Welcome to our forum.
Another thing that I found fascinating is the amount of energy that is lost due to insulation. In all of the nauseaous debate here and elsewhere about the relative merits of the different approaches to insulating spas, nowhere can I recollect reading anyone expressing an appreciation for the fact that most of the heat loss in a spa is through the cover. The author not only makes the case, but points out quite correctly that the cover is the most likely major component to be replaced in a spa and that if a cheap, thin, poorly sealing cover is selected, the energy usage can go up dramatically
http://www.energy.ca.gov/appliances/2003rulemaking/documents/case_studies/CASE_Portable_Spa.pdf#search=%22ANSI%2FNSPI%206-1999%20%22