1 cfm per square foot. Not. [1]
Seed Eco-Home Floor 1 has a 5x9 bathroom = 45 sf.
Not! The code requirement is a minimum of 20 cfm continuous, or 50 cfm intermittent. IRC - [M1507.4] - [2]
- Continuous means running 24/7
- Code does not stipulate bathroom size.
Ducts are very specific - 3" smooth for 50 CFM is required, foil ribbed is not allowed at 50 CFM Table M1506.2 - Not! This is only for whole house systems
- Section M1507.2 [3] covers local exhaust fans, including bathroom. It stipulates only exhaust rates, not vent material.
- Does vent material matter?

Controversy

Bathrooms with bath facilities require minimum of 80 CFM here [4]. It states pursuant to table M1507.3, which is not found in IRC 2020 or IRC 2016. Must be an older code?

Bath Vent Codes