You probably see them as generic, throw-away items, right? A radiator vent is a radiator vent, and low price matters. Right?

It wasn’t always that way. There was a time when people dreamed about the radiator vents we use today. They dreamed because there’s never been a steam system that didn’t need to be vented, and in those days, there were no automatic air vents. Venting was a manual affair. You opened and closed a petcock on each radiator when you wanted heat. 

This bothered Moses P. Breckenridge, famous Dead Man. He rose to the challenge in 1868 by inventing a radiator vent that worked with a bimetal strip. The Breck, as the old-timers called it, stayed open to vent air. Then, as steam approached, the curved metal strip heated and expanded, closing the vent hole. Attached to that vent hole was a small pipe that connected to an ejector in the boiler room. The ejector used steam to produce a vacuum. This sucked the air from the radiator and sped heating. 

It was a simple device and better than a petcock because it made steam heat more automatic and people liked that. The Breck vent became one of the building blocks of the heating industry. Years later, Mr. 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, Conn., 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, just about anything that would expand when heated. Names such as Victor, Jenkins, and American appear in the old heating books.

The drawback with all these vents, though, 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 temperature. 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 vents really were.

Water 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, not need adjustment beyond the original factory setting, be able to withstand high temperatures, and be affordable.

In 1912, George D. Hoffman of Waterbury, Conn., finally met all the criteria by patenting his Number One radiator vent. The heart of this new air vent was a float that Hoffman had partially filled with a mixture of alcohol and water he had set to boil at about 180° F. 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 the radiator gave off its heat, the alcohol/water mixture inside the float also condensed. When the steam pressure inside the radiator dropped, the vent’s float fell, opening the vent port to allow venting on the next cycle.

The float would also close the vent port if water surged toward it under steam pressure. And any water trapped inside the vent could drain because this new vent had a siphon tube attached to its inlet tapping. It was simple and meant to last for years.

The Number One vent wasn’t affected by high temperatures and it was priced right. By 1921, Hoffman had sold more than 2 million Number Ones. 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 the vent.

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 1920s and 1930s. I still see some in service.

George D. Hoffman followed up with his Number Two radiator vent (a name I probably wouldn’t have chosen). This one had a tiny check valve at its vent port. He had vapor-vacuum systems in mind with the Number Two.

As a coal pile burns down inside a boiler the amount of heat available to turn water to steam lessens. But if the system is in a vacuum, the boiling point of the water will be lower, and that will cause more water to turn to steam, albeit at a lower temperature. Hoffman made this happen by adding that check valve. Air could leave the radiator but it couldn’t easily return, so the vacuum formed, making the most of the remaining coal.

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. 

Time passed and steam heating ruled for years. The trade began to look at radiator air vents as a commodity and the public began to fiddle with them when they didn’t have as much heat as they wanted. Vents get picked on because they’re so visible.

And that problem led to another sort of radiator air vent. This one showed up in the 1920s. They called it In-Air-Rid and it was the invention of Leslie M. Stadelhofer of Newark, N.J. The American Radiator Company sold them. These vents were invisible because they were inside the radiators. How’s that for a brilliant solution? Put it where people can’t touch it.

It looks like a hexed plug screwed into the top tapping on the radiator section furthest from the radiator supply valve. There’s a label on the plug that reads American Radiator Company In-Air-Rid. Often, someone has painted over that label, which makes it even easier for the vent to hide.

The vent has a float and a vent hole, just like an exposed air vent, but all of this is inside the radiator. The In-Air-Rid also has a spring loaded seat that seals 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-last radiator section, and then upward into the final section. This ensures that the radiator heats all the way across. It’s brilliant.

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 the painters. I’ve fixed many heating problems with a paperclip. I loved seeing the look on the building owner’s faces when I did that.

There was a long and lovely learning curve with steam air venting, and the automatic air vent did not come easily to the heating industry. They really deserve more appreciation than we give them nowadays.