Air Vents and American History

Published: March 1, 2022 - by Dan Holohan


The automatic air vent didn’t come easily to the heating industry. It took hard work and a lot of very inventive thinking. Hearing this story will help you sharpen your troubleshooting skills.


Episode Transcript

I’ll bet you consider the steam air vent a common, throw-away, commodity item. Be honest. You don’t give them much thought, do you? Oh, sure, you probably think about the price when you’re buying them. But when you’re installing them, I’ll bet you don’t give much thought to how they work.

Most folks don’t.

But it wasn’t always that way. No, there was once a time when the Dead Men dreamed about the “common” steam air vents you use today. They dreamed because there’s never been a steam system that didn’t need to be vented in some way. They dreamed because in the early days of heating there were no automatic air vents. None at all.

Back in the 1850s when the Dead Men men were installing Steven Gold’s simple one-pipe system, they vented the air through the roof!

They had no choice. There were no automatic air vents. Venting was strictly a manual affair. You opened and closed a petcock on each radiator when you wanted heat. If you left the petcocks open, steam went out the roof. And that’s pretty wasteful. America needed a good automatic steam air vent, and whoever came up with the first one would do very well indeed.

Moses P. Breckenridge knew this. He rose to the challenge in 1868. Mr. Breckenridge’s vent depended on the expansion of a curved metal strip to operate.

The “Breck” vent, as the Dead Men called it, stayed open to vent air. Then, as steam approached, the curved metal strip heated and expanded, closing a port on the left side of the vent. The small pipe on the right-hand side was an airline that connected to a Paul system. A vacuum-producing device near the boiler, most likely an ejector, pulled air from the pipes and radiators to speed steam distribution.

It was a simple device – a lot better than a petcock because it made steam heat more automatic and more appealing to the public. The “Breck” vent was one of the major building blocks of the heating industry. And it all started with a man’s idea.

Years later, Moses Breckenridge’s son, Lester, spoke of his father’s invention: “I had begun to take an interest in the heating industry in 1868 because I, a lad of ten, was seated at the edge of the kitchen table down in Meriden, Connecticut, watching my father whittling out the patterns of a core box and baking in the kitchen stove oven the cores for the “Breck” automatic air valve, patented in that year.”

It’s a nice image, isn’t it? A boy sits at the kitchen table and watches his father whittle a simple device that would change the way people lived.

Other air vents quickly followed the “Breck.” They all used some type of expansion material. Most used bi-metals. Others used composition rubber, carbon posts, or just about anything that would expand when heated. Names such as “Victor,” “Jenkins,” and “American” pop up in the old heating books.

The drawback with all these vents was that they had to be adjusted with a screwdriver from time to time. And if you didn’t get them just right, they’d spit. Some, particularly those with the carbon-posts, were also very susceptible to high temperatures. If you raised the boiler pressure – even for a short time – the carbon would buckle and the vent would fail. People began to wonder just how “automatic” these automatic vents were.

Condensate was also a big problem. An expansion device alone couldn’t stop it, but a float could, and some of the early vent manufacturers tried (with mixed results) to use a float along with the expansion device.

It was an enormous challenge considering the technology available at the time. The perfect steam vent would have to: Close against steam and water. Need no adjustment beyond the original factory setting. Be able to withstand high temperatures. And also be inexpensive.

That was a tall order. In fact, it wasn’t until 1912 when George D. Hoffman of Waterbury, Connecticut finally met all the criteria by patenting his “Number One.”

The heart of this new air vent was a float that Hoffman had partially filled with a mixture of alcohol and water. He “set” the alcohol/water mixture to boil at about 180 degrees F. Then he attached the float to a needle that could rise up and close the vent when the alcohol/water mixture flashed to vapor inside the sealed float.

As the steam condensed and cooled in the radiator, the alcohol/water mixture in the float condensed as well. Then, when the steam pressure inside the radiator dropped, the vent’s float also dropped to allow for more venting.

In addition, the float closed the vent port if water surged toward it under steam pressure. And any water trapped inside the vent could drain because this new vent also had a siphon tube attached to its inlet tapping.

The Number One vent wasn’t affected by high temperatures and it was priced right. It took the heating industry by storm. By 1921, Hoffman had sold more than two million Number One air vents.

Their performance was so good (the trade returned fewer than 2,000 during the first nine years) that Hoffman began to offer a five-year guarantee on their Number One.

And like the “Breck,” the Number One played a major role in the advance of one-pipe steam heating. It was an extremely popular air vent during the Twenties and Thirties. I still find them in service today – even after all these years.

Today’s air vents are very similar in principle to the old Number One. For instance, consider the Hoffman #40.

Like the Number One, it has a float that’s partially filled with a mixture of alcohol and water. Hoffman sets that mixture to flash into vapor at about 180 degrees. When it does, the bottom of the float pops down and closes the vent.

Should water get into the shell, the float rises to close the vent. The tongue (which took the place of the siphon as radiator-design technology moved from the column-type to the thin, water tube-type) drains off any condensate that accumulates inside the shell on the down cycle.

George D. Hoffman followed up with his Number Two, which had a check valve at its vent port. As the coal pile burned down, the amount of heat available to turn water to steam lessened. But if the system was in a vacuum, the boiling point of the water would be lower, and that would cause more of it to turn to steam, albeit at a lower temperature. Hoffman made this happen by adding that check valve. Air could leave the system, but it couldn’t easily return. So the vacuum formed.

During the 1930s, when the Dead Men began switching from coal to oil, they found that these vacuum-type radiator vents caused problems because the vacuum would form before most of the air was out of the system. That caused the air to quickly expand and slow the flow of the steam vapor. The solution was to remove the vacuum vent and replace it with a vent that couldn’t make vacuum.

There was another air vent that showed up in the 1920s. They called it In-Air-Rid and it was the invention of Leslie M. Stadelhofer of Newark, New Jersey. The American Radiator Company bought the rights and sold them. These vents were for one-pipe steam and they fit inside the radiator.

This was brilliant because it put the vent in a place where people couldn’t damage it, but there was more to it than just that. In-Air-Rid had a spring-loaded seat that sealed the last radiator section from the next-to-last section. When steam enters the radiator from the bottom, it rises to the top of the radiator because it’s lighter than air. Once at the top, the steam wants to move horizontally across the top of the radiator and toward the vent. Without that spring-loaded seat, the steam would close the vent before most of the radiator was hot. But with it, the steam has to take a detour downward through that next-to-the-last section, and then upward into the final section. This ensured that the one-pipe radiator would heat all the way across.

The vent hole in the In-Air-Rid is the dot in the i in the word Air. If that dot gets plugged, the radiator won’t heat because the air can’t get out, so we need to beware of painters. I’ve fixed many heating problems with a paperclip. All I had to do was poke the paint out of the hole. I loved seeing the look on the building owner’s face when I did that.

So as you can see, there was a learning curve with good air venting, and the automatic air vent didn’t come easily to the heating industry. It took a lot of hard work and a lot of very inventive thinking. We don’t give them much thought nowadays. We take them for granted. But now that you know how they came to be, I hope you’ll become a better troubleshooter.

I also hope you liked that tale. And if you did, please share it. And if you haven’t already, please subscribe to this podcast. I have many more Dead Men Tales to share with you. Thanks so much for taking the time to listen. I’m lost without you! Thanks.