How Effective Are Bathroom Fans And Why Isn't Vented Door Used For Them? - HVAC - DIY Chatroom Home Improvement Forum

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Old 02-08-2011, 01:47 AM   #1
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How effective are bathroom fans and why isn't vented door used for them?

Something like this.

It's spec'd for laundry and furnace closets and some machine rooms.
I made sure my bathroom fan was on, but when the entire house smells like the cleaning chemical I used meaning it isn't venting well.

Just how effective are typical bathroom fans at preventing air from escaping out?


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Old 02-08-2011, 03:21 AM   #2
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1. You do not need a large opening in a bathroom door as pictured. Most if not all bathroom fans have a 4 inch discharge. Measuire the clearance at the bottom of your door. Then measure the width of the door and calculate the square inches. It should be equal or more then the area of a 4 inch round discharge.
My best guess as to why you are smelling up the house with cleaners is that even with the fan running, the large opening is allowing the smell to pass through the door. Or
2. You have a propeller fan in your ceiling which is the wrong type for this application unless you have a blower type. The blower type is needed to push air through 4 inch duct. The propeller fans are for through the wall applications directly to the ouside.

3. If you have a blower type, it may not be strong enough.
The length of the duct has a bearing on blower size as with the cubic area of the bathroom. But because of the differant diets of individuals, You will always have some that leave a stronger odor. This adds a wrench to any calculations as to sizing the blower.
I used a rule of thumb to size a blower. I take the cubic area of the bathroom and double it and use that as a starting point. Next to consider is the amount of time needed to discharge the odors and the run length of the duct. So if you have 20 or more feet of duct with elbows; then that will add considerable resistance to the flow of air. I find through my own experience that a blower rated for 85 cubic feet a minute in a 45 cubic foot bathroom and a duct run of 4 feet does the job if the user of the bathroom is there for 5 minutes minimum.
One thing you need to keep in mind is that when fresh air is entering a bathroom while a fan or blower is running, it discharges part odor and part fresh. This is why I recommend to double the cubic area to size the blower as a starting point. You do not want the next user of the bathroom to notice any odor from the previous user. Good Luck.


Last edited by rjordan393; 02-08-2011 at 11:41 AM.
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