The Height Of The Chimney Relative To The Ridge Of The Roof, How To Calculate It Correctly And How It Affects Draft

2024 Author: Bailey Albertson | [email protected]. Last modified: 2023-12-17 12:53

How to independently calculate the height of the chimney

There are many options for stoves and boiler rooms for private houses today, but each of them is equipped with a chimney to remove combustion products. The installation of this structure is not so difficult, but an independent calculation of the height of the chimney sometimes causes difficulties.

Content

• 1 Influence of chimney height on draft
• 2 Chimney height on the roof: fire regulations

• 3 Calculation of the chimney height

  • 3.1 Independent calculation of the chimney height

  • 3.2 Calculating the chimney height using a special program

    • 3.2.1 Online calculator on the Pechi.su website
    • 3.2.2 Chimney calculation program on the Defro.pro website
    • 3.2.3 Chimney height calculator on the ProstoBuild.ru website
  • 3.3 Video: calculating the height of the chimney relative to the roof ridge

Effect of chimney height on draft

Draft is the ventilation effect that any stove gives. The air that enters the house through the slots in the lower part of the facade, heats up, passes through the ventilation holes of the stove, enters the chimney and goes outside. In its place comes dense cold air, which provides the thrust force of the furnace. The greater the temperature difference inside and outside the pipe, the stronger the draft.

The higher the chimney, the longer the air stays in it on the way out and the greater the temperature difference is created at the inlet and outlet of the chimney. Therefore, the thrust force in a furnace with a high chimney is greater. Back draft can occur in a low chimney: combustion products in this case go straight into the house. On the other hand, an excessively high chimney can create a vortex of fire in the furnace. Therefore, the calculation of the chimney height is required.

If the height of the chimney is insufficient, a wind pressure zone can be created in its upper part, which will cause reverse draft

Chimney height on the roof: fire regulations

According to the fire safety standards detailed in SNiP, nothing should prevent the removal of fuel combustion products from the chimney, including its insufficient height. This document contains the following requirements:

• the height of the chimney above a flat roof must be at least 50 cm;
• the height of the chimney relative to the ridge is calculated depending on the distance between them;
• if the chimney height is more than 1.2 m above the roof ridge, it must be strengthened with stretch marks;
• it is unacceptable to place the chimney in the immediate vicinity of windows, doors and balconies, as sparks flying out of it can provoke a fire. The minimum distance from the above objects is 2 m;
• the minimum distance between the chimney and the nearby tall buildings, trees and other large objects is 6 m, otherwise a wind back zone will form;
• the ventilation ducts of the house should not be lower than the chimney.

Chimney height calculation

To calculate the height of the chimney, you need to know the basic parameters of the house and the stove. You can make calculations yourself or using a special program.

Self-calculation of the height of the chimney

Consider the SNiP requirements for the height of the chimney relative to the roof ridge:

• when the chimney is located at a distance of up to 1.5 m from the roof ridge, its minimum height above the ridge should be 0.5 m;
• if the chimney is supposed to be located at a distance of 1.5–3 m, its head must be raised to the level of the highest point of the roof;
• at a greater distance from the chimney, the height of its installation is determined by a fictional line drawn from the ridge at an angle of 10 ^o to the horizon.

It is necessary to measure the distance from the pipe to the ridge of the roof horizontally between the vertical axes of the chimney and the ridge

In the latter case, more painstaking calculations will be required.

1. In the drawing of the house from the ridge down, a line is drawn at an inclination of 10 ^o. The intersection of this line with the axis of the future chimney will be the correct location of the pipe head.

   

   To calculate the height of the chimney located at a distance of more than 3 m from the ridge, the roof must be drawn a line at an angle of 10 degrees from the horizon

2. The height of the head is calculated using the following formula: h _chimney = h _house - S / tg80 ^o, where h _chimney and h _house are the height of the chimney and house, respectively, S is the distance from the chimney to the ridge of the roof, and tg80 ^o is the required parameter to calculate the side of interest the resulting triangle. It is approximately 5.67.

For example, with a house height of 8 m and a distance from the chimney to the ridge of the roof 6 m, h _chimney = 8 - 6 / 5.67 = 6.94 m.

A different approach is required to calculate the height of the chimney in the event that there is an obstacle - a building standing next to it, a tall tree, etc. A tall object forms a wind pressure zone: the air flows meet resistance and do not pass by the chimney, but return and thereby cause reverse draft … To determine the wind stagnation zones need to draw a line relative to the ground at an angle of 45 ^to so that it passes through a corner of the house and ended at the top of a nearby high object. The pipe must be positioned above this line to avoid back draft.

The pipe of the house should go beyond the wind support zone so that there is no reverse thrust

Calculation of the chimney height using a special program

On the net you can find various online calculators for calculating the height of the chimney relative to the roof ridge. For the uninitiated in engineering systems, this is one of the simplest and most accurate options. It is enough to enter the required parameters in the appropriate fields and get the desired height value. The programs use the same formula as above.

Let's consider the work of calculator programs with specific examples.

Online calculator on the Pechi.su website

Calculator page address -

1. The calculator is a visual diagram showing the main parameters of the house.

   

   In order to calculate the height of the chimney installation H, you need to enter only two parameters: the height of the house from the base to the ridge of the roof H1 and the distance from the ridge of the roof to the chimney L1

2. We enter the parameters of the house from the previous example into the marked cells.

   

   Enter the data from the considered example into the indicated cells

3. After entering the parameters, press the button "Read!" and we get the minimum chimney height. In our case, this is 6.94 m.

   

   The program gives the same value that we got manually - 6.94 m

The program in question is quite simple and understandable to any user. In addition to the height of the chimney, it allows you to calculate the diameter of the round chimney according to the given power of the heating boiler.

Chimney calculation program on the Defro.pro website

Calculator page address - https://defro.pro/chimney-calculator.html. On this site, calculations are carried out according to a different principle. The program is not so intuitive, but it is also convenient to use if you have already decided on a home heating system.

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The program on the defpro.ru website is quite functional and allows you to take into account the type of fuel, boiler data and some additional requirements for the chimney

It is worth noting that the program immediately provides an example of calculation with the results and calculates not only the height of the chimney, but also its inner diameter. Here you can set several additional characteristics of the flue pipe.

When you add a sudden narrowing and a triple turn of the chimney, its height increases by 1.5 times

Chimney height calculator on the ProstoBuild.ru website

The page address with the calculator is

1. This is a simple and intuitive service that requires you to enter only two parameters: the height of the house and the distance from the ridge to the chimney.

   

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   The program asks to set two dimensions: A - the distance from the roof ridge to the chimney and H1 - the height of the roof ridge from the base of the house

2. The difference with this program is that it can take into account the presence of an obstacle near the house. Let's try this option.

   

   When an additional parameter is included in the calculation - the presence of an obstacle in front of the house - new fields appear: the distance from the chimney to the obstacle L and the height of the obstacle H2

3. We set the data on the presence of a tree with a height of 12 m at a distance of 6 m from the house and we obtain the desired height of our pipe - 12.5 m. As expected, it should be installed above the tree.

   

   The result is displayed at the bottom of the diagram, it is 12.5 m

Programs for calculating a chimney are best used in combination, since the capabilities of each of them are limited, but at the same time they complement each other.

Video: calculating the height of the chimney relative to the roof ridge

Calculating the height of the chimney relative to the ridge of the roof is not the most difficult engineering task, so if you wish, you can do it yourself or using one of the many programs available on the Internet.