Skip to Content

The Legacy of Gil Carlson, Hydronics Pioneer

Gil Carlson first pointed out the importance of a circulator's location in a closed hydronic system. In this episode, Dan Holohan shares how his teacher’s curiosity and brilliant mind changed the way we pipe heating systems.


Episode Transcript

Gil Carlson passed away on April 28, 1994. He was 72 years old and he was my teacher. At the time of his death he held seven U.S. patents and was recognized internationally as one of the foremost authorities on hydronic heating.

Bob Dilg and Gil Carlson worked together at Bell & Gossett during the early-Sixties. Bob said, "One night after work, I found Gil standing in the parking lot. He looked bewildered, so I asked if he was okay. He said, 'Yes, but someone has stolen my car.' I told him I would go back inside and call the police, but Gil said no, and asked if I could just take him home. Doris would have dinner waiting, and she would be worried if he were late. He would call the police from there.

"As we drove up to his house, I noticed Gil's car in the driveway. Gill saw it as well, and without any surprise whatsoever, said, 'Well, I suppose Doris must have driven me to work today.'"

I think Gil lived more in his mind than he did in the world. He churned constantly, always on his way toward places most of us couldn’t imagine. He saw things most of us missed.

He and I were sitting in an office in Manhattan one day when he told me a story about a problem job he had visited in 1953, and not far from where we were sitting. Hydronic heating was still wearing diapers in 1953. Gil was with Jack Hanley, who was Bell & Gossett's Eastern Field Representative back then.

It seems that the installer had used Monoflo tees on some perimeter radiation loops in this large office building. The problem, however, was that the pressure drop through each Monoflo circuit was much too high. The water refused to flow through the radiators. It stayed in the main. Water will do that to you. It’s lazy. And it loves the path of least resistance.

After a few calculations, Gil suggested that the contractor use small booster pumps on each circuit and run the main pump continuously. If the contractor wanted, he could cycle the booster pumps on and off with thermostats and that would give them zoning as well. Can you imagine the look on that long-gone contractor’s face? And that’s how primary/secondary pumping came to be.

Today, we use primary/secondary pumping all the time without giving it much thought, but isn’t it nice to know it all began with some creative thinking on a problem job in Manhattan? It began inside Gil Carlson’s mind.

Gil graduated from Purdue University as an engineer and went to work for Bell & Gossett in 1946. He retired from there as their Director of Technical Services in 1988. He also served on the Industry Advisory Committee of Purdue's Herrick Laboratories for 32 years.

In 1953, when I was three years old, Gil joined the American Society of Heating and Ventilating Engineers, which later became ASHRAE. Not long after joining, and in collaboration with B&G's chief engineer, Harold Lockhart, Gil presented a paper to ASHRAE. He called it, Compression Tank Selection for Hot Water Heating Systems.

At the time, the Lockhart/Carlson paper represented breakthrough thinking in the science of hydronic heating. It greatly simplified the compression tank selection process and saved countless hours of labor.

That first paper led to a second - the famous "Point of No Pressure Change" thesis, which proved that hydronic systems operate best when the circulator is on the supply side of the boiler, pumping away from the compression tank. I borrowed liberally from Gil's thesis when I wrote my book, Pumping Away in 1994. Nowadays, I sometimes get credited with original thinking because of that book. But the truth is, when it comes to hydronics, I haven't had an original idea in my life. It was all Gil. He gave me a way of seeing it all in my mind’s eye.

Bob Dilg once told me that Gil wanted him to go college because he had no degree. Gil wanted him to grow. Bob said, "He constantly encouraged me to further my education by taking night courses. When I told him that any degree would be years away, Gil just smiled and said, 'But you'll be smarter every day!'"

Gil would always take the time to share what his fine mind held. He could make a novice feel comfortable with even the more advanced systems because he had this wonderful ability to explain technical topics in a visual way. He didn’t deal in mumbo-jumbo, and he didn’t pick nits. He would always say, "A difference to be a difference has to make a difference." That stays with me because it applies to so many things in life, and not just hydronics. A difference, to be a difference, has to make a difference.

He also used to look at me and say, "Always remember that whatever goes into a tee, must come out of that tee." That’s what made me see the simple beauty of hydronics. It was all about pressure differential, or what he called Delta-P. Look to the tee and you will see the pure beauty of hydronics. Whatever goes into a tee must come out. But how? See it in your mind’s eye. That was how Gil taught.

