The logo, like all images in a responsive theme has max-width:100% and height:auto.
So I’m not sure what you mean by needing additional height. The image should resize to fill width, maintaining aspect ratio of image. So the only thing restricting the size of your logo is the width of the left sidebar.
Specific dimensions are not set by the theme.
You could add height and width to your custom css using this slector
#logo img{
height: …px
width: …px
max-width:auto;
}
But your image is no longer responsive. So when a user resizes their browser, what will happen. In Pure for smaller desktops and ipads, all the stuff down the left ends up at the top. If your logo is too tall, it will look rather odd.