Good question. I know that they are incredibly efficient because mine will run off the grid at the ranch, so that was important. I purchased mine from Reptile Basics and am really happy with it. I know that they have high BTU per watt efficiency- just don't know what it is! Also, I only need my Helix to be set at 87F.
For the specifics of your question, we ought to call Rich. I'll shoot him an email shortly.