Short answer: It sure does, but not in the way you may think.

Steam traps trap steam but that’s not all they do. They also pretend to be air vents whenever the system starts. And I say “pretend” because the traps usually aren’t venting the air from the system. They’re just passing it downstream to a real air vent that will toss it out. This is an important job because every steam system ever built is open to the atmosphere and filled with air on start-up. Steam is lighter than air and won’t mix with air, so for the steam to move, the air has to get out of its way. If the air can’t get out, the steam can’t get in, and that means cold radiators and unhappy people.

So the steam traps all smile as the air moves through them. If you look closely, you’ll see those smiles at the outlets of the two-pipe radiators, and near the ends of the steam mains. That’s where the traps do their work.

Once the steam shoves the air through the traps, the steam is free to give up all those latent-heat Btu it carried from the boiler to the cold metal of the radiators. The steam turns back into liquid water, which we call condensate, and then flows by gravity into the return lines and makes its way back to the boiler. It’s a simple system with very few moving parts.

The steam that travels through the steam mains gives up less heat because the mains are insulated (or at least they’re supposed to be insulated). Once the steam reaches the end of a main, a float-and-thermostatic trap holds out its hand to stop it and keep it out of the condensate-return piping. All these traps, on the radiators and near the ends of the steam mains, are acting like traffic cops. They’re also acting sort of like the balancing valves in a hot-water system. They only allow through what’s supposed to go through.

And as I said, there are very few moving parts in all of this. That’s one of the nice things about steam heat. The radiator traps contain a liquid-filled bellows thermostat that is normally open to allow the air to pass. When the steam arrives, its heat causes the liquid (usually alcohol) inside the thermostatic bellows to boil. The vapor pressure of the boiling alcohol makes the bellows expand. There’s a pin at the base of the bellows that then moves into the trap’s seat. That stops the steam from going any further. In the typical steam-heated building the bellows will open and close hundreds of thousands of times each heating season. That constant movement takes its toll over time. The thermostat will eventually fail, and usually in the open position. The simple reason for this is the open position is the one that causes the most mayhem. You know the “Mayhem” guy in those Allstate commercials? Yeah, it’s just like him.

A similar thing will happen to the float-and-thermostatic traps as the years roll by, but because the traps don’t all fail on the same day, we always seem to have this boil-the-frog situation. That’s the one where we put the frog in lukewarm water and then slowly raise the temperature in a way that the frog doesn’t notice. By the time he does notice, it’s lights out for the frog.

In the heating world, when the steam traps fail to open they let the steam move into the return lines. That’s not good because we size those return lines to handle air and water, but not steam. They’re much too small to accommodate steam. Pound for pound, steam takes up about 1,700 times the volume of liquid water. When the failed traps let the steam into the returns, the steam is going to cause some very memorable water hammer. It will also pressurize the return lines and that will slow (or stop) the air that’s trying to make its way to the air vents. The steam will probably also win the race to the air vents and shut them down on temperature. Now the air that fills the entire system on start-up is trapped between two points of pressure, and that means no heat for most of the radiators.

This is when some knucklehead shows up to raise the steam pressure, which only makes things worse.


What should you do?  

The right answer is to fix the steam traps, but that costs money. And in most big buildings, not everyone is complaining about not having enough heat. In fact, some people have too much heat. Those are the folks who open the windows and heat the neighborhood, and this is where we must segue from engineering to sociology.

The contractor has to convince a large group of people that it is in their best interest to hire him to repair the long-neglected steam traps. These people rarely think with a common brain. They each have their own needs and they are all selfish, so they all want to know how much this is going to cost them.

The contractor gives them a price and everyone starts to gag. They switch to the common brain and decide to put off this distasteful business until summer, a time when they don’t need heat and will be able to think more clearly.

But summer is hot, so their thoughts turn toward air-conditioning.

We wait another year.

Winter returns and now things are worse because Mother Nature doesn’t care about anyone’s budget. Management eventually realizes that the traps aren’t going to fix themselves, so they call the contractor again.

“What is our return on investment?” the chairman of the board asks the contractor.

The contractor considers this and says he’ll get back to them, and this is where it really gets interesting.

During the late 1970s, when Americans were reeling from spiking fuel prices, some industry experts who knew very little about steam heating speculated on how quickly steam-trap repair would pay back. They wrote articles about this in engineering journals. They used large buildings in cities such as New York for theoretical examples. They began by considering the size of the orifice in the typical thermostatic radiator trap.

They then imagined the steam pressure at the boiler to be 2-psig, which is normal for heating a large building. They calculated the amount of steam that would pass through that trap’s orifice during a winter’s day, and then they added all the losses through all the traps to come up with a total for an entire heating season. The numbers were impressive. So impressive, in fact, the payback period for repairing failed steam traps wasn’t years, or months or even days. It was hours. And as you can imagine, this revelation caused many people to fix their steam traps. It was a wonderful time for contractors. They did the work and then the folks in the buildings sat back and waited for the tremendous savings to arrive.

But they never did arrive.

Now the experts had some explaining to do. It was an interesting time to be in the steam business.

Do you see what the experts had missed?

When the steam zipped though the failed steam trap it wasn’t venting to atmosphere. It was entering the return lines and giving up its heat there.

The heat wasn’t lost to the building; it was still there, but in the wrong places. Many of the radiators remained cold because the system balance was screwed up by the roving steam in the returns and the too-high pressure to which the knucklehead had cranked the boiler. The experts were thinking about energy waste caused by orifices venting into the air. That’s not what happens in the real world. Sure, