Step 1: Room volume
Multiply the length, the width and the height of the room in feet to get the volume in cubic feet. A bathroom of 5 x 8 ft with a 9 ft ceiling is 360 cubic feet, and a kitchen of 10 x 12 ft with a 9 ft ceiling is 1,080 cubic feet.
Step 2: Air changes per hour
Choose how often the room air should be replaced. As a rule of thumb, bathrooms need about 8 to 10 air changes an hour, and kitchens about 10 to 15, more with heavy frying.
Step 3: Convert to airflow
Airflow in cubic feet per minute is volume times air changes divided by 60. For the bathroom: 360 x 8 divided by 60 is about 48 CFM. For the kitchen: 1,080 x 12 divided by 60 is about 216 CFM. One CFM is about 1.7 cubic metres per hour, so these are about 82 and 367 m3/h. Check the rating on the box and choose a fan that delivers at least this, allowing for duct losses.
Fan diameter as a rough guide
A 4 to 6 inch fan usually suits a small bathroom, 8 inch suits a larger bathroom or a small kitchen and 10 to 12 inch suits a larger kitchen. Always check the airflow rating, because two fans of the same diameter can move very different amounts of air.
Ducts, shutters and noise
A long or bent duct cuts airflow, so keep it short and straight, and use a fan rated for ducts. A shutter or jali stops backdraft and insects. Noise falls with larger, slower fans and with BLDC motors. Fix the fan firmly and seal around it. Vibration travels through thin walls, so use rubber washers where the fan meets the frame, and check that the blades are clean and balanced, since dust makes them noisy. Fit the duct with a slight downward slope towards the outside so that condensation drains away from the fan.
Kitchens: fan or hood
For cooking smoke and grease, a hood over the hob captures more at the source than a wall fan. See exhaust hoods and kitchen hoods.
Bathrooms: placement
Place the fan high on an outside wall, away from the door, so that air crosses the room. Leave a small gap under the bathroom door, or fit a grille, so that fresh air can enter and the fan does not pull air through the keyhole and the window gaps. Run the fan for about 20 minutes after a shower, and use a timer switch if people forget to turn it off. Inner bathrooms need a duct to the outside. See bathroom design.
Prices and installation
Indicative market ranges are about PKR 2,300 to 3,500 for window fans, from about PKR 2,800 for slim BLDC fans and from about PKR 4,000 for duct fans. Fit with a licensed electrician. See electrical fittings in Pakistan.
Frequently Asked Questions
Work out the volume, use about 8 to 10 air changes an hour and convert to CFM. A 5 x 8 ft bathroom needs about 48 CFM, so a 4 to 6 inch fan with a suitable rating is usually enough. Ask for the specification in writing so you can compare quotes on the same basis.
A 10 x 12 ft kitchen at 12 air changes needs about 216 CFM, so choose an 8 to 12 inch fan with a suitable rating, or a hood over the hob. Check the warranty terms and who honours them before you pay.
Multiply CFM by about 1.7 to get cubic metres per hour. Measure carefully and confirm sizes with the supplier before ordering. If in doubt, send a photo and the measurements and we will advise.
Yes. Long or bent ducts reduce airflow, so keep them short and straight. If in doubt, send a photo and the measurements and we will advise. Ask for the specification in writing so you can compare quotes on the same basis.
Choose a larger, slower or BLDC fan, fix it firmly and seal the duct and the opening. If in doubt, send a photo and the measurements and we will advise. Ask for the specification in writing so you can compare quotes on the same basis.
Send the room size and use on WhatsApp. We confirm what we can supply and reply with a written rate. Ask for the specification in writing so you can compare quotes on the same basis. Check the warranty terms and who honours them before you pay.
Send the room size, the items you need and a photo of the space on WhatsApp. We confirm what we can supply and reply with a written rate that lists every item with its model and quantity, so you can compare quotes from different suppliers on the same scope.