Fan Types: Axial vs Centrifugal Fans, Panel Fan and Exhaust Fan Airflow (m³/h) Sizing
Axial vs centrifugal fans, electric fan and exhaust fan types, panel fan airflow from heat loss and m³/h selection for bathroom and kitchen ventilation.
Fan selection rests on two quantities: airflow (m³/h) and pressure (Pa). Axial fans push air along the shaft axis and give high airflow at low pressure; centrifugal (radial) fans turn the air 90° and produce high pressure with less airflow. Electric fans, exhaust fans and panel fans are names these two designs take by place of use.
> Related Category: Browse models by type and size in Fans, Electric Fans and Bathroom and Toilet Exhaust Fans.
1. Axial vs centrifugal fans
| Property | Axial fan | Centrifugal (radial) fan |
|---|---|---|
| Air path | Straight along the shaft | Enters axially, leaves at 90° |
| Airflow | High | Medium |
| Pressure | Low | High |
| Suited to | Free blowing, short ducts, panels, wall and window mounting | Long ducts, filters, bends and grilles |
| Noise | Lower at the same airflow | Quieter at high pressure |
| Examples | Panel fan, electric fan, wall exhaust fan | Duct fan, cooker hood, blower |
Rule: as resistance ahead of the fan grows (long duct, filter, louvre), axial airflow falls quickly; choose a centrifugal fan.
2. Fan types by use
| Fan type | Construction | Use |
|---|---|---|
| Compact axial (panel) fan | Square frame, 80–92–120–150–172 mm; 230 V AC or 12–24 V DC | Cooling electrical panels, devices and cabinets |
| Filter fan | Fan + filter cassette + louvre, IP54 | Panel ventilation in dusty areas |
| Bathroom and toilet exhaust fan | Axial, 100–120–150 mm duct size | Wet room ventilation |
| Wall and window exhaust fan | Axial, 150–300 mm | Kitchens, workshops, stores |
| Duct fan | Centrifugal or mixed flow | Ventilation with long ducts |
| Electric fan | Axial; desk, pedestal, wall and ceiling | Moving room air for comfort |
In compact fans a ball bearing lasts longer at high temperature and in any mounting position; a sleeve bearing is quieter and cheaper but wears faster when hot.
3. Panel fan airflow calculation
The heat lost by devices in a panel must be carried out. Required airflow:
V (m³/h) = 3.1 × P (W) / ΔT (K)
- `P`: total heat loss inside the panel (losses of drives, power supplies, contactors and transformers)
- `ΔT`: difference between the permitted internal temperature and ambient
Example: 400 W of losses, 30 °C ambient, 40 °C maximum inside → ΔT = 10 K
`V = 3.1 × 400 / 10 = 124 m³/h`
- Filters and louvres reduce airflow; read the airflow with filter in the data sheet and add 20–30%. Here a fan of about 160 m³/h with filter is chosen.
- Mount the fan blowing into the lower part of the panel and the exit filter in the upper part of the opposite face; hot air leaves at the top.
- Controlled by a panel thermostat, the fan runs only when needed and the filter lasts longer.
- If ambient is hotter than the permitted internal temperature a fan cannot cool; a panel air conditioner is needed.
- Fan filters clog and reduce airflow; replace them periodically.
4. Bathroom and kitchen exhaust fan selection
V (m³/h) = room volume (m³) × air changes per hour
| Room | Air changes per hour |
|---|---|
| Bathroom, toilet | 6–10 |
| Domestic kitchen | 10–15 |
| Store room | 3–6 |
| Workshop | 6–10 |
Example: a 2 m × 2 m × 2.5 m bathroom = 10 m³; 8 changes → 80 m³/h. A 100 mm fan giving about 90–100 m³/h in free air fits.
| Fan diameter | Typical free airflow |
|---|---|
| 100 mm | 80–100 m³/h |
| 120–125 mm | 150–190 m³/h |
| 150 mm | 250–320 m³/h |
- Every metre of flexible duct and every bend cuts airflow noticeably; above 3 m of duct go one size up or use a centrifugal type.
- Prefer a model with a backdraught shutter, and a run-on timer or humidity sensor in bathrooms.
- Around showers and baths look for at least IPX4.
- Use a fan guard on exposed blades.
5. Fan laws
When speed changes, airflow varies with speed, pressure with speed squared and power with speed cubed. A fan slowed by 20% moves 20% less air and uses about 50% less power, which is why speed-controlled fans save energy.
Frequently asked questions
What is the difference between axial and centrifugal fans?
An axial fan pushes air along its shaft and gives high airflow at low pressure. A centrifugal fan turns air 90°, produces higher pressure and is used with long ducts and filters.
What is the difference between an electric fan and an exhaust fan?
An electric fan moves room air for a cooling effect without replacing it. An exhaust fan removes stale or humid air and lets fresh air in.
How many m³/h should a panel fan deliver?
Multiply the heat loss in watts by 3.1 and divide by the permitted temperature difference. 400 W and 10 K need 124 m³/h; add 20–30% for filter loss.
What exhaust fan diameter does a bathroom need?
100 mm (about 90–100 m³/h) is enough for a standard bathroom of around 10 m³. Use 120–125 mm for larger rooms or ducts longer than 3 m.
What determines fan noise?
Speed, blade diameter and bearing type. A larger fan moves the same air at lower speed and less noise; the label states the level in dB(A).