First, you should follow bcr229's suggestion to cover the top. If it's open, that's how your heat's escaping. If it's closed and you're still having trouble, add the CHE and see if that works. Only if that doesn't do it, do you close the vents. You'll probably also need to add the heat mat on the warm side to get temps up in the warm side hide. I looked at your last post requesting assistance with heating. Is the ambient room temp still 65 degrees? If so, that's why you have to work so hard to get temps up.