Short answer: size solar ventilation from how much air you need to move per hour, based on the room's volume and how many times per hour you want to change the air (air changes per hour, ACH). Work out the target airflow in m³/h (or CFM), then choose a fan rated at or above it — and make sure there are enough intake vents for replacement air.
Step 1 — Measure the space
Volume = length × width × average height, in cubic metres (m³).
Step 2 — Pick the air changes per hour (ACH)
Different spaces need different ventilation rates:
| Space | Typical air changes/hour |
|---|---|
| Attic / roof space | Lower (heat exhaust) |
| Workshop / garage | Medium |
| Greenhouse | Higher |
| Barn / livestock | Higher |
Your supplier or local guidance can confirm the right ACH for your use.
Step 3 — Calculate the airflow needed
Airflow (m³/h) = room volume (m³) × air changes per hour.
Then choose a fan whose rated airflow meets or exceeds that number. (To convert: 1 m³/h ≈ 0.59 CFM, or 1 CFM ≈ 1.7 m³/h.)
Step 4 — Provide intake vents
A fan can only exhaust as much as can flow in. Ensure enough intake vent area so replacement air enters freely — otherwise airflow falls short of the fan's rating.
Step 5 — Match the fan type
- Roof/attic ventilators for heat exhaust from roof spaces.
- Wall exhaust fans for greenhouses and rooms.
- Industrial gable fans (up to ~41,000 m³/h) for large sheds and warehouses, often with AC/DC hybrid drive and thermostat.
COTECH Solar offers nine ventilation lines — roof, wall, industrial, ceiling, ducted, tent and skylights — with brushless drive and smart thermostat. See Solar Ventilation or send your space dimensions for a sizing.
FAQ
How do I calculate the airflow I need for ventilation?
Multiply the room's volume (length × width × height in m³) by the air changes per hour you want. The result, in m³/h, is the airflow to target — then choose a fan rated at or above it. Make sure there are enough intake vents so replacement air can flow in.
How do I convert CFM to m³/h for a fan?
Multiply CFM by about 1.7 to get m³/h, or multiply m³/h by about 0.59 to get CFM. Fan ratings may be given in either unit, so convert to compare like with like when choosing a fan for your calculated airflow.
Why do intake vents matter for solar ventilation?
An exhaust fan can only remove as much air as can enter through intake vents. If the intake area is too small, the actual airflow falls well below the fan's rated capacity. Adequate, unobstructed intake vents let the fan reach its rated performance.