It may not work if the Zillow’s server block being requested through iFrame. (You may check this at your console. Most big websites do block).
There is no way to you do that using an iFrame. But in cases like this, I like to create a pop-up (triggered by a click, so browser will not block). Something like this:
<a id="open_in_popup" href="https://google.com">Open</a>
<script type="text/javascript">
jQuery(document).ready(function($) {
$('#open_in_popup').click(function(e) {
e.preventDefault();
var width = 600,
height = 400,
left = ($(window).width() - width) / 2,
top = ($(window).height() - height) / 2,
url = this.href,
opts="status=1" +
',width=" + width +
",height=" + height +
",top=' + top +
',left=" + left;
window.open(url, "_blank', opts);
return false;
});
});
</script>