The energy saved in turning the thermostat down overnight is examined. The model for the house is a 1500‐ml water‐filled beaker. The beaker is in an ice–water bath. The energy required to maintain the beaker atTH(20 °C),TL(15 °C), and to raise the temperature fromTLtoTHis determined. Times to cool and heat are noted. The data are extrapolated to fit typical house situations, and resultant energy savings are shown.