Deflector On The Chimney Of The Gas Boiler: Requirements And Installation Instructions

Depending on the type of fuel, a chimney is an indispensable part of the heating system. On its competent arrangement depends how warm it will be in the house.

Gas is a special type of fuel, because it is not safe, so many are concerned about the question: whether a deflector on the chimney of a gas boiler is necessary and whether this will be the right solution to the problem? Let's try to deal with this difficult question in our material.

Article Content:

  • Popular types of draft enhancers
  • What is a deflector?
  • Deflector design
  • Characteristics of popular models
  • How to calculate a static deflector?
  • Self-assembly of the device
  • Assembly of a simple disc model
  • Performities of installation of a rotary deflector
  • Flue deflectors for chimneys
  • Conclusions and useful video on the topic

Popular types of draft enhancers

In modern design there are different kinds of deflectors, so you can choose a model for the house made in any architectural style.

These designs differ in:

  • flat top;
  • two slopes;
  • semicircular top;
  • tiltable top.

Each of them has the following advantages: the flap opening on the baffle allows the control of the combustion products draining.

As a decorative element for an Art Nouveau roof, a flat roof is excellent; the best protection from the weather is a gable mini-roof. As the material for their manufacture is mainly used galvanized metal, but sometimes it is covered with a layer of plastic or enameled.

What is a deflector?

High wind can disrupt the stable operation of the gas boiler. Under such conditions, the automatics often trip and the boiler shuts down. Combustion products from the gas boiler in case of their ineffective removal pose a threat not only to health, but also to life.

In order to increase the draft by optimizing the air flows use  draught stabilizers or deflectors. In translation, its name sounds like a deflector, a deflecting device. It uses the Bernoulli effect based on the pressure drop during the airflow around an obstacle. It deflects the air masses, increasing the force of the main flow of the chimney.

Deflector on the chimney of the gas boiler: requirements and installation instructions

A gas boiler chimney equipped with a deflector will not be damped by strong gusts of wind. The construction becomes more efficient as the draft force increases up to 20%

The draft booster functions efficiently in all wind strengths and even during strong gusts, if present, the draft will not be overturned. But when there is no wind at all, this aerodynamic device acts as an umbrella and is almost inactive, and sometimes reduces the thrust. For this reason, many experts do not recommend installing deflectors on gas chimneys.

Despite the increased requirements for the deflector installed on the chimney of the gas boiler, in some cases it is the only solution to the problem. If this device is not included in the project, it is necessary to coordinate its installation with the gas service. Only having fulfilled this condition, you can proceed to the installation of the deflector.

Deflectors are divided into the following varieties according to the specificity of the device and the associated principle of operation:

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The traditional umbrella-shaped deflector

H-shaped deflector devices

Deflector- Sail effect deflector

Spark deflector model

Deflector design

The deflector prevents the direct air flow into the chimney.

In the standard version it consists of 3 parts:

  1. A top cylinder(diffuser) widened at the bottom. It is fixed to the lower part with special supports.
  2. Bottom tumblerof metal, ceramic or asbestos cement.
  3. Hoodas a cone-shaped umbrella.

The upper part and the bottom cylinder are fitted with circular baffles which deflect the airflow. Some models do not have an upper element. Then the lower cylinder is mounted on the pipe, followed by the diffuser and caps - straight and return.

The device works according to a simple principle:

  • The walls of the cylinder at the top take up the wind impact and direct the air flow to the circumference;
  • due to the sliding of individual air jets on the surface and their rising upwards, the gas coming from the flue is sucked.
  • The flue is enhanced in any wind direction except horizontal. In the latter case there is the formation of air vortices inside the device, cutting off the exit routes of the smoke. This essential drawback is eliminated by adding an additional element - the cone back.

    Deflector on the chimney of the gas boiler: requirements and installation instructions

    Deflector construction consists of a diffuser (2) with a frame (3) mounted on the pipe (1). These elements are located in the shell (4). Above the diffuser there is an umbrella (5) with thermal insulation (6) and a screen (7). The replacement filter (10) is mounted on supports (9) and bolted (11)

    The deflector cone is mounted below the bell. The purpose of the baffle is to allow the air currents to be discharged outside by crushing them.

    Characteristics of popular models

    The baffle models differ both in size and in sensitivity to wind. The most popular models are the TsAGI, Hanzhenkov, Wolpert-Grigorovich, \"Smoke Tooth\", \"Hood\" aka \"Sachok\", and \"Shenard\". The first of these models was developed at the Zhukovsky airdynamic institute.

    The TsAGI is more commonly used in ventilation systems because of the difficulties encountered when cleaning from soot. The second model is essentially the same FAGI, but slightly improved by the inventor. It is essentially an additional cylinder around a pipe with an umbrella cap submerged inside the cylinder for a certain distance.

    Deflector on the chimney of the gas boiler: requirements and installation instructions

    The FACI deflector is the most common choice of homeowners. It has a cylindrical shape. The device is made of galvanized or stainless steel

    The Volpert-Grigorovich deflector has proven itself as a draft enhancer on chimneys. It works effectively in areas with prevailing downwinds. The construction includes 2 cylinders - the lower one with two outlets and the upper one with a lid.

