The Revenge of the Hot Water Bottle

"Unsurprisingly, there’s little – or actually no – academic research into the energy savings potential of hot water bottles. Instead, in recent years scientists have investigated more sophisticated personal heating devices such as electrically heated desks and seats, radiant heat bulbs, or battery-powered heat pillows.

These alternatives look needlessly complex in comparison to the hot water bottle. .. Nevertheless, these studies show that personal heating sources with similar effects as hot water bottles could save a great deal of energy while maintaining and often even improving thermal comfort. For example, one study revealed that lowering the air temperature in an office from 20.5°C to 18.8°C and giving employees a heated chair to compensate for the discomfort leads to 35% less energy use and consistently higher scores for thermal comfort."

".. the average household energy use for gas heating in Belgium – which has a moderate climate – is 20,000 kWh per year. Assuming that the average Belgian heating system is used for six months per year, daily energy use corresponds to 109.6 kWh per day. This energy could heat roughly 900 water bottles per day – enough to keep the whole neighbourhood comfortable.

Imagine that four household members each use two hot water bottles simultaneously and reheat them every two hours throughout their waking hours (16 hours). Total energy use is then below 4 kilowatt-hours, almost 30 times less than the heating energy consumed by the average Belgian household."