Orthogonal Static Chimney Cowl - Large Format for Rectangular Flues
Orthogonal static cowl: the cap for large rectangular flues
When a flue exceeds the size of a standard cowl, installers end up improvising: on-site build-ups, cut pieces, and caps that neither seal nor draw properly. This orthogonal static cowl is made exactly for that case: it covers a 62 × 31 cm flue on a 79.5 × 48.5 cm base, practically double the surface of a standard model, using solid, unreinforced concrete pieces.
✅ Key advantages
Venturi effect, no electricity or moving parts: wind enters through the side openings and, as the passage narrows, accelerates and drops in pressure. That suction created right above the flue mouth draws the smoke upward. The harder the wind blows, the better it draws: no motor to fail, no electricity bill.
Very wide flue section: 62 × 31 cm of usable flue, designed for high-output fireplaces, wood-fired kitchens, ovens and shared outlets where a small cap would choke the exhaust.
High-density vibro-compacted concrete, wet-cast: the mix is poured fluid into the mold and compacted by vibration, giving a dense piece with a smooth finish and very low porosity. Being so compact, it holds up with no need for internal steel reinforcement.
No reinforcement, no rust, no maintenance: there's no steel inside for the acidic smoke condensates or rainwater to corrode. Nothing to paint, tighten or replace over the years.
Modular assembly: the set is made up of a base piece, four intermediate pieces and a cap piece, so it can be carried and taken up to the roof in parts instead of as a single 168 kg block.
Two finishes: White and Cement Grey, to blend with light façades or neutral-toned roofs.
🏗️ Recommended applications
Wood-burning fireplaces and large hearths in single-family homes, farmhouses or country houses.
Wood-fired ovens, grills and roasters in hospitality and catering.
Shared ventilation or extraction ducts in multi-family buildings.
Renovation of old brick-built chimneys with a large rectangular flue.
Agricultural or industrial buildings with high-output smoke outlets.
📋 Technical specifications
Assembled set dimensions: 84 × 51 × 57 cm.
Support base: 79.5 × 48.5 cm.
Free flue section: 62 × 31 cm.
Set weight: 168.10 kg (183.10 kg with packaging).
Material: high-density vibro-compacted concrete, no internal reinforcement.
Set composition: 1 base piece + 4 intermediate pieces + 1 cap piece.
Colors available: White and Cement Grey.
Use: outdoor, on the roof.
Packaging: single unit (complete set).
🧰 Installation
Check that the top of the flue is plumb, flat and clean, and that the internal flue section doesn't exceed 62 × 31 cm.
Level the top of the chimney with mortar until you have a continuous horizontal surface for the whole base to rest on.
Bed the base piece on fresh cement mortar and check the level in both directions before it sets.
Stack the four intermediate pieces one on top of another, aligning the faces and keeping the side air openings clear.
Finish with the cap piece and seal only the outer joints. Never block the side openings: they're what create the suction.
Let it cure for at least 48 hours before lighting the fireplace, and don't load the piece in the meantime.
📦 Available formats
Complete set, 84 × 51 × 57 cm, in White, single-unit packaging.
Complete set, 84 × 51 × 57 cm, in Cement Grey, single-unit packaging.
💡 Professional tip: measure the flue on the inside, not the outside. This is the most common mistake: the outer size of the brickwork is measured, a cowl is ordered that then sits unsupported over the opening, and the top has to be built up with the material already up on the roof. A second check that saves headaches: the mouth should sit at least 1 m above the highest point within a 2 m radius — ridge, parapet, tree or neighboring building. That's standard good practice in Spain; if the chimney sits lower, not even the best cowl will stop downdrafts sending smoke back inside.
