question with heloc appraisals

[Mitchell Litam]

Hey guys. Trying to secure on Heloc on my home to help secure funding for a BRRRR.

I recently did a cash out refinance to buy my business partner out a year ago.

How do banks typically do appraisals.

I own a duplex (Does this get valued differently by banks as opposed to single family homes?) and owe about $140k on it.

The city just raised my property value to about $126 and I tried to dispute it to keep property tax lower.

Zillow says my zestimate is about $269k with single family homes within two houses selling for $250k and 300k in the last 6 months. Again not sure how much it affects that those were single family homes and mine is a duplex.

Can anyone help me understand the appraisal values and how they may run the numbers on them? I am trying to work with Third Federal Bank if that helps.