The answer is setting the temperature down is more energy effiecient and hence cheaper then keeping the tub a constant temperature. This is actually a first year physics problem routinely given to explain "work". It's a fact, there really isn't any question about it. This is the reason home thermostats are now programable, you save lots of money over time by turning down the heat while your not there, in bed, etc. Of course having to go out to the tub an hour ahead of jumping in doesn't seem worth while to me. We're at a constant 102!
Not necessarly. The variables include: how much you are dropping and raisng the temperture.? A well insulated spa will see less of a drop in temp and thus requiring less energ/work to return it to it's desired temp ie: how quickly are you loosing heat?
Also consider the The volume of water your are heating and how often you are bringing it back up to temp.
The efficently of the heater is also a significant factor.
I feel the home programable thermostat analogy is abit deciving as home thermostats are part of a larger zoned system that is heating the air (air heats quicker and cheaper than water)in a larger space, with multiple rooms that may or not be used. Plus, a sweater is ok if the room has a bit of a chill. I wouldn't recomend cashmire in the hot tub.
I had an older ineffeinct tub and tried to save a few bucks by bringing down the temp a few degrees and it resulted in the heater and pumps doing more work than simply maintining a constant temp. Your most expesive times to run a heater and pump is upon start up. Energy consumption spikes on start up. With some pumps, getting the pump spining takes more energy than running it for several hours.
Unless you are going to be away for a significant time, dropping the temp and raising it, wont save you any money and will probably cost you a few cents.
