What Makes the Btu British?

Published: November 6, 2018 - by Dan Holohan

Categories: History Lesson, Darn-Good Stories, The Business of Heating, Educational Opportunities


And why isn’t there a Ctu?

You know, a Canadian thermal unit? It has a nice homegrown ring to it, doesn’t it? Feel free to adopt it if you’d like, and give it any value you please. You won’t be the first.

The Btu, this thing we can feel but not see, has quite a history. And seeing as the British are supposed to be using the metric system these days, they’re mainly using calories instead of Btu, so why shouldn’t you be able to rename it to something closer to home? Hey, Thomas Tredgold did.

Which brings me to an old friend. John Woodworth was the guy I read in the trade magazines when I was growing up. I’d write to him with comments and questions about his articles, and when I became a writer in the magazines we became good friends. When he retired from the Hydronics Institute some years ago, he gave me a tattered text with a broken spine and a publication date of 1836. The title was Warming and Ventilating of Public Buildings and I slobbered all over that book because I am a student of history. It’s author, Thomas Tredgold, the man who gave us the Btu, had published the first edition of that text in 1824. My gifted copy from John was the Third Edition, and on page 24 I found these delicious words:

"In order to compare the effects of different kinds of fuel, some convenient measure of effect should be adopted: not only for the purpose of lessening the trouble of calculation, but also to render it more clear and intelligible. I shall, therefore, without regarding the measures of effect employed by others, adopt one of my own, which I have found useful in this and other inquiries of a similar nature. I take as the measure of the effect of a fuel, the quantity, in pounds avoirdupois, which will raise the temperature of a cubic foot of water one degree of Fahrenheit's scale."

Thomas Tredgold was a railroad engineer who dabbled in heating buildings. Steam locomotives had been in England for just 20 years when Mr. T first published his book, and there were some steam-boiler explosions that the early adopters had to deal with.

Well, actually there were a lot of steam-boiler explosions that they had to deal with, so Mr. T figured it would be good to have a better way of measuring heat energy. And so arrived the British thermal unit, and by way of that tattered text that I held in my hands.

But take a closer look at what he wrote all those years ago. He said that his new unit of measurement would be the amount of heat it took to raise one cubic foot of water one degree Fahrenheit, not one pound of water, as it is today.

So why the change? Hmm.

Mr. T goes on in his book to give examples of how much fuel it would take to bring a cubic foot of water to a boil from several different temperatures. He explained about latent heat, and how we have to add a lot of that to get water excited enough that it changes from liquid at 212°F to steam at that same temperature on Gabriel Fahrenheit’s scale. He covers all the bases, and in a delightfully British way.

But I keep smiling about that change from one cubic foot of water to one pound of water in the definition. Why the change? I’ve never been able to track down the exact answer, so I speculate. I figure the term got changed for one reason and one reason only: Mr. T had assumed ambient temperature on the Fahrenheit scale. And once he was gone, all bets were off. Those who followed him could change anything that he had to say because he had just made it all up in the first place. There is nothing holy about a Btu. If he could make it up, others could change it, and Mr. T was no longer around to waggle his British finger at them.

So there.

But what does it matter? Let's face it; the original Btu came out of one guy’s imagination. The British thermal unit could have been anything. What mattered was that enough people got on board and agreed to use his term and not someone else’s term. Or to change it once he was dead to something else.

The point was that most everyone had to agree. That’s all. And when you think about it, all the terms we use for measurement came to be in a similar way. What makes a meter a meter, or a gram a gram? How about a kilometer and a mile? The movement from English units to Metric units didn’t change anything other than the way most folks decide to measure things. Units of measurement are nothing more than nods of agreement, like time. My grandkids measure days as “sleeps.” They’ll ask their mothers how many more sleeps there are until Christmas. On a long car ride, they’ll ask how many shows away the destination is because they’re all being raised with iPads.

There is nothing sacred about the British thermal unit. If you choose to call it the Canadian thermal unit it will still heat your home.

Thomas Tredgold figured he could get away with naming his new unit of heat after his beloved country because the British had kicked the snot out of Napoleon in 1815, and their empire sprawled so far and wide that the sun never set on the Union Jack. People will be people.

The French people weren't buying it, though. And neither were the Germans, which is understandable. They went Metric.

So I hope this may inspire you to start a pseudo-scientific movement. All you have to do is make up a new name for something and gather a group of fellow believers around you. Find agreement and you, too, will be famous.

Hey, even the hockey puck used to be the ricket.

Be an Imangineer

Years ago, I wrote a book called Pumping Away. I ended it by trying to convince my reader to be an Imangineer. At the time, I had no idea that Disney was using that noun to describe their creative people. I just loved the sound of the word.

I encouraged my reader to think about the color and the weight and the texture of a British thermal unit and other things that we can’t see but we can feel. I wanted my reader to be able to do this because there will be days when he or she will have to explain this invisible thing to people who know nothing about heating, but who might buy something if the Imangineer can make the potential customer see what's going on.

Light a match, I said in my book. Let it burn unit it reaches the very tip of your finger. The customer will watch, sitting on the edge of her seat. "That's a single Btu," you will say. "When your burner comes on, it will be like 7,500 books of matches, all flaring up at the same instant. Imagine that power!"

Imagineers paint word pictures and people love word pictures.

A clever Imangineer might say, "A British thermal unit rides on the water like a passenger rides on a train. He gets on in your boiler and off in your radiators. I size the pipes properly so all the passengers can fit on the train." Your customer nods her head in understanding.

When a carton was magical

Think back to when you were a kid and the world was filled with wonder, when you saw creatures in clouds and the sky in a puddle. Think back and remember how fertile your imagination was in those days. Think about how a cardboard carton became so many things for you, even though it remained just a cardboard carton to the grown-ups. You showed them, though. didn’t you?

Strive to reclaim that part of your imagination. Bring it back to those days of wonder. Think about what a British thermal unit looks like. How big is it? How does it feel in your hands? How much does it weigh? What color is it? What does it smell like? Think, imagine, and wonder. And then go describe it to some little kid, and don’t stop describing it until she smiles in understanding.

When you can do that, you will be able to sell anything to anyone.

Ks and Ms

Speaking of making things up, how about those letters K and M that wind up in Btu ratings? I’ve seen those two confuse a lot of tradespeople. Here’s the story: The K in KBtu means 1,000, and it represents how many Btu you need per square foot of conditioned floor area.

But then we switch over to MBtu and MMBtu when we’re talking about natural gas. The M goes back to the Romans and their numerals. It means 1,000, not one million, but if you see two Ms used together (MMBtu), that means one million (a thousand thousand), even though, to the Romans, MM means two thousand.

Why do engineers do things this way?

Because they can.