    \"Smoke tooth\" is mounted in a specially provided in the chimney door. Due to the fact that the construction includes two handles, it is possible to regulate the air flow.

    Deflector on the chimney of the gas boiler: requirements and installation instructions

    The lids for the chimneys are made in different shapes. Sometimes they are covered with heat-resistant enamel. Some examples look very decorative

    The \"Hood\" vent has a pivoting design. It consists of a semi-circular groove-shaped air trap mounted on a pivoting rod embedded inside the pipe. The increase of draught through the installation of a wind deflector is due to the turbulence produced by the wind.

    How to calculate a static deflector?

    When making a deflector yourself it is necessary to make calculations and draw a sketch of the future product. The internal diameter of the flue pipe has to be considered.

    Deflector on the chimney of the gas boiler: requirements and installation instructions

    The photo shows the dependence of the size of the deflector on the diameter of the chimney. In order to determine the lower diameter of the diffuser the basic parameter is multiplied by 2, the upper one by 1.5, the height of the diffuser also by 1.5, the height of the cone including the return cone, the height of the umbrella by 0.25, the pipe entrance in the diffuser by 0.15

    For the standard device the parameters can be selected from the table:

    Tube internal diameter (cm)Diffuser height (cm)Diffuser diameter (cm)
    1214.424
    14, 828
    202440
    404880
    5060100

    Таблица allows to choose the size of the deflector without making calculations. But if the corresponding dimensions are not listed there, you still have to arm yourself with a calculator or find the appropriate program on the internet.

    The following formulae are also used for the dimensioning of an individual size:
    - Diffuser size = 1.2 x dwt. tube;
    - H = 1,6 x dwt. tube;
    - Cover width = 1,7 x dwt. tube.

    All dimensions can be calculated for the sweep of the cone. If the diameter and the height are known, the diameter of the circular workpiece is easily calculated by applying the Pythagoras theorem:

    R = √(D/2)² + H²

    Now the parameters of the sector to be subsequently cut from the workpiece are to be determined.

    The full 360⁰ circle L is 2π R. The length of the circle underlying the finished cone Lm will be less than L. From the difference of these lengths determine the length of the arc of the segment (X). For this purpose a proportion is made:

    L/360⁰ = Lm/X

    This calculates the required size: X= 360 x Lm/ L. Thus, if the height of the baffle is 168 mm and the diameter is 280 mm, the radius of the workpiece is 219 mm, and its circumferential length Lm = 218.7 x 2 x 3.14 = 1373 mm. The desired cone will have a circumferential length of 280 x 3.14 = 879 mm. Hence 879/1373 x 360⁰ = 230⁰. The sector to be cut out must have an angle of 360 - 230 = 130⁰.

    When a workpiece is to be cut out as a truncated cone there is a more difficult problem to solve as the known value is the height of the truncated part and not the complete cone. Regardless of this, the calculation is performed on the basis of the same Pythagoras theorem. The total height is obtained from the proportion:

    (D - Dm)/ 2H = D/2Hp

    From where it follows that Hp = D x H / (D-Dm). Knowing this value, calculate the parameters of the workpiece for the full cone and subtract the upper part from it.

    Deflector on the chimney of the gas boiler: requirements and installation instructions

    When knowing the parameters: height of the cone, total or truncated, and radius of the base, one simply determines by simple calculations the outside and inside radius (in case of truncated cone) and then the initial angle and the length of the curve of formation

    Let us suppose a truncated cone, which has H = 240 mm, diameter at base 400 mm and the upper circle must have 300 mm.

    • Total height Hp = 400 x 240/ (400 - 300) = 960 mm.
    • External radius of workpiece Rz = √(400/2)² + 960² = 980.6 mm.
    • Radius of smaller hole Rm = √(960 - 240)² + (300|2)² = 239 mm.
    • Sector angle: 360/2 x 400/980.6 = 73.4⁰.

    Set one arc with radius 980.6 mm and one with radius 239 mm from the same point and draw radii at 73.4⁰. If you plan to overlap the edges, add allowances.

    About the details on how to construct the deflector on the chimney by yourself, please read below.

    Self-assembly of the device

    First the moulds are prepared, then they are laid out on a sheet of metal and the parts are cut out using special scissors. The body is rolled up and the edges are riveted together. Next, the upper and lower cones are fastened to each other, using the edge of the first one, as it is larger and special fastening notches about 1.5 cm wide can be cut in it in several places, and then bent.

    Deflector on the chimney of the gas boiler: requirements and installation instructions

    Assembling a simple baffle is not difficult but if the unit to be assembled is of the rotating type it is necessary to deal with a multitude of parts

    In the lower cone before assembly the 3 props are inserted and uniformly distributed round the circumference using threaded rods. To connect the umbrella to the diffuser, loops of metal strips are riveted on the latter. The studs are screwed into the hinges and secured with nuts for greater reliability.

