we got hammered with a very wet 15'' plus of snow and poof there goes the power out. Good news the power is on now and after 39 hours without power, the hot tub is at 81 degrees thereby dropping a total of 20 degrees after 39 hours w/o the heater. Outside temp lows were in the 20's and highs were in the high 30's. I not sure which is better thermal or FF but am very happy with my Emerald performance and will be tubbing first thing in the morning.