I generally only recommend ERVs for very airtight homes (less than 2 ACH50), and in those cases balanced ventilation is the ONLY way to exhaust from bathrooms. More coming on that for those who are scratching their heads.
If you DO need an ERV or HRV (hear the difference at https://www.youtube.com/watch?v=QOe4lluGwCg) then where do you put the supply and exhaust ports? How many CFM should they each push and pull? Here's my simple breakdown of what you'll need to consider.
FYI, supply fresh air should be ducted into the central duct system before the main filter, or independently ducted to bedrooms or common spaces (EITHER a supply or extract in each room, rarely both or neither).
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