Double Concrete Base for Static Chimney Cowl - Twin-Flue Installation
Double concrete base: two flues solved with a single piece
When a chimney rises with two twin flues (one for the boiler and one for the fireplace, or two homes sharing a stack), the usual approach is to install two separate bases on the same chimney crown. The result is almost always the same: the two pieces end up misaligned, a gap opens between them that has to be filled with mortar, and that joint is exactly where water starts to leak in after two years. This base solves the problem at its root: it is a single 125 × 65 × 5 cm piece that houses both 31 × 31 cm flues, with no central joint to seal and nothing to fall out of alignment.
✅ Main advantages
No central joint: both openings are cast in the same piece, with the exact spacing and square faces. There is nothing to set out on site and no need to adjust two bases by eye on the roof.
Real watertightness: with no joint between the two flues, the weak point where water gets in disappears. The only joint to seal is the outer perimeter, which is far better protected.
Compatible with round and square chimney cowls: you can mount the tower you need on each flue, round or square, depending on the look of the whole and the section of the duct.
Concrete with no internal reinforcement: the acidic condensates from the smoke and the rainwater have no iron to oxidize. The piece does not swell, does not spall from corrosion and requires no maintenance.
Wide load-bearing surface: with a 125 × 65 cm footprint, it spreads the load of the two towers over the entire chimney crown instead of concentrating it on two small supports.
Two finishes: Blanco and Gris Ciment, to match the color of the masonry or the rest of the finishing.
🏗️ Recommended applications
Chimneys with a fireplace flue and a boiler flue in the same stack.
Shunt ducts or flues shared between two homes in multi-family buildings.
Double ventilation and extraction outlets on flat or pitched roofs.
Refurbishment of double chimney crowns that have been leaking for years through the central joint.
New builds where you want to unify the finishing of two twin flues.
📋 Technical data sheet
Piece dimensions: 125 × 65 × 5 cm.
Section of each flue: 31 × 31 cm.
Interior dimensions: 17 × 31 × 29 cm.
Unit weight: 67.3 kg.
Units per pallet: 10 (pallet weight, 689 kg).
Material: concrete, with no internal reinforcement.
Available colors: Blanco and Gris Ciment.
Compatibility: round and square static chimney cowls.
Use: outdoor, on roofs.
Packaging: single unit or pallet of 10 units.
🧰 Installation
Check that both ducts have a section of 31 × 31 cm or smaller and that the distance between their centers matches that of the piece. Always measure inside the flue.
Level the top of the stack with mortar until you have a continuous horizontal plane under the entire 125 × 65 cm footprint.
Lift the piece with mechanical means or with two workers: it weighs 67.3 kg and cannot be handled with one hand.
Set the base on fresh mortar, centering the two openings over the flue mouths, and check the level in both directions before the mortar sets.
Seal only the outer bearing perimeter. Do not block or reduce the section of the openings.
Mount the towers of each chimney cowl on top and let it set for 48 hours before starting up the appliances.
📦 Available formats
125 × 65 × 5 cm in Blanco, as a single unit or in a pallet of 10 units.
125 × 65 × 5 cm in Gris Ciment, as a single unit or in a pallet of 10 units.
💡 Professional tip: before ordering the base, go up on the roof and measure the distance between the centers of the two flues, not just the section of each one. It is the measurement most often forgotten and the one that decides whether the piece fits or has to be returned: if the ducts are farther apart than the base allows, there is no way to adjust it and you will have to go back to two separate pieces. And do not use the installation as an opportunity to «join» the two flues on the inside in the belief that they will draw better: two connected ducts steal draft from each other and end up sending smoke back from one to the other. Each flue, independent all the way to the mouth.
Frequently asked questions
What is the double concrete base for?
It is a single piece that houses two twin chimney flues, so there is no central joint to seal and no two bases to align. Static chimney cowls are mounted on top of it.
What are its dimensions and weight?
The piece measures 125 x 65 x 5 cm, with 31 x 31 cm flues, and weighs 67.3 kg per unit. The interior dimensions are 17 x 31 x 29 cm.
Is it compatible with round and square chimney cowls?
Yes, it is compatible with both round and square static chimney cowls. You can mount the tower you need on each flue.
What colors is it sold in and how many units come on a pallet?
It is sold in Blanco and Gris Ciment, as a single unit or in a pallet of 10 units. The pallet weighs 689 kg.
What should I measure before ordering it?
Check that both ducts have a section of 31 x 31 cm or smaller, and measure the distance between the centers of the two flues to make sure it matches that of the piece. If you have any doubts, write to us and we will help you.
Frequently Asked Questions
¿Por qué una base doble y no dos bases sueltas?
Porque la junta entre dos piezas independientes es el punto por donde entra el agua. Con una sola pieza no existe esa junta central y la estanqueidad la resuelve el perímetro exterior, mucho más protegido.
¿Qué tengo que medir antes de pedirla?
Dos cosas: la sección interior de cada tiro (debe ser de 31 x 31 cm o menor) y la distancia entre los ejes de ambos conductos, que tiene que coincidir con la de la pieza.
¿Sirve para aspiradores redondos o para cuadrados?
Para los dos. La base es el apoyo común; encima se monta en cada tiro la torre que se prefiera, redonda o cuadrada.
¿Puedo unir los dos tiros por dentro?
No. Dos conductos comunicados se roban el tiro entre sí y el humo de uno acaba saliendo por el otro. Cada tiro debe llegar independiente hasta la boca.
¿Cuánto pesa y cómo se sube?
67,3 kg por unidad. Requiere medios mecánicos o dos operarios; no es una pieza de manipulación individual.
¿Se oxida o hay que darle mantenimiento?
No lleva armadura de acero interior, de modo que ni los condensados ácidos ni la lluvia tienen hierro que atacar. No pide mantenimiento.
Todo excelente. Tras una primera equivocación con el producto elegido, el equipo de atención al cliente se puedo a trabajar para solucionar el problema y darme una solución adecuada.
