increase in the height and a decrease in the cross-section, the thrust increases, and vice versa: with a decrease in the height and a decrease in the cross-section, the thrust decreases. It is necessary to choose such a ratio that the thrust was optimal - the efficiency did not decrease and carbon monoxide gases were removed.

Cylindrical channels are better suited for the cross-sectional shape. They warm up evenly, therefore they are most conducive to the uniform movement of fuel gases. If the chimney is rectangular, it warms up and expands unevenly, because of this, it gradually collapses.

Unequal heating of different parts of the surface has a negative effect on the process of natural traction.For a chimney that removes combustion products from a stove or fireplace, this is permissible. The upward flow moves in a spiral, vortices arise, which contributes to a more complete use of thermal energy. However, more soot and burning is generated. When choosing a chimney for a gas or solid fuel boiler, it is definitely worth choosing a cylindrical one.

The material for making the chimney matters. A brick mine is ideal when using solid fuels such as firewood. But this is not the best option when heating with a gas boiler.

Types and characteristics of chimneys

Chimneys made of different materials will differ in their characteristics.

Asbestos-cement pipes are traditionally used for arranging chimneys and are still considered the most budgetary option, but far from the best. Chimneys made entirely of asbestos are unsafe to operate:

• when heated, carcinogens are released;
• the material cracks and breaks down at temperatures above 300 ° C.

It is permissible to make from asbestos-cement pipes only areas remote from the heat source. But when assembling, it is difficult to achieve tightness, including when using other materials. Asbestos has a porous and rough structure, so the surface quickly becomes overgrown with soot and absorbs condensate, which destroys the pipe and reduces draft.

Brick chimneys are a classic. Advantages balance disadvantages. Of the advantages, it is noted:

• impressive service life - more than 50 years;
• fire resistance;
• aesthetic appearance.

Disadvantages:

• complex assembly and maintenance;
• rough surface that accumulates soot;
• significant weight of the structure;
• susceptibility to acidic environments.

Solid metal chimneys are made of stainless steel. During their installation, there are no significant difficulties. They are characterized by numerous advantages:

• light weight;
• anti-corrosion properties;
• resistance to high temperatures (up to 500-700 ° C);
• smooth inner channel;
• long service life (15 years or more);
• prevent the formation of condensation.

There are also disadvantages: limited use due to thin walls. They can only be used as a liner in a brick shaft or indoors. In order to expand the scope of use, all-metal chimneys are insulated.

The modular chimney is devoid of almost all the disadvantages typical of other types of chimneys and is versatile. It is a double-circuit sandwich pipe with a layer of mineral wool 2-6 cm thick. Its installation is as simple as possible, due to the possibility of assembling the channel from a variety of shaped elements.

General Provisions

The location of the highest point of the chimney is of great importance for fire safety and the efficiency of the heating system. Natural thrust is formed according to the laws of physics: warm air tends upward, and the vacant space is occupied by a new portion, since the vacuum is instantly filled. The more heated air, the more intense the draft, which is interconnected with the height of the chimney and its cross section. The purpose of all calculations and recommendations is to achieve such an upward flow rate so that heat loss is minimal, but at the same time, the combustion products do not have time to get into the room. Too much draft is not desirable, because heat will not be transferred to the air masses, and more fuel will have to be burned to maintain a comfortable temperature in the house.

Another aspect must be taken into account: an excessively high chimney will negatively affect the system for removing fuel combustion products, although it would be logical to assume that the higher the chimney, the greater the draft.This is true, but the stream, rising higher and higher, gradually cools down, and the cold air tends downward. At a certain moment, an air lock of cold gas forms, which presses from top to bottom on the ascending warm stream and prevents it from rising higher - the thrust comes to naught. In addition, the situation is aggravated by the fact that when the gas cools down, condensate precipitates. It further reduces cravings.

It is advisable to place the chimney from the ridge at a distance of at least 50 cm and not more than 150 cm. The height of the chimney above the ridge is at least 50 cm. This placement is successful for practical reasons:

• at this level, snow accumulates in a smaller amount, therefore, the risk of leaks at the junctions is reduced;
• materials are saved during construction.

You can bring the pipe outside, removing it 1.5-3 m from the ridge, then the height of the chimney should be: maximum - flush with it, minimum - with a deviation of no more than 10 degrees from the horizon, if you draw an imaginary straight line through the highest points of the chimney and skate. The last criterion is valid for the highest point of the pipe if it is located at a distance of more than 3 m from the ridge. The height of the chimney above the roof must be at least 50 cm. You should not remove the chimney at the level of the roof windows in order to avoid the entrainment of carbon monoxide gases into the room.

The standards regarding the location of the chimney relative to the roof ridge are set out in SNiP41-01-2003 and SP 7.13130.2009.

Determining the location of the chimney relative to the ridge and its height is a necessary stage in drafting a heating system. But in addition to this aspect, it is necessary to take into account a lot of other conditions and initial data: the type of fuel, the power of the boiler, the properties of materials, the presence of additional channels that remove the combustion products from the fireplace, stove, climatic indicators, the predominant direction of the wind. After reviewing the requirements of SNiP for the height of the chimney, additional calculations need to be made. For example, calculate the cross section of the chimney. Calculations for complex projects with a large number of objects must be performed by professionals. Operating a faulty designed chimney can be life-threatening.