It's good to keep in mind that heat loss depends on the temperature difference (Newton's law of cooling). When it's 15°C outside, heating to 16°C will take ~1/

It's good to keep in mind that heat loss depends on the temperature difference (Newton's law of cooling). When it's 15°C outside, heating to 16°C will take ~1/16 the energy that it takes to heat to 16°C when it is 0°C outside.