It basically becomes a greenhouse if you have windows, and of course the windows have three layers which prevents the precious warm air to leak out. Also the roof is black metal. You basically don't need to have the heater on if it's a sunny winter day - because the heating from the sun.

The biggest problem though is the dryness during the winter, cold air comes in and expands, lowering the relative humidity, warm moisturous air is pushed out by mechanical fans. You get extreme dryness, lower then in the desert, which is not good for mucus membranes. I believe that if we could revolutionise air conditioning systems we could prevent the next pandemic (and maybe help the global climate).