    Next, the work on the installation of hand-made deflector on the chimney of a gas or other type of boiler is carried out. The assembled device is placed on the pipe and fixed using clamps, allowing no gaps. Sometimes the joint is treated with heat-resistant sealant.

    Assembly of a simple disc model

    The easiest project to implement is to make a disc model deflector. Such a cap for the chimney can easily be made with your own hands. Its geometric parameters depend on the diameter of the pipe:

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    Deflector design for round pipe

    Diameter clamp to attach deflector

    Size of the hood for the chimney

    Distance between the umbrella and the attachment clamp

    In order not to make a mistake in the production and to fit the parts exactly to the required size, it is advisable to make a model of the deflector out of cardboard in advance. At this stage it is easier and simpler to make adjustments to the design. The cardboard blanks at the same time serve as a kind of patterns when cutting the elements of the future deflector:

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    Making a deflector pattern for a chimney

    Assembling a metal chimney umbrella

    Fitting distance posts

    Fixing the deflector fixing clamp

    Fitting features of the rotary deflector

    Turbo deflector, Rotary deflector, rotary turbine, Turbovent - all these names refer to the same kind of mechanical device for enhancing thrust. It consists of a static part connected to the chimney and an active head with blades in the form of a ball.

    The rotary deflector is the only device that is not advised to be mounted on the chimneys of solid fuel and wood-burning fireplaces. Turbovent has the characteristic feature of drawing air from the chimney even when the heating is not working.

    The direction of rotation of this nozzle does not depend on the strength or direction of the wind. It occurs only in one constant direction, creating an incomplete vacuum effect. This results in increased draft power under rarefied air conditions, and the risk of tipping the draft is virtually zero.

    The Turbovent on gas boiler chimneys does an excellent job and can serve as a decoration for any facade. If you compare it to other types of baffles, it is twice as effective.

    The bases of the rotary baffle can be round, square, flat square. Head dimensions range from 100 - 680 mm. Its service life is up to 15 years.

    With all the advantages of the rotary turbine there is one, but significant disadvantage - in no wind the device stops. If at this time there is precipitation at temperatures below 0, the head may freeze and measures will have to be taken to start it up.

    Despite the relative complexity of the design, the rotary deflector is not difficult to install. The device is lightweight, so the effort of one person and time of about 2 hours is sufficient for installation. A suitable place - the highest point of the roof. This location will prevent snow from entering the pipe if precipitation accumulates around it.

    Deflector on the chimney of the gas boiler: requirements and installation instructions

    The rotary turbine head is moved by means of bearings. The device functions autonomously and is very efficient in removing the gases, but it is useless in windless weather

    There is one requirement for the different models of rotary turbines: the temperature of the combustion products above the pipe must not exceed 150-250⁰. The size of the base has to be precisely adjusted to the chimney. Turbine deflector must match the characteristics of the boiler, and this point must be taken into account when selecting the device.

    Turbine deflectors from different brands are present in the market. Among the most reputable are Turbovent, Turbomax, Rotowent. The first manufacturer produces products with a base of different geometry.

    They can be identified by marking TA-315, TA-355, TA-500. The number indicates the diameter in case of round section or dimensions of rectangular base.

    The turbomax deflector Turbomax is produced by a Belarussian company. The devices are made of high quality material - stainless steel from a European supplier. Rotowent is also made of stainless steel, supplied from Poland. It looks harmoniously on any type of roof. Suitable for both chimney and vent pipes. It withstands high operating temperature - approx. 500⁰.

    Chimney weather vane

    The chimney weather vane is designed so that gases coming out freely from the leeward side increase the draft force in the chimney. The device is made of heat-resistant steel well proven in conditions of high temperatures and condensation.

    Beneath the curved canopy of the weather vane is a bearing unit, insuring against the occurrence of problems with rotation. The bearing assembly is bolted to the chimney. A vacuum zone is created when the air flow passes through the space under the canopies.

    Deflector on the chimney of the gas boiler: requirements and installation instructions

    The base of the device is put on the round chimney up to the stop and then fastened with 3 bolts. Tighten the bolts with great care as the pipe may be damaged. The installation is completed by checking the verticality and rotation of the housing

    The disadvantage of chimney vane is that in strong winds they are unstable. The moving part must be periodically cleaned and lubricated. Inside the device often accumulates moisture, and the flue gases leave a trace in the form of deposits.

    The manufacturers themselves advise the use of their devices in the case of the location of the chimney in an unfavorable place. It actually does not strengthen the draft, but only protects the chimney.

    Conclusions and useful video on the subject

    Whether it is necessary to install a draft enhancer at all in the presence of a gas boiler, you will know after watching this video:

    Turbo deflector to make their own hands is not easy, but some skilled people still do it and successfully operate. Watch this in the video:

    Turbo deflector designs are very many, but we must not forget that gas is used for heating. Not all models can be used. Some of them are not suitable in principle because they are designed for ventilation. In order not to block the smoke removal system, it is necessary to consult with a specialist and get permission to install the deflector.

    Are you looking for a deflector for the chimney? Or have experience in making, or installing this device? Please share it with visitors to our site. Also, in the comments block, you can ask questions about the topic of the article.

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