Calculating the correct CFM (cubic foot per minute) for your bathroom fan is important. We need the capacity of changing or replacing all of the air in our bathrooms 8 times each hour. This will remove the moisture that can lead to mold and mildew.
Large bathtubs and showers can give off a lot of steam - which can be relaxing and enjoyable - but - we don't want that steam to stick around. So how do we get rid of it?
A correctly sized fan will help keep our home comfortable and remove the moisture quickly and effortlessly.
Here's how to calculate the correct numbers, so your fan draws out the extra moisture, but isn't too powerful (making it quite noisy).
First, we need to calculate the volume of the bathroom.
Take the length of the room and multiply it by the width of the room. Take that # and multiply it by the height of the room. ie. 7' width x 10' length = 70. 70 x the height of the room (9' or however high your ceiling is) = 630.
Now take that # and divide it by 7.5. Why 7.5? Well remember how I mentioned our air needs to be exchanged 8 times per hour? Well that works out to being changed every 7.5 minutes.
So 630 divided by 7.5 = 84 I always round up, so that means a fan rated 100 cfm, will be perfect for our bathroom.
Hope this helps keep your bathroom well ventilated so you can enjoy those luxurious hot showers!
How to know which size bathroom fan to purchase for your main bathroom, powder room or ensuite bathroom.
How many CFM do I need for my bathroom fan?
Wondering how to calculate which size of fan you need for your bathroom? For a bathroom with a tub or shower, here's the magic ratio!
Calculate the volume of your bathroom:
Height of the room x length of room x width of the room = total volume.
ie. 8' high x 10' long x 6' wide room = 480 cubic feet.
Now divide the cubic feet by 7.5
480 divided by 7.5 = 64 cfm fan size. Or select the closest available fan size, when in between sizes, always select the higher CFM fan. Meaning, if there is a 50 CFM fan and a 75 CFM fan, select the 75 CFM fan.
There you go!
Jil Sonia McDonald - Interior Designer of Jil Sonia Interior Designs.
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