What is a deflector: how to make and install on the chimney

Has it ever occurred to you that your fireplace may not always operate as well as it should? Perhaps you’ve had problems keeping the temperature constant or smoke blowing back into your house. Installing a chimney deflector could be one way to solve these issues. However, what is a chimney deflector and how can it enhance your fireplace’s functionality?

Installed at the top of your chimney, a chimney deflector—also called a chimney cap or a chimney hood—improves the functionality of your chimney. It prevents downdrafts, which is the main of its many beneficial functions. When wind blows down your chimney, it creates a downdraft, which prevents smoke and fumes from being safely vented outside and into your home. A deflector lessens this issue by diverting wind and rerouting it away from the chimney opening.

A chimney deflector also serves as a shield to keep animals, debris, and rain out of your chimney. Debris like leaves and twigs can build up in your chimney, preventing airflow and creating a fire hazard. Squirrels and other birds may attempt to build their nests in your chimney, which could result in obstructions and further damage. These undesirable intruders can be successfully kept out of your chimney with a deflector installed correctly, keeping it clear and operational.

You may be wondering how to make and install a chimney deflector now that you know how important they are. Although prefabricated deflectors are sold, you can also use basic materials and tools to make your own custom deflector. We’ll go over several do-it-yourself chimney deflector construction techniques and provide detailed installation instructions in the following sections.

Purpose of the deflector

The state of the atmosphere directly affects how natural exhaust ventilation functions. The temperature and pressure differential between the building’s interior and exterior causes the draft in the pipe.

It is the wind that modifies the engineering system. Depending on the strength and direction of the flows, gusts can either increase or decrease the draught.

By adding a deflector to the chimney, you can lessen the impact of outside air quality on ventilation. The header speeds up the ducting of dirty air out of the building and reroutes wind currents in the proper direction.

The ventilation nozzle also carries out the following duties:

Natural ventilation can operate 20% more efficiently when a deflector is used.

Device, principle of operation of headings

The size, design, and shape of ventilation headers vary. Both basic mushroom-shaped caps and intricate spherical, H-shaped nozzles are manufactured. All models, regardless of design, have three fundamental structural components:

A diffuser consisting of a truncated cone sits at the base of the casing. The device raises pressure while slowing down air flow. The diffuser’s lower section is used as a fastening point to secure it to the exhaust pipe.

The protective hood shields the exhaust shaft and diffuser from bird infiltration, precipitation, and debris. Typically, the element is fashioned like an umbrella. The hoods in rotating headboxes are constructed from a weather vane, a net, and a ball. There are no umbrellas on H-shaped diffusers.

The fixture’s body is made up of a cylinder. In fixed models, posts hold the parts in place permanently. There is a bearing-rotating mechanism on movable headers.

Certain deflector models, like DC, have a filter screen installed. The screen understates the draft but captures fine particles up to dust.

Principle of operation

The headliner’s work is predicated on Bernoulli’s law. The pressure and exhaust air from the exhaust duct establish a relationship inside the casing. The velocity of flows is accelerated by the diffuser’s duct narrowing. A rarefaction is produced when the pipe’s pressure drops.

Let’s examine the working principle one by one:

1. Installed on the pipe, the capping catches the airflow.
2. The air mass entering the casing is directed into the diffuser with subsequent branching into streams that help to reduce the pressure at the outlet of the ventilation shaft.
3. In the resulting area of rarefaction, the exhaust air leaves the building through a shaft. Wind gusts carry dirty masses into the atmosphere.

When the header is installed at the correct height and has a properly matched design, the pressure difference increases at the ventilation shaft or chimney outlet. The volume of air exchange rises with the difference.

Pros and cons of using baffles

Flashing is required to complete the roof’s chimney outlet or ventilation system. There is no denying that installing a hood is necessary. I suggest weighing the advantages and disadvantages of the design in order to get a general sense of its usefulness.

• protection of the duct from precipitation, debris, bird penetration;
• draught amplification;
• Reduces the likelihood of back drafts;
• chimney sparks extinguishing.

One of the drawbacks is that ventilation may be disrupted if upward-directed wind currents strike the header. I suggest adding a cap where the design calls for two cones in order to avoid the issue.

Classification of ventilation headings

Deflectors are categorized according to the manufacturing material. Aluminum, stainless steel, and galvanized headers are thought to be the most practical to use. Products made of copper are pricey. Ceramic and plastic structures have a limited lifespan.

