Zillow is a good web site to search for homes for sale.  However, Zillow does a poor job of valuing a home.  The reason is simple -  Most times Zillow doesn't have enough information to make an accurate value assessment.  

Below is an excerpt from an article from Inman News:

"In my opinion, the biggest issue with the Zestimate is its inability to take into account items such as home features, upgrades and the condition of a property. Those items require an actual human to take an in-depth look at your property and determine how it truly compares to another property. Once that determination is made, proper adjustments to the value are made.

I’m not here to bash the Zestimate. It works OK for general property value estimates, especially when the home is in a subdivision of similar homes. A home is most likely the single largest item you will sell in your lifetime. Do yourself a favor and do not use the Zestimate as a pricing tool for your home — it could end up costing you tens of thousands of dollars."

You will be better served using data from a local Multiple Listing Service and a local real estate Broker.