I am wanting to exhaust a sealed room (except for air intake and exhaust).
The room is 512 ft3, and due to positioning, orientation, and existing construction, I am restricted to using 6" flexible ducting (I may be able to put rigid sections, but don't want to assume this yet).
The route I have to take to the outside wall is about 15 to 20 feet and will require a number of soft bends, at least 1 x 90 degree bend, and likely 3 x 45 degree bends.
I would like to have the ability to change the air completely once every 3 minutes minimum. My initial simple calculation for my target minimum is 171cfm.
My questions are:
- Given a min requirement of 171 cfm, how can I roughly calculate the fan size I need such that I end up at 171 cfm after accounting for the flexible ducting run?
- My initial search online finds that 6" round duct is capable of handling 100 cfm, is this a different rating, or does that mean that even if I could reach 171 cfm, a 6" duct won't handle it?
- Is there a simple forumla to calculate intake requirements?
- If the required intake size is too large for my application, can I make multiple smaller intakes which add up to the same area as the larger?
- Once I have the target fan size if there is any equipment I then want to place in front of it to pull air through, what do I need to know to calculate the new fan size? For example if it tells me the pressure drop if 42 pascals?
- If that filter equipment has an effective cfm range, do I compare that to my fan's rating before or after calculating the effect of the ducting?
I have tried various calculators such as: https://www.cdicurbs.com/ductcal
The problem is, it asks for things like "Duct Air Flow" in cfm, would this be my desired 171cfm for the room?and in the end, I am not sure I understand how to use these numbers. For example, if I add the numbers in, and it tells me the Friction Loss is .45, would that mean I would convert that to .09 for the 20 foot run (.45 * 20)/100, and add 9% to the cfm of the fan to account for the ducting (this doesn't seem close to right to me)?
The resulting calculation doesn't need to be absolutely exact, but I definitely want to land at or higher than my minimum.
Thank you for any help you can provide, after asking all this I am realizing what a tremendous rabbit hole this is for DIY. I will update as I learn more, or discover new information as I will be continuing to try learn on my own after posting!