The Effervescence theme uses the following to control the image size:
(getCustomImageURL(550, null)

How can I change it, to only control the height?
I want for example the maximum height to be 600. I don’t care much about the weight!

How can it be done?
I tried the following without success:
(getCustomImageURL(600, 800)
(getCustomImageURL(800, 600)

Our functions are described in the document found here: http://www.zenphoto.org/documentation-official/zenphoto/_template-functions.php.html

As you can see from the description of the getCustomImage parameters, the first parameter is the image size, the second the with, and the third is the height.

What you want to do is getCustomImage(null, null, 600);

Thanks it works perfectly.