Understanding the solar chimney and its value for natural ventilation
The thermal draught principle: sun, duct and chimney effect
A solar chimney is a dark or glazed duct heated by the sun. The air inside warms up, becomes lighter and rises. This thermal draught creates a low-pressure zone at the bottom of the duct, which draws in fresh air through dedicated air inlets and extracts stale air at the top.
Use cases in renovation: as a boost to mechanical ventilation or as stand-alone natural ventilation
In renovation, it mainly serves as a boost to improve air renewal during the shoulder seasons or reduce the running time of mechanical ventilation. As stand-alone natural ventilation, it can suit well-cross-ventilated living rooms, but it remains dependent on sunshine. In wet rooms, keep controlled extraction.
The main variants: roof-mounted, façade-mounted, single or double wall
You'll find it roof-mounted (more stable draught) or façade-mounted (simpler to integrate). Single-wall models are compact. A double-glazed wall with an absorber improves the temperature rise and limits losses, especially if the duct is well insulated and fitted with non-return valves.
Designing and sizing your solar chimney in 2026
The parameters that determine airflow: height, cross-section, orientation and pressure losses
A solar chimney works as a thermal draught. The greater the height and the more the air warms up in the duct, the higher the airflow rate. The cross-section then affects velocity. Too small, and you create losses. Too large, and the flow slows down. Orient the collector to the south and limit bends, overly tight grilles and unnecessary lengths, since each obstacle eats into the pressure.
Choice of materials and finishes: absorber, glazing, insulation and durability
For the absorber, a dark matte metal sheet is simple and effective. On glazing, glass resists UV and scratches better, while polycarbonate is lighter. Insulate the back of the collector box to keep the heat in the airflow. Aim for durable materials, protected against corrosion and condensation, with a cleaning hatch.
A pragmatic sizing method: flow-rate targets and quick checks
In 2026, start from a concrete target per room. For example 30 to 60 m³/h for a wet room. Choose a cross-section that keeps velocity around 0.5 to 1.5 m/s. Do a quick check of the draught. Compare the available pressure to the total losses (inlets, ducts, outlets). Adjust height, cross-section or glazed area, then validate under real conditions.
Integrating the solar chimney into the envelope without creating defects
Airflow path through the dwelling: air inlets, penetrations and connections to rooms
A solar chimney only "draws" well if the air has a clear path. Plan for air inlets at the bottom of living rooms, then transfer passages (undercut doors or grilles) toward the areas connected to the duct. Limit lengths and bends, avoid taking air from the attic, and keep controlled flow rates to avoid creating discomfort.
Airtightness and thermal bridges: sensitive points and installation solutions
Every wall penetration is a sensitive point. Treat the duct-to-wall junction with airtight sleeves, suitable adhesive tapes and renders, then ensure insulation continuity around the duct. An insulated sleeve, fixing clamps with a thermal break, and an insulated box on the inside limit cold surfaces and parasitic air leaks.
Managing humidity and condensate: vapour barrier, drainage and protections
Protect the envelope like a rain jacket. On the warm side, connect the vapour barrier or vapour-check membrane properly at the penetrations. On the duct side, plan a drainage path for condensate (slope, collection point), corrosion-resistant materials, and top protections (grille, cowl) that don't block the draught.
Carrying out the installation on site and securing commissioning
Installation steps: solar collector, duct, outlets and valves
For a solar chimney, installation begins with a stable support and roof or façade sealing. Fix the solar collector without a thermal bridge, then connect a rigid, non-combustible air duct. Aim for lasting airtightness on every joint. Plan a protected low air inlet, a rain-protected high outlet, and non-return valves to prevent flow reversal on windy days.
Simple, reliable control: dampers, summer/winter bypass and overheating protection
Keep the control easy to read. Manual or motorised dampers are enough if the position is visible and lockable. Add a summer/winter bypass to limit heat gains in hot periods, and an overheating safeguard that opens a relief outlet or switches to bypass when temperatures run high. Objective: safe operation, even in degraded mode.
Commissioning checks: draught tests, flow-rate measurement and adjustments
At commissioning, check the draught with a smoke test or an anemometer, then measure the flow rates at the grilles. Correct pressure losses, adjust dampers and valves, and record the values on the commissioning sheet. Fine-tuning avoids noise, odours and condensate.
Improving performance and showcasing the solution to your clients
Summer comfort and air quality: concrete indicators to track in 2026
In 2026, your clients want a feel for it, but also proof. Track 3 simple measurements before and after the works. Indoor temperature during hot periods, with the number of hours above a comfort threshold. Humidity, to spot mould risks. And CO2, a good thermometer for air renewal. With these readings, you turn an opinion into a measurable result, without vague promises.
Practical comparison: solar chimney vs mechanical ventilation (cost, maintenance, constraints) by job type
- Solar chimney. Often mid-range cost. Few moving parts. Effective if a draught is possible and the building allows it.
- Single-flow mechanical ventilation. Controlled cost. Regular maintenance of grilles and air inlets. Often the simplest option in renovation.
- Dual-flow mechanical ventilation. Higher cost. Ductwork needed. Relevant when airtightness and insulation are already at the right level.
Consistency with 2026 approaches: energy audit, DPE and renovation argumentation
Tie the solution to a coherent renovation pathway. The energy audit and the DPE address summer comfort, humidity and ventilation. Position the solar chimney as a complementary lever, to be validated according to the dwelling, and put the prerequisites in writing. You secure the decision, and you strengthen your credibility on site.
Key figures
3 to 6 m
Chimney height
2 to 5 m²
Collector area
100 to 300 m³/h
Flow rate achieved
Frequently asked questions
In renovation, the key requirement remains ensuring permanent air renewal: follow the principles of general and permanent ventilation (air inlets in main rooms, extraction in service rooms). Rely on the envelope's best-practice rules/DTU (airtightness, roof/façade penetrations) and document that hygienic flow rates are maintained, especially if mechanical ventilation is reduced. Plan for non-return valves and a "secured" mode (mechanical ventilation or extractor) for wet rooms.
Pierre-Louis Guhur
CEO of Argile