Bob Dilg said, "He was singularly, seemingly unimpressed with his own genius. One time I went into his office and he was holding a dirty piece of cardboard. It was probably from the back of his favorite yellow sketchpad. He had cut it in a circle and he had drawn some marks on it with a pen. I asked him what it was and he told me he used it for calculations. He never could find the book or charts he wanted. In any event, what he had in his hand eventually became the Bell & Gossett System Syzer. He just never realized that piece of cardboard he had cut and marked-up might be of use to the rest of us."

Time went by and I came to be the caretaker of that round piece of cardboard that Gil had cut by hand. Gil gave it to his friend, Jim Hope, before retiring, and Jim gave it to me. I gave it to Robert Bean, and it is now the Carlson-Holohan Industry Award of Excellence, which, I think, would have pleased Gil. It certainly pleases me.

Once while on a problem job in Philadelphia, Gil took another piece of cardboard, this time it was the cardboard tube from a roll of toilet paper. He drew some marks on it and told the contractor to take him to the ball valves that served the radiators. He held the cardboard tube over the ball valve’s handle, and using a slide rule, calculated where the valve handle should be to provide the proper flow to that radiator. This led to his patent for what became the Bell & Gossett’s Circuit Setter. Gil saw the magic and the potential in ordinary objects of everyday use. Things like cardboard. Imagine that.

Bob Dilg said, "He was so prolific, that he would have these overlapping ideas. He couldn't keep up with his own mind. He once tried a Dictaphone, but that only made things worse since the secretary would type what he had said. The typed copy rarely made any sense. It was part of one thought, mixed with another, and smeared over a third and a fourth. He went back to using pen and paper.”

Bob also told me that ITT bought B&G during some rough recessionary years. They began to cut costs by reassigning some people and letting others go. These cuts troubled Gil because he always knew that there was so much to do. His mind just kept churning out one idea after another.

Bob told me there was one event that Gil never knew about. An ITT man saw Gil strolling the hallway in his fashion with that faraway look in his eyes that signaled he was deep in thought. The ITT man raised the question among others as to who this person was, what he did, and whether he was necessary on the payroll since 'he seemed to lack urgency.'

"This, of course, was completely true,” Bob said. “Gil never lived by his watch and sometimes had to be encouraged to go home. Thankfully, more knowledgeable heads prevailed and Gil's position was saved from the head-count reduction."

As time went by, Gil came up with improved procedures and charts for liquid viscosity pumping. He gave the hydronic-engineering community a new way to balance flow by trimming pump impellers. He wrote papers on air-handling and antifreeze design, as well as on flow-to-heat-transfer relations. He published more than 100 technical articles in Heating/Piping/Air-Conditioning magazine, and the ASHRAE Journal. That is the stuff I was raised on.

During the 1970s, he developed new ways to design solar-heating systems, cooling-tower systems, and variable-volume pumping systems. His fine mind ranged across a very broad field, but mostly he was a teacher. Over the years, he conducted hundreds of seminars, talks, and symposiums throughout the world. ASHRAE honored Gil with their Fellow Award, their Distinguished Service Award, and in 1986, the prestigious Life Member Award.

And he was my teacher. He taught me that whatever goes into a tee must come out of that tee. And I learned from that simple truth. And it made me see the simple beauty of how hydronics works. And when he passed from this life, I thought about how what goes into a life, must also come out of that life. So much came out of his, and I am forever grateful that he was born.

I hope you enjoyed this tale. And if you did, please share it with your friends. And please subscribe to this podcast. I have many more Dead Men Tales to share with you. Thanks for being here.

Leave a comment

Related Posts

The Legacy of the Dead Men

In this episode, Dan Holohan reflects on the Dead Men who came before us and the legacy they left behind. Episode Transcript My earliest memory of school goes like this: ...

Published on 12/27/2022 4:45 AM
Pivotal Advice

In this episode, Dan Holohan shares the advice that changed his life. Episode Transcript Advice sometimes comes unsolicited (like now) and other times it comes after you’...

Published on 12/20/2022 4:45 AM
Pipe Stories

In this episode, Dan Holohan shares the tale of how nominal pipe sizes came to be, as well as some comical work stories. Episode Transcript I called the plumber because t...

Published on 12/13/2022 4:45 AM