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Chimney Draft Calculator| Improve Your Chimney’s Efficiency

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A chimney draft is a force that helps to draw combustion gases and smoke out of a chimney. It is crucial for the proper functioning and safety of a fireplace or stove. The chimney draft depends on several factors, such as the height of the chimney, the density of the air, and the difference in temperature inside and outside the chimney.

Importance of calculating Chimney Draft

Calculating the chimney draft is essential for designing an efficient chimney system and maintaining its performance. It helps ensure that combustion gases and smoke are properly vented, reducing the risk of fire hazards and promoting a healthier indoor environment.

Chimney Draft Calculator

introduction to the calculator

A Chimney Draft Calculator is a tool used to determine the chimney draft, enabling users to optimize their chimney system’s performance and safety. It uses the Chimney Draft Formula to calculate the draft based on various factors.

Chimney Draft Formula explanation

The Chimney Draft Formula is as follows:

D = h * p * (1 – To / Ti) * g

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  • D is the chimney draft (pascals)
  • h is the height of the chimney (m)
  • p is the density of the air (1.292 kg/m^3)
  • To is the temperature outside (C)
  • Ti is the temperature inside the chimney (C)
  • g is the acceleration due to gravity (9.81m/s^2)

Factors affecting Chimney Draft calculation

  1. Height of the chimney
  2. Density of the air
  3. Temperature inside the chimney
  4. Temperature outside the chimney

Step-by-step example of Chimney Draft calculation

Random values used for the example

In this example, we will calculate the chimney draft using the following random values:

  • Height of the chimney (h) = 15m
  • Density of the air (p) = 1.292 kg/m^3
  • Temperature inside the chimney (Ti) = 40C
  • Temperature outside the chimney (To) = 30C

Explanation of each step in the calculation

  1. Calculate the temperature difference ratio: (1 – To / Ti) = (1 – 30 / 40) = 0.25
  2. Multiply the height, air density, temperature difference ratio, and gravity: D = 15 * 1.292 * 0.25 * 9.81 = 47.529 pascals

Applications of Chimney Draft Calculator

Optimizing Chimney performance

The Chimney Draft Calculator helps users design and optimize their chimney system to ensure proper venting of combustion gases and smoke.

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Designing and maintaining chimneys

The calculator enables users to make informed decisions about chimney design, maintenance, and repair to enhance the safety and efficiency of their chimney system.

Frequently Asked Questions (FAQs)

What is the purpose of a chimney draft calculator?

The purpose of a chimney draft calculator is to help homeowners, builders, and chimney professionals determine the draft of a chimney system. This information is essential for optimizing the performance and safety of the chimney, ensuring proper venting of combustion gases and smoke, and reducing fire hazards.

How do I measure the height of my chimney?

To measure the height of your chimney, measure the distance from the base of the chimney (usually at the level of the fireplace or stove) to the top of the chimney. Ensure that you are measuring in a straight line and not along the slope of the chimney if it is slanted.

How do I determine the temperature inside my chimney?

The temperature inside the chimney can be estimated by taking the temperature of the flue gases or by consulting the appliance manufacturer’s guidelines. Alternatively, you can use a digital thermometer or a thermocouple to measure the temperature directly.

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Does the chimney draft change with different weather conditions?

Yes, the chimney draft can change with different weather conditions. Factors such as air density and outdoor temperature can affect the draft. For instance, colder outside temperatures can result in a stronger draft, while warmer temperatures may cause a weaker draft.

Can I use the chimney draft calculator for all types of chimneys?

The chimney draft calculator is suitable for most types of chimneys, including masonry, metal, and prefabricated chimneys. However, specific applications or unique chimney designs may require additional considerations or modifications to the formula. In such cases, consult a professional chimney expert for guidance.


The Chimney Draft Calculator is an essential tool for homeowners, builders, and chimney professionals to optimize the performance and safety of a chimney system. By understanding the factors affecting chimney draft and using the calculator to make informed decisions, users can ensure proper venting of combustion gases and smoke, reduce fire hazards, and maintain a healthier indoor environment.

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