How Our Bodies Stay Comfortable
Our bodies act like miniature furnaces, continuously throwing off surplus heat. The amount of heat we produce varies with our age and activities.
A young person throws off more body heat than an elderly one, and anyone gives off more heat when walking than when sitting, more when running than when walking. Heat always moves from a warm surface to a colder one. Whether we feel warm or cold depends upon whether our surroundings are warmer or colder than we are.
Actually, our bodies constantly produce more heat than they need. For comfort, they must be able to transfer this heat to surrounding objects, or to the air, at a balanced rate. If we don't lose heat fast enough, we feel hot. If we lose it too fast, we feel cold. In between, we're comfortable.
If we are to be comfortable, our skin temperature must remain relatively constant whether we are active or resting, whether it is winter or summer. Our clothes are designed to maintain the first phase of balance... and our houses should complete the process.
In a house whose exterior surfaces are insulated and weatherstripped, we lose less body heat to those surfaces because they are warmer. Because we lose less body heat, we feel more comfortable and cozy in a house that is cooler.
A house that is properly "buttoned up" is comfortable at 65° to 68°. A poorly weatherstripped, inadequately insulated house requires a temperature of about 3° more.