Environmental controls affect weight gain but, to what extent? Outsourcing your thermodynamic equilibrium to a heater reduces the work your body must do to achieve it; much like outsourcing your motion to a car. Whether a house is heated by a furnace or a human body by chemical reactions, the principle is the same: to sustain a certain temperature, the heat (energy) expenditure must equal heat outflow.
where m is the mass of the object, c is the specific heat capacity, ΔT and ΔQ are changes in temperature and energy respectively. Let’s compute the energy required to maintain normal human body temperature (~ 37°C). To that end, a couple of naïve yet reasonable assumptions are made:
- The human body is basically water. Specific heat capacity of water is 1 cal/g/°C;
- The body is not receiving significant heat from direct sources, e.g. the Sun, fire place, another body.
Last piece of the puzzle: temperature change. How many degrees, say, per hour, does a human body lose and must therefore burn chemical fuel to compensate? Don’t know. We do know how many degrees a dead body loses per hour, approximately. We know this because forensic science measured it. A chemically dead body stops producing heat, therefore its initial heat loss is roughly the heat required to keep it alive. Quick search reveals the temperature difference associated with said loss to be ~ 1°C per hour under normal conditions (forensic science is not Accounting, normal means the [dead] body was not found at the North Pole or the engine compartment of the Titanic). Consequently, the energy required to just keep a 70kg (154lbs) body at the correct temperature is ~ 70 food calories per hour, ~ 1,680 food calories per day (1 food calorie = 1,000 calories = 1 kcal). This is not far from the recommended daily intake of 2,000 kcal, because vast majority of us don’t do much but keep our bodies at the appropriate temperature.
What’s In It For Me?
So we spend an obscene amount of energy maintaining thermodynamic superiority over our environment; how is this illuminating? It can be shown using Newton’s Law of cooling that if the normal temperature (20°C, 68°F) is lowered by 5°C (9°F), one’s body has to expend ~ 30% more energy to stay alive (60% for 10°C, relationship approaches linear). For a 70kg individual: additional 20 kcal per hour, almost 500 kcal per day, which is equivalent to a one hour jog.
In natural sciences, this is known as the Spherical Cow Analysis, making unrealistic assumptions to approximate the reality. Because the human body is not all water suspended naked in still air for twenty-four hours on a cloudy day — values derived here are estimates and may differ from reality by a factor of three or so in either direction. That said, they represent a good quantitative conclusion. The less [thermodynamically] comfortable you are, the more energy you burn. That extra amount is not marginal, it is significant and measurable.
Backup Food Supply (a.k.a. fat) → $$$
Want to lose excess fat – turn off your heater and wear less clothes in cold weather. It should be noted that cooling a human body (i.e. sweating) takes a non-trivial amount of energy – so turn off your A/C as well.
False Metrics 