Chimney top
The chimney head (also Essenkopf , Austrian chimney head ) is the part of the (house) chimney that visibly protrudes beyond the roof skin . The chimney flue gases are discharged into the open via it . As a visible building component, it influences the building's perception.
A chimney head consists of at least one shaft and one mouth. Additional components can be a cover plate, a head cover or an attachment.
technical requirements
The free flow of the exhaust gases should not be hindered, the mouth construction should therefore not have any significant constrictions, any protection against penetrating precipitation must have a minimum distance to the mouth.
In order to minimize the effects of wind on the area of the mouth, which hinder drafts, the mouth should be designed higher than the surrounding roof components. The escaping exhaust gases must not pose a risk to residents or neighbors, so the mouth must be higher than the surrounding windows, dormers or balconies. The chimney head must be manufactured in such a way that wind loads do not endanger the statics. It must not have any loose parts.
If no upper cleaning option is installed under the roof for the chimney sweep, the mouth area must be easily accessible for the chimney sweep and without danger. If the chimney head protrudes very high above the roof cladding, another cleaning opening may have to be installed above the roof.
Structure and components
shaft
The shaft is traditionally made from brickwork or quarry stone . Modern, brick-built chimneys usually consist of mantle bricks, possibly an insulating layer on the inside and possibly an inner pipe leading to exhaust gas. Lightweight concrete , concrete , brick chippings , vermiculite , calcium silicate panels and, more rarely, sand-lime brick , aerated concrete or clay are widely used as materials for mantle stones . The mantle stones should be protected from the weather by cladding over the roof.
The following types of cladding are common on modern chimneys:
- Cladding with a prefabricated head z. B. from fiber cement panels
- Advantage: Quick to assemble, with some manufacturers with rear ventilation as protection against moisture
- Prefabricated heads are available in many structures and colors and can therefore be ideally adapted to the roof.
- Not the cheapest option
- Slating with slate plates or sheet metal with galvanized steel sheets or aluminum sheets
- Often taken over by the roofer.
- Walling with clinker bricks
- Advantage: By using the same clinker brick as the house, good color and style integration.
- Disadvantage: This cladding often gets damp over time, as no air exchange can take place.
- Difficult to manufacture, scaffolding, etc. necessary.
- Quick to manufacture, inexpensive, short service life. The color can be adapted to the roof.
Cover plate
Cover plates protect the mouth area from the weather. In addition, they can improve the static properties of the chimney head (introduction of weight) and serve as a static guide for attachments or covers. In modern, rear-ventilated chimneys, the cover plate can also take on the function of introducing combustion air or extracting exhaust air. Conventionally, cover plates are handcrafted on site from concrete or prefabricated concrete cover plates are used. Modern variants can also be made from fiber cement panels or from stainless steel sheets. These panels can be designed with a drip edge so that rainwater drips past the cladding.
muzzle
The chimney mouth is the area of the head where the exhaust gases are led outside. In modern chimneys with an inner pipe carrying exhaust gas that ends below the cover plate, the mouth area can be formed with an expansion joint plate, which is inserted between the (concrete) cover plate and the inner pipe and compensates for the linear expansion of the temperature-loaded inner pipe. Other modern variants lead the inner pipe carrying exhaust gas through the cover plate and protect the resulting annular gap between the pipe and cover plate with a cover apron or a rain collar from penetrating rainwater. Cover aprons or rain collars are attached to the inner pipe leading to the exhaust gas.
Chimney cover
Chimney covers are used to keep rainwater from entering the mouth, in a flat form known as a Meidinger disk (after Heinrich Meidinger ), and in a corrugated form as a Napoleon hat. The covers can be anchored on the cover plate or are inserted into the exhaust port. The distance between the cover plate and the mouth should be at least half the clear inside dimension or inside diameter of the chimney so as not to obstruct the free flow. Special case of rain covers on chimneys to which heat generators with low exhaust gas temperatures are connected: The water vapor contained in the exhaust gases can condense on the cover in very cold weather. This can result in icing that hinders the free flow of the exhaust gases.
Chimney tops
Chimney tops are used to improve the chimney function, to protect the building fabric or to enhance the appearance of the chimney head. A distinction is made between rigid and constructions with moving parts. On the material side, a distinction is made between steel attachments, concrete attachments and ceramic attachments.
Steel attachments are made from galvanized sheet steel or stainless steels. The advantage is the simple production and assembly, the disadvantage of galvanized constructions is the short service life (rust) and the appearance.
Concrete attachments are mortared on the cover plate, are usually very short and often have lamellar openings on the side. The advantage is the low price, the disadvantage is the short service life, because sulfur-containing exhaust gases can attack the concrete.
Ceramic chimney tops have an extremely long service life because they are acid-resistant and are visually appealing. The higher installation effort is a disadvantage.
Technical function of the rigid attachments: By extending the effective chimney height, a draft improvement is achieved. By moving the mouth outlet upwards in the direction of the ridge, wind influences that disrupt the exhaust gas outlet can be avoided. The exhaust gas discharge can be accelerated by slightly narrowing the cross section and thus a better solution of the exhaust plume can be achieved even in windy conditions. Due to the lamellar design of the attachments, wind flowing in horizontally can also accelerate the exhaust gas discharge. Since the exhaust gas is discharged significantly above the cover plate, thermal disadvantages due to the heating of the cover plate on summer days, disruptive wind turbulence in the area of the chimney head shaft and the recoil of chemically aggressive exhaust gas on the (concrete) cover plate or the shaft can be reduced.
Technical function of the movable attachments: These are often equipped with rotatable lamellar balls or rollers at the mouth. When there is wind, these generate an additional negative pressure, which is intended to increase the exhaust gas velocity in the chimney. In the absence of wind, however, these rotatable attachments can represent a drag that impairs flow. Another embodiment has a windshield in the mouth area, which automatically aligns itself against the wind direction. This should prevent disruptive wind influences.
- Chimney heads, working examples
Chimney head detail in Venice, Italy
Chimney top with cover and wind chime in Lemmer, Holland
Chimney head with brick cover in Bruges, Belgium
Chimney heads in Istanbul, Turkey
Head detail, Dun-sur-Meuse, France
Ceramic head extensions in Chester, England