The primary categorization resides in the design elements:

1. Static – have no moving parts.
2. Rotary – consist of a stationary base and a rotating element with blades.
3. Static with a fan – consists of a stationary base. For forced removal of dirty air, the design is supplemented with an axial electric fan.
4. Ejector with rotating body – consists of a stationary base and a cap rotating on a bearing. The wind direction rotation is ensured by a weather vane installed on the top.

With an outer casing, heads can be either open or closed.

The shape is chosen—square, rectangular, or round—to fit the exhaust duct. Transition adapters can be used to install round headers on pipes with a rectangular cross section.

Size range

For ducts with diameters between 100 and 1250 mm, heads are made. The baffle cylinder has a diameter that ranges from 200 to 2500 mm.

Height of cylinder: 120 to 1500 mm. Concurrently, the deflector’s height fluctuates between 170 and 2125 mm. A maximum deviation of ±4 mm is permitted for the standard dimension.

Overview of effective models of ventilation hoods

The design of ventilation baffles for roof ventilation distinguishes them and influences the engineering system’s efficiency.

Air masses can naturally pass through even the most basic models that don’t have any electrical components.

Hoods with fans and automatic controls boost the airflow and automatically adjust the volume and speed of exhaust air that exits through the exhaust duct.

The simplest hood

It is usual to see a fungus-shaped hood on the chimney stacks and ventilation systems of private homes. In theory, the design serves as a deflector. In actuality, the umbrella keeps precipitation out of the pipe. The amount of draught is not significantly affected by the hood.

The fungus’s widespread appeal can be attributed to its straightforward design. It is made by shaping a tin circle into a convex figure, attaching three legs to it with rivets, and then using a clamping clamp to secure it to the pipe.

Wolpert-Grigorovich hood

The model’s simplicity of use and effectiveness at work account for its demand. Making the hood out of galvanized sheet metal on your own is not too difficult. There are five parts to it:

• tapered cone diffuser;
• 3 posts;
• cone-shaped umbrella;
• reverse cone-shaped hood;
• ring for fixing to a round chimney stack.

An adapter is needed if the cap is to be installed on a rectangular chimney.

A downward-expanding cone is the design. Beneath the hood is a fixed plate with a reverse cone shape. allows more air to enter without building up beneath the fungus cap.

The flow velocity under the lower cone-shaped plate increases as a result of the channel narrowing. By increasing the pressure difference, the thrust is enhanced.

CAGI nozzle

Because of the wind head and the ensuing pressure differential, the design aims to increase the draft. There is a traditional cone-shaped hood with three legs inside the nozzle. There is a cylindrical screen outside the umbrella that is fastened to the posts.

Among the nozzle’s features is the ability to attach it to the air duct using a flange, bandage, rail, or nipple.

I view the wintertime ice formation on the cylindrical screen’s inner walls as a significant drawback.

The outlet opening becomes blocked as the thickness of the ice increases.

The nozzle is susceptible to currents in the wind. Inside the housing, a draft resistance is produced during the doldrums. The deflector is useful for home ventilation because it can be manufactured independently and is long-lasting.

With the exception of sporadic icing, the CAGI nozzle performs admirably.

Stato-mechanical ventilation nozzle Astato

The French company that developed the deflector is honored in the device’s name. The manufacturer has included a fan for use when operating in active mode.

After the motor starts, the vent channel’s aerodynamic value is preserved. The total value of the air pressure and fan head is equal to the rarefaction that is produced.

When the motor is turned off, the deflector can still function in passive mode. The total of wind pressure and gravity equals the rarefaction that is produced.

Both single-story and multi-story buildings have the deflector installed. There is a nipple fastener available for round ducts. The nozzle is connected to rectangular ducts using an adapter.

One drawback of the two-speed fan model is its high price, ranging from 1300 to 4000 u.е.

DC ventilation deflector

The DS nozzle looks like an imitation of Astato from the outside. Its lack of an electric fan and other moving parts sets it apart from the French baffle.

Within the casing, three conical plates are installed. Above the exhaust ducting is one of the hood’s truncated channels.

The additional vacuum that the pressure difference between the inside and outside of the baffle body creates increases the draught.

