Hi All:
First time poster trying figure out what duct size I should use for an inline bathroom exhaust vent.
I did the math: I have a 512 cubic ft bathroom, actually two of them. and with the ACH of 8 I need a 68 CFM exhaust fan.
An Inline is what I want to use for the low sound.
I'm having difficulties trying to match the needed CFM's with the required duct diameter. The flex duct charts online show that a 68CFM duct should be well really 5.5 inches at SP of .05, since there aren't any ducts of that size the size jumps to 6 inches (75CFM).
I can't seem to find any inline exhaust fans with a rating near 68 CFM and a duct size of 6 inches.
Air King rates their units at a Static Pressure of .2. I think its because of the elbows and vertical lift to the roof exhaust vent. I'd will be venting under the eves with an eves vent.
Now, it just seems strange to me that a 190 CFM exhaust fan at .2 SP would require a 6.5 inch duct diameter but is fashioned with a 6 inch diameter opening.
In my configuration I don't think my SP will be .2 , more likely it will be lower as I will only have a couple of bends and 1 elbow pointing down towards my eves. Probably no longer then 12 ft of flex.
So I'm left confused, is 190 CFM at .2 SP the same as 100CFM at .06 SP?
What I am afraid of is oversizing the exhaust fan and drawing fumes from the waste pipe. That happened when an installer screwed up the return size on our AC system. That was bad, they placed an undersized return right next to the washing machine and it started pulling fumes right from the drain of the washing machine. -nightmare, do not wish to do that in as I want to place the grill directly over the shower.
Hope this is enough info for someone to help me out.
Thanks in advance
-pauli
First time poster trying figure out what duct size I should use for an inline bathroom exhaust vent.
I did the math: I have a 512 cubic ft bathroom, actually two of them. and with the ACH of 8 I need a 68 CFM exhaust fan.
An Inline is what I want to use for the low sound.
I'm having difficulties trying to match the needed CFM's with the required duct diameter. The flex duct charts online show that a 68CFM duct should be well really 5.5 inches at SP of .05, since there aren't any ducts of that size the size jumps to 6 inches (75CFM).
I can't seem to find any inline exhaust fans with a rating near 68 CFM and a duct size of 6 inches.
Air King rates their units at a Static Pressure of .2. I think its because of the elbows and vertical lift to the roof exhaust vent. I'd will be venting under the eves with an eves vent.
Now, it just seems strange to me that a 190 CFM exhaust fan at .2 SP would require a 6.5 inch duct diameter but is fashioned with a 6 inch diameter opening.
In my configuration I don't think my SP will be .2 , more likely it will be lower as I will only have a couple of bends and 1 elbow pointing down towards my eves. Probably no longer then 12 ft of flex.
So I'm left confused, is 190 CFM at .2 SP the same as 100CFM at .06 SP?
What I am afraid of is oversizing the exhaust fan and drawing fumes from the waste pipe. That happened when an installer screwed up the return size on our AC system. That was bad, they placed an undersized return right next to the washing machine and it started pulling fumes right from the drain of the washing machine. -nightmare, do not wish to do that in as I want to place the grill directly over the shower.
Hope this is enough info for someone to help me out.
Thanks in advance
-pauli