How do I determine my HELOC amount?

[Katie Hole]

Hello! My husband and I are just starting out in Real Estate Investing. We are working on gathering funds for our first rental property. We have lived in our current home for 4 years now and would like to take a HELOC out to pay for our first property. My question is, what website do banks use to determine the price of your property? We tried a couple months ago and the bank told us our home went down in value since we bought it. We find this totally crazy since our neighborhood has similar houses selling quickly at higher rates. I know Zillow is high. We want to check it out before we head to the bank. Thanks in advance for any advice!