It depends on the enclosure. A top opening like found on tanks is very inefficient. Enclosures like vision or AP for example are many times more efficient they hold heat for a while. If you add insulation it can change that even more. I have enclosures in a cool room (below 68ºF most of the time) and with insulated enclosures hot side and cool side UTH as well as a interior Fluorescent light and deep blue led lights I hold temps with minimal power usage. Even during a power failure I loose about one degree an hour. Most of the time the my herpstats are showing 0% power and sometimes kick in to 10-20% I cut my power bill down by 60% even adding 4 enclosures it was not even as high as it was with two and lamps. (I now have 11 and still save cash.)