No, did not say that. Just stating that there is a huge loss of heat due to evaporation. I strongly believe that you are better off with the cover on as it reduces evaporative losses. I guess you could try it for a week with the cover on and a week with the cover off and (if conditions are the same) see which works better for you. I have done it both ways and find when I leave the cover on during the summer my heatpump almost never runs, but when I leave it off during the day the heatpump has to run more.