What Size Exhaust Fan for a Kitchen, Bathroom or Generator Room: 8, 10 or 12 Inch
For most homes the answer comes down to the hole in the wall. As a rough guide, an 8 inch exhaust fan suits a small bathroom, toilet or store; a 10 inch suits a typical home kitchen or a larger washroom; and a 12 inch is the one to look at for food premises, generator rooms and workshops, where there is more air, heat or fumes to move. The MODI MD-HWF60 metal net exhaust fan comes in all three sizes, from KSh 2,100 for the 8 inch. Measure your opening first, then check the room volume against the rough figures below.
Step 1: measure the wall or window opening
An exhaust fan has to fit the aperture you have, or one you are prepared to cut. The MD-HWF60 listing gives these frame sizes:
| Size | Model | Frame (W x H x D) |
|---|---|---|
| 8 inch | MD-HWF6002 | 246 x 246 x 145mm |
| 10 inch | MD-HWF6003 | 290 x 290 x 140mm |
| 12 inch | MD-HWF6004 | 352 x 352 x 140mm |
If you are replacing a louvre pane or an existing fan, measure the clear opening inside the frame and allow room for the fan frame to overlap and be fixed around it. If you are cutting new masonry, the opening is a job for a fundi before the electrician arrives, and it is easier to cut slightly small and enlarge than the other way round.
Step 2: work out the room volume
Multiply length by width by ceiling height, all in metres. A bathroom 2 m by 2.5 m with a 2.7 m ceiling is about 13.5 cubic metres. A kitchen 3 m by 4 m with the same ceiling is about 32 cubic metres.
Then multiply the volume by the number of air changes per hour (ACH) the space needs. The result is the airflow, in cubic metres per hour, you want the fan to remove.
Step 3: typical air changes per hour
The figures below are general rules of thumb used in ventilation planning, not figures from MODI or any other manufacturer. Local building regulations, county public health inspectors and equipment makers may require more.
| Space | Typical guidance (ACH) | Usual size choice |
|---|---|---|
| Bathroom, toilet, small washroom | 6 to 10 | 8 inch; 10 inch for a large or shared washroom |
| Home kitchen | 10 to 15 | 10 inch; 12 inch for a large or busy kitchen |
| Food premises, small restaurant kitchen | 15 to 30 | 12 inch, often more than one |
| Generator room | Set by the generator's own ventilation requirement | 12 inch, sized to the generator maker's figure |
| Workshop, salon, store room | 6 to 10, more where there are fumes | 10 or 12 inch |
Worked example, as general guidance: the 32 cubic metre kitchen above at 10 to 15 ACH needs roughly 320 to 480 cubic metres an hour of extraction. The MD-HWF60 listing does not publish an airflow figure for each size, so you cannot match that number to a fan exactly. In practice, a larger blade moves more air, so when you are between two sizes and the opening allows it, go up a size. In a large or very busy room, two fans spaced apart usually work better than one.
Why a metal net fan suits hot or greasy air
Kitchen steam, cooking fumes and generator-room heat are hard on a fan. According to its listing, the MD-HWF60 is built from iron and copper, with a thickened cast iron airfoil blade rather than a light plastic one, a baked black finish and a safety net cover over the intake. The listing notes that the heavier blade is what suits the fan to industrial extraction, where a plastic impeller can distort in warm air. The net cover also keeps fingers and larger debris away from the blade.
As general guidance, a fan in a kitchen will collect grease. Switch it off at the isolator and wipe the net and blade every few weeks; a clogged blade moves noticeably less air.
Where to place an exhaust fan
- High on the wall. Heat, steam and cooking fumes rise, so fit the fan near the ceiling, ideally close to the cooker or shower.
- Opposite the fresh-air inlet. An exhaust fan can only remove air if replacement air can get in. Place it across the room from the door, a window or a vent, so fresh air is drawn through the whole space rather than straight back out.
- Away from the inlet's short circuit. A fan fixed right next to an open window simply pulls in the same air it just blew out.
- Blowing outside. Discharge to open air, not into a ceiling void, corridor or neighbouring room.
Exhaust fan or wall fan?
The two do different jobs. An exhaust fan pulls air out of the room and pushes it outside, taking heat, moisture and smells with it. A wall fan such as the MODI MD-HWF3001 16 inch wall-mounted fan (45W, 1300rpm, KSh 3,500) moves air around inside the room so people feel cooler, but it does not remove steam or fumes. A hot kitchen often benefits from both: the exhaust fan to clear the air and a wall fan to cool the cook. For cooling a living room or office, see ceiling fan prices and sizing, and for combined fittings, fan light or ceiling fan.
Safety and installation
All three MD-HWF60 sizes run on 220 to 240V, 50/60Hz mains. As general guidance:
- Have a qualified electrician wire the fan, with a switch or isolator so it can be turned off for cleaning. In bathrooms, keep the fan and its switch out of the reach of the shower and water spray.
- Fix the frame firmly into masonry or a solid window frame so the fan does not vibrate loose.
- In a generator room, an exhaust fan helps remove heat, but it is not a substitute for the generator's own exhaust pipe. Engine exhaust gases, including carbon monoxide, must be piped outside, and the room must meet the generator maker's ventilation requirement.
Where to buy
The MD-HWF60 and the MD-HWF3001 wall fan are in our fans collection. You can collect from our Nairobi trade counter at Royal Business Park, opposite Complast, Old Mombasa Road, Monday to Saturday, 8:00 to 17:30, with free pickup. Or order for countrywide delivery at a flat KSh 350, free on orders over KSh 15,000. Contractors fitting out several kitchens or washrooms can buy by the carton; request a trade quote on our trade page. For help choosing a size, message us on WhatsApp with your opening size and room dimensions.
Common questions
What size exhaust fan do I need for a bathroom?
For a typical home bathroom or toilet, an 8 inch fan is the usual choice, with a 10 inch for a large or shared washroom. Check that the 246 x 246mm frame of the 8 inch MD-HWF6002 fits your opening.
How much is an exhaust fan in Kenya?
The MODI MD-HWF60 8 inch exhaust fan is KSh 2,100 a piece. The 10 and 12 inch sizes are listed on the product page, with carton prices for trade buyers.
How much power does an exhaust fan use?
The 8 inch MD-HWF60 is listed at 26W, and the range runs on 220 to 240V, 50/60Hz mains. As general guidance, a draw of that size is modest next to a kettle or cooker, though the exact cost depends on your tariff and how many hours the fan runs.
Can I fit an exhaust fan in a window?
Yes, if the window can take a fixed panel with an opening matched to the fan frame. Measure the clear opening against the frame sizes in the table above and have the panel cut and fixed securely before the fan is wired.