The hood was originally intended to be mounted on the exhaust hood to allow for the building’s natural air discharge. can be paired with a fan, but the fan is an additional purchase.

The deflector allows 5–10 m/s of wind flow, which raises the draught to 10–40 Pa. At +25 o C, 50% humidity in street air, and a 30 o deviation from horizontal wind flow, maximum performance is recorded.

Turbo deflector

A stationary base and a rotating ball-shaped head make up the rotary nozzle.

The turbine element has thin metal blades that resemble a drum. A slight wind moving at 0.5 m/s in the flow’s direction initiates the rotation.

Part of a vacuum is produced underneath the hood. The duct’s end creates a rarefaction, which lessens the possibility of back drafts.

The turbo deflector can extract air from the hood up to four times more efficiently than hoods with fixed components.

Hot streams leave the room more quickly during the day, which reduces the need for air conditioning. Ice and condensate hardly ever accumulate inside the revolving spherical hood.

Economical functioning because there is no electric fan. The turbo deflector extracts heavy gases, steam, and dust from the ventilation duct in addition to dirty air.

I view the rotary nozzle’s inability to function during doldrums as a significant drawback.

Rotating vane

A series of bent canopies mounted on a bearing unit for rotation make up the nozzle. Other names for the design originated from the hood’s shape, which is similar to the hood of a garment or a fishing net.

A weather vane is attached to the top of the canopies. The hood is rotated in the direction of the wind by a guide element.

The weather vane’s unique design has an impact on the working principle.

• The wind flow rotates the weathervane together with the cap along the line of wind movement;
• air flows penetrate under the hood between the gaps of neighboring canopies;
• flows are redirected upwards under the hood;
• According to the laws of aerodynamics, a rarefaction is created due to the pressure drop and increased velocity of moving streams;
• It increases the draft in the exhaust pipe and additionally creates conditions for forced removal of dirty air from the building.

The vane’s design is intricate. The model is not one that I advise using for self-manufacturing. I want to draw attention to the operational limitations. In exhaust ventilation, the weather vane works well with wind loads up to 0.8 kPa.

H-shaped canopy module

Installing the nozzle on a residential building’s roof is not customary. The module is mounted on industrial buildings’ chimneys and exhaust shafts.

When a deflector is installed on the ventilation pipe, the flow into the vertical elements and the subsequent sucking out of dirty air through tubes that are positioned horizontally can increase the draught.

The module’s upper portion is not protected by a canopy. Horizontal tubes provide precipitation protection. Strong gusts of wind are conducive to the H-shaped deflector’s optimal performance.

Unclean air is extracted from the building using wind currents that are directed from the bottom to the top.

Which model to choose

I suggest self-manufacturing Volpert-Grigorovich and TsAGI hoods on a private home’s hood from successful models. Choose a turbo deflector or rotary vane if you decide to purchase.

Folk craftsmen have learned to make H-shaped deflectors from shaped PVC sewer system components, despite their industrial use. Place the nozzle on an outbuilding or rural home’s hood.

To prevent it from melting in extreme heat, an H-shaped deflector is assembled on the chimney using three tees made of stainless or galvanized steel.

In the realm of home heating and insulation, understanding the role of a chimney deflector is crucial. A chimney deflector, essentially a cap placed on top of the chimney, serves multiple purposes. Firstly, it prevents rain, snow, debris, and animals from entering the chimney, thus safeguarding the interior of your home. Secondly, it helps improve the efficiency of your chimney by promoting better airflow, which in turn enhances the performance of your heating system. Making and installing a deflector is relatively simple and can be done with basic tools and materials. By adding this small but effective accessory to your chimney, you not only protect your home but also optimize its heating system, ensuring warmth and comfort throughout the colder months.

Making a deflector CAGI with our own hands

It is simpler to make the Grigorovich hood, which has a mushroom cap-like shape. I suggest going with the CAGI deflector instead of the simple route. The design can improve the draft and avoid the opposite effect, but it is not more difficult to make.

You will need metal scissors, a hand riveter with rivets, a marking tool, and a galvanized sheet of rolled metal for this task. Following material preparation, we start the CAGI’s manufacturing process:

1. Mark out the parts on a galvanized sheet of paper. Cut out a rectangular strip of 15×90 cm with metal scissors. The blank is needed to make a cylindrical body.

