Is a over-rated bathroom exhaust fan bad?

[Billy2K]

Hey guys,

I picked up a Broan exhaust fan that does 90 cfm, and 1 sones, so it's pretty quiet and powerful. My concern is that it might be too powerful for what I need. The bathroom is around 60 sqft, it has the basic tub, toilet, and sink.

Would the exhaust fan start sucking air from heating vents and pull in carbon monoxide?

[alloroc]

no

... unless you had a cracked shell in your heat exchanger.

[badatusrnames]

Originally posted by Billy2K
Hey guys,

I picked up a Broan exhaust fan that does 90 cfm, and 1 sones, so it's pretty quiet and powerful. My concern is that it might be too powerful for what I need. The bathroom is around 60 sqft, it has the basic tub, toilet, and sink.

Would the exhaust fan start sucking air from heating vents and pull in carbon monoxide?

Are you crazy!? Ever heard of fan death? It's become an epidemic in Korea.

Make sure you leave the door slightly cracked open if you're in there for a while dropping a big one. Or else you'll basically die due to several mechanisms:

-An electric fan creates a vortex, which sucks the oxygen from the enclosed and sealed room and creates a partial vacuum inside.

-An electric fan chops up all the air particles in the air leaving none to breathe.

-The fan uses up the oxygen in the room and creates fatal levels of carbon dioxide.

-If the fan is powerful enough, it will suck all the air away, preventing one from breathing.

-The fan will contribute to hypothermia, or abnormally low body temperature by enhancing room cooling.



But man, if you've got carbon monoxide being emitted by your heating vents, I think you've got far larger things to worry about.

[alloroc]

I'm sorry .. let me fill you in more.

Ashrae ventilation standard 62.2

AHRAE Standard 62.2 fan sizing is based on the total square foot of a home and number of bedrooms.

Formula: (Total square foot of a home/100) + (Number of bedrooms + 1) x (7.5 cfm).

Example: 2500 square foot home with 3 bedrooms: (2500/100) + (3+1) x 7.5 = 25 + 30 = 55 cfm.

You get this if you have a newer home with a 'ventilation' switch. Chances are the exhaust fan moves more than AHRAE's recommended minimum which is fine because there is "make up" air supplied to the house from the main heater fan in this instance to accommodate the exhaust fan.
- Thus keeping the total house air pressure more or less neutral so let us ignore the continuous fan option ;P

Now ...
On Demand Local Exhaust
ASHRAE 62.2 requires each room that creates contaminants (bathrooms, kitchens, art studios, etc.) must have some type of exhaust that clears the air to the outside of the home.
So .. in the example above a continuously running fan of 55 cfm in the bathroom would be adequate.


Intermittent Local Exhaust
If a local exhaust fan (bathroom fan - kitchen range hood) is to be on 35% to 60% of the time the CFM can be multiplied by a factor of 2 or 110CFM
If a local exhaust fan (bathroom fan - kitchen range hood) is to be on 0% to 35% of the time the CFM can be multiplied by a factor of 3 or 165 CFM.

So in short 100 cfm seems to be perfect balance between airflow and comfort level and economy for any house - especially here where we have basements that are not part of ASHRAE's consideration.

[alloroc]

... not to mention that those fans airflows are measured with minimal static loss (ductwork) and as soon as you add any extra static the airflow will diminish.

[89s1]

Originally posted by badatusrnames


Are you crazy!? Ever heard of fan death? It's become an epidemic in Korea.

Make sure you leave the door slightly cracked open if you're in there for a while dropping a big one. Or else you'll basically die due to several mechanisms:

-An electric fan creates a vortex, which sucks the oxygen from the enclosed and sealed room and creates a partial vacuum inside.

-An electric fan chops up all the air particles in the air leaving none to breathe.

-The fan uses up the oxygen in the room and creates fatal levels of carbon dioxide.

-If the fan is powerful enough, it will suck all the air away, preventing one from breathing.

-The fan will contribute to hypothermia, or abnormally low body temperature by enhancing room cooling.

Especially point #2