The Significance of the BTU

In the United Kingdom, there are hundreds of festivals every year that celebrate the days before the internal combustion engine.

This was when steam power drove the industrial revolution.

“Steam rallies” are often held at restored train stations or even at water and wastewater pumping stations where huge triple-expansion steam engines power the pumps that once moved the water. In those days, precise measurements of steam power did not exist, and we all know what happens when too much pressure is applied inside a closed system. HVAC had not yet been invented but steam radiators were commonplace to heat buildings and homes. When determining the size of a radiator, pipefitters used crude and imprecise calculations based on the room’s cubic feet and then adding a certain “fudge factor” as a safety measure. History is still “fuzzy” on the origin of the British Thermal Unit or BTU, but it led the way for early engineers to make great strides in heating. It also led to the invention of air conditioning in the early 20th century. A BTU is simply defined as “the amount of heat required to raise the temperature of one pound of water by one-degree Fahrenheit”. To put that in perspective, an average size candle will put out roughly 80 BTU per hour. Steam radiators are inefficient because it takes a lot of energy to create steam from boiling water. With HVAC it is much more important to have a correctly sized unit. A unit that is too large and transfers too many BTU’s is like using a sledgehammer to kill a fly. An HVAC that is too small will not be able to keep up with the demands of cooling and heating a big room.


a/c worker