Re: Bathroom Exhaust Fan - help with problem
When taking a shower .... adding warm water vapor and mixing with the relatively cooler air into a room will create condensation..... it's the law of nature.
So for benefical reasons this moisture needs to be mechanical exhasted ( vented ) and usually done by a bathroom exhaust fan.
The biggest mistake people make is not running the fan for at least 20 minutes after to continue removing the excess humidty introduced by the shower.
Bathroom fans connected to light switches start running when the light is turned on. In this situation users turn the light off before all the moisture is exhausted after a bath or shower.
Use a delayed fan shut-off to keep the fan running for 20 minutes after you leave the room. You can use electronic or mechanical timers or humidity sensors .... or a combination of both .... to control the fan.
Many people have the misconception these fans will remove this condensation immediately. Unless you have a huge industrial sized exhaust system this will never happen .... rather the bathroom exhaust fan will be removing a portion of this condensation during the duration of the shower.
Unless you have a thick cloud of condesation it's likely the fan is working .... how well and how much it's exhausting is something that needs to be determined.
There are guidlines that have been established by the Home Ventilating Institute ( HVI ) determinig the ventilation of bathrooms. Basically this recommends how many cubic feet per minute ( CFM ) of air should be vented for the size and number of fixtures for the bathroom.
Venting the air out using a bathroom exhaust fan also requires the same amount of air to be replaced .... known as air exchange. If this doesn't occur the exhaust fan wouldn't work very well.
The HVI recommends 1 CFM per 1 square feet for the bathroom venting.
They also recommend considering the number of fixtures toilets , tubs , showers for large bathrooms over 100 square feet based on the following :
toilet = 50 CFM
Shower = 50 CFM
Bath tub = 50 CFM
Jetted tub = 100CFM.
These values are determined with a recommended 8 air exchanges per hour.
Based on the size of your bathroom ..... 11x15 = 165 square feet.
This would mean the bathroom fan would need to be rated at 165 CFM .
In situations such as this it's recommended to use 2 bathroom fans . Common sizes of bathroom fans range from 50 CFM - 100 CFM with the larger placed near the shower and the smaller could located near the toilet ... for example.... or at least one fan 150 CFM.
As the previous poster mentions there may be issues with restrictions for air flow that should be checked.
Ducting can affect fan performance..... uninsulated, undersized, or droopy flex ducting, ineffective or dirty backdraft dampers and exhaust louvres can cut rated airflow by more than 50 per cent.
Straight short duct runs with few turns will provide highest air flow.
For bathroom fans use duct with a diameter of at least 4 in. For long runs use larger diameter 6 inch to improve air flow. It is usually best to avoid fans with 3 inch exhaust ports and ducts.
To find out if your exhaust fan is drawing air ........... hold a piece of toilet tissue up to the grill. The exhaust air should hold the tissue tightly to the grill. You could also check the outlet to make sure the air is leaving your house.
Yikes ... this post is getting long winded.
Hope this helps.
"" an ounce of perception -- a pound of obscure "