BOTANVÈVentilation Fan Size Guide
Sizing a ventilation fan is a three-step job: work out the airflow the room needs, choose a duct diameter that carries it quietly, then pick a fan whose airflow at your duct's static pressure meets the requirement. This guide walks through the numbers with VENTS TT and VKMz inline fans as the examples.
Step 1 — airflow from air changes per hour
Airflow (m³/h) = room volume (m³) × air changes per hour (ACH). Divide by 1.699 for CFM.
| Space | ACH | Example |
|---|---|---|
| Bathroom 2.5 × 2 × 2.8 m | 10 | 14 m³ × 10 = 140 m³/h (82 CFM) |
| Domestic kitchen 4 × 3 × 2.8 m | 15 | 33.6 m³ × 15 = 504 m³/h (297 CFM) |
| Office 6 × 5 × 2.8 m | 6 | 84 m³ × 6 = 504 m³/h (297 CFM) |
| Small shop 8 × 6 × 3 m | 8 | 144 m³ × 8 = 1,152 m³/h (678 CFM) |
TT series vs VKMz series — which to choose
The VENTS TT is a compact mixed-flow fan with a relatively simple design, suited to short duct runs (up to approximately 3–5 metres of straight duct with one or two bends) in residential and light-commercial applications — bathrooms, kitchens, small server rooms. It generates moderate static pressure.
The VENTS VKMz is a centrifugal fan (squirrel-cage impeller) that develops significantly higher static pressure, making it suitable for longer duct runs, multiple bends, grilles with high resistance, or commercial kitchens where extraction rates are high and the duct run is extended. If you are unsure, use the duct / CFM calculator to estimate the static pressure your duct run requires — if it exceeds approximately 100 Pa, choose the VKMz.
Ventilation requirements in UAE buildings
Dubai Municipality, Abu Dhabi Quality and Conformity Commission (ADQCC), and local civil defence authorities set minimum ventilation rates for commercial kitchens, bathrooms and occupied spaces. For residential bathrooms, 8–10 air changes per hour is typically required. For commercial kitchens, requirements start at 15 ACH and can reach 30 ACH or more depending on cooking type. Always confirm with the relevant authority before specifying ventilation for a permit-requiring fit-out.
Use the duct / CFM calculator to run your own numbers. Commercial kitchens and other regulated spaces must follow municipality / Civil Defence rates.
Step 2 — duct diameter
Duct area = airflow ÷ velocity. At 800 FPM (about 4 m/s) a 100 mm duct carries roughly 100–130 m³/h, 125 mm about 170–200 m³/h, 150 mm about 250–300 m³/h, 200 mm about 450–550 m³/h, 250 mm about 700–850 m³/h and 315 mm about 1,100–1,300 m³/h. Higher velocities carry more but add noise.
Step 3 — choose the fan
| Model | Duct | Max airflow | Power | Type |
|---|---|---|---|---|
| VENTS TT 100 | 100 mm | 187 m³/h | 33 W | Mixed-flow, 2-speed |
| VENTS TT 125 | 125 mm | 280 m³/h | 37 W | Mixed-flow, 2-speed |
| VENTS TT 150 | 150 mm | 520 m³/h | 60 W | Mixed-flow, 2-speed |
| VENTS VKMz 100 | 100 mm | 250 m³/h | 62 W | Centrifugal, galvanised |
| VENTS VKMz 150 | 150 mm | 455 m³/h | 64 W | Centrifugal |
| VENTS VKMz 200 | 200 mm | 1,000 m³/h | 144 W | Centrifugal |
| VENTS VKMz 250 | 250 mm | 1,070 m³/h | 152 W | Centrifugal |
| VENTS VKMz 315 | 315 mm | 1,540 m³/h | 185 W | Centrifugal |
'Max airflow' is at zero static pressure. Real installations with 3–6 m of duct, a bend and a grille typically deliver 60–75% of the maximum, so size the fan with margin. TT mixed-flow fans suit short, simple runs; VKMz centrifugal fans hold their airflow better against longer runs and filters. VENTS prices are quoted on request.
Common mistakes
- Choosing a fan by maximum airflow without allowing for duct resistance.
- Undersized duct (a 100 mm duct on a 150 mm fan strangles it).
- Long flexible duct runs with sagging — use rigid duct where possible.
- No make-up air path — an extract fan cannot remove air that cannot be replaced.
Frequently asked questions
What size fan for a bathroom?
A 100 mm inline fan (VENTS TT 100 or VKMz 100) covers most UAE bathrooms up to 10 ACH.
TT or VKMz?
TT for short straight runs and lowest cost; VKMz for longer runs, filters or higher static pressure.
How do I convert m³/h to CFM?
Divide by 1.699.
Why are VENTS fans priced on request?
Stock and pricing vary; WhatsApp us the model for the current price and lead time.
Related products & pages
This guide is general information based on BOTANVÈ catalogue data and widely published HVAC-R practice. It is not a substitute for the equipment manufacturer's installation manual or the advice of a qualified engineer. Prices and availability change; the product page is authoritative.