Wordpress featured image size uniform height

I am setting featured images to posts, and displaying a default image if one isn't set. My code is here...

 <?php if ( has_post_thumbnail() ) {
 the_post_thumbnail( 'full', array( 'class' => 'img-responsive' ) );
 } else { ?>
 <img src="default-image.jpg" class="img-responsive" />
 <?php } ?>

Problem is simple. All of the images are different heights. I want them all to be uniform height so my bootstrap grid lines up evenly.

Any thoughts? Lots of examples online but none work with featured image AND default image.