You’ve heard the energy term “BTU,” but have you ever wondered exactly what it measures? Understanding BTU will increase your knowledge of furnaces—and weight loss.
The British Thermal Unit (BTU) is the amount of energy that is needed to raise the temperature of 1 pound of water by 1°F at a standard temperature and pressure (Illustration 1 [H095]). A pound of water is approximately 16 fluid ounces or about 2 cups. A kitchen match burned end to end produces approximately 1 BTU.
We use the measurement “BTU per hour” to measure the heat input and output of a furnace. A typical furnace or boiler in a cold climate could have an input anywhere from 60,000 to 200,000 BTUs per hour; its output would be a little lower, depending on its efficiency.
BTU and high-efficiency furnaces
Let’s look at how BTU relates to a high-efficiency condensing furnace (Illustration 2 [H096]).
A condensing furnace converts combustion flue steam into water. This condensation, or change of phase, requires 970 BTUs per
1 pound of water. During a cold day, a furnace easily can use 100,000 BTUs of natural gas, which produces approximately 1 gallon (8.33 lbs.) of steam. Condense the pound of steam back into water and you’ll save approximately 8,080 BTUs from going up the chimney.
BTU and weight loss
The calorie, like the BTU, is a unit of measurement. Let’s say Joe Inspector wants to lose 1 pound of body weight. We’ll assume that 1 pound is approximately 3,500 nutritional calories or 13,860 BTUs. To lose weight, Joe must burn more calories than he takes in. He takes up jogging to increase the rate of burn.
Typically, jogging burns approximately 350 calories per hour, so to “burn off” a pound of body weight, Joe must put in 10 hours of
jogging. If he jogs for half an hour each day, that will take 20 days.
Back to the furnace
So, that high-efficiency furnace saves about 2.3 pounds of fat from going up the chimney? Well, not really, but you get the idea. Think about losing a few BTUs the next time you walk up the basement stairs, and you’ll wish that you could burn calories and fat like that furnace.