1. To make the umbrella, cut a circle with a radius of 11.5 cm from galvanized steel. To give the workpiece a cone-shaped fungus, make a cut from the center to the edge. Bend the circle with your hands so that the notched edges overlap each other. You should get an umbrella that resembles a small cone.

1. Clamp the obtained cone at the junction of the notched edges into the braids. Check the correctness of the shape of the workpiece, tightness of the joints without deformation of the metal.

1. Drill holes along the length of the joint of the cone so that the overlapping edges of the overlapping metal are captured. Use a hand riveter and rivets to join the umbrella seam together.

1. Install 3 rivets at equal distances along the length of the outer seam to secure the joint. With the fourth rivet, fix the edge of the metal located at the back of the umbrella.

1. Cut a second circle of similar size from galvanized steel. Make another cone out of it, but fix the joint at the edge of the umbrella with 3 rivets.The workpiece will be used to make an adapter between the ventilation pipe and the hood.

• From the center of the cone, draw the lobe markings.
• Cut the tip of the hood with a metal hacksaw.
• Cut the lobes with metal scissors, bend at an angle of 90° to the convex side of the cone.

A ring-shaped component with an aperture the same size as the exhaust pipe’s diameter should be delivered.

1. Place the resulting ring temporarily on the exhaust pipe with the lobes facing downwards. Try on the pieces to make sure they fit properly.

1. Make 3 posts to connect the lower ring with the upper umbrella. Cut 3 strips of galvanized steel 20 cm long and 2-3 cm wide.

1. Place the prepared strips evenly spaced on the lower ring of the deflector. Fix each part with 3 rivets.

1. Bend the posts in a "U" shape so that the side projections beyond the borders of the umbrella and the bottom ring are formed. The contour should correspond to the inner diameter of the cylinder, which acts as the deflector body.

1. The racks in the already bent position should have vertical sections with a height of 7 cm. Check the dimensions with a ruler.

1. Place the umbrella on the posts. Mark the attachment points. Drill 2 through holes for each post. Join the parts with rivets.

1. From a cut rectangular 15×90 cm galvanized sheet, bend a ring, but do not join the edges yet. Try on the part by applying it to the vertical elements of the racks. Mark the holes for fixing with rivets.

1. Drill through holes according to the markings. Use rivets to fasten the hood to the uprights. Join the overlapping edges of the ring itself.

On the exhaust pipe, install the completed deflector. Use a clamp to secure the lobes to the duct walls. The CAGI deflector is prepared to work.

Topic	What is a deflector: how to make and install on the chimney
Definition	A chimney deflector is a device installed at the top of a chimney to improve its performance by controlling airflow and preventing downdrafts.
Function	It redirects air currents to create a draft that helps carry smoke and gases up and out of the chimney.
Materials	You can make a deflector from metal, such as stainless steel or aluminum, or purchase a pre-made one.
Installation	To install, attach the deflector securely to the chimney using brackets or straps. Make sure it is positioned properly to effectively divert airflow.
Maintenance	Regularly inspect the deflector for any damage or debris buildup that could hinder its function. Clean as needed to ensure optimal performance.

A chimney deflector can greatly increase the safety and efficiency of your wood stove or fireplace. A deflector helps keep smoke and dangerous gases out of your house by diverting smoke and preventing downdrafts. Moreover, it can lessen creosote accumulation, which is a significant contributor to chimney fires.

Making your own chimney deflector is a reasonably easy do-it-yourself project that can help you save money and give your house a unique solution. Create a deflector that fits snugly over the top of your chimney using simple materials like sheet metal or aluminum flashing and a few simple tools. To keep your deflector from becoming dangerous, make sure it is firmly fastened and take the appropriate safety measures.

For optimal effects, it is crucial to properly position a chimney deflector when installing it. By positioning the deflector at the right height and angle, you can make sure that it successfully redirects airflow, avoiding downdrafts and keeping smoke away from your house. Furthermore, it is essential to perform routine maintenance and inspections on your deflector to guarantee that it stays in good shape and keeps working correctly over time.

To sum up, installing a chimney deflector can enhance the functionality and security of your chimney in an easy and efficient manner. Installing a deflector can help to minimize smoke, lower the risk of chimney fires, and guarantee that your wood stove or fireplace runs effectively, whether you choose to make your own or buy one already built. Throughout the chilly winter months, you can enjoy a warmer, safer home by taking the time to install and maintain a deflector.

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