***and where does the air come from that replaces the "90 degree" air from inside the cabinet... the "15 degree" air no? The blown air doesn't get heated in either case***
Of course the air from outside of the cabinet eventually ends up inside... it's not "sealed", but the blower takes a LOT longer than 1 second as someone suggested to use up all of the warm air within the cabinet. (certainly you MUST be joking!)
I definitely agree that HS has one of the best systems for this I've seen on that type of spa... HS has one of the best engineered tubs on the market.
I can run a thermospa for 30 minutes, then remove a panel, and the inside air is a LOT warmer than the outside air! I'm guessing it's still well over 70 degrees! (I'm going to test this with a thermometer)
As far as someone saying the blown air doesn't get heated, it may not get heated "directly", but with a thermopane tub the pumps, heater and blower all constantly create heat, (as shown in Chas diagram) and it warms the air inside of the cabinet.
Keep in mind as well, that the heater is heating the water, and the 103 degree water temperature also aids in warming this air, before it enters the blower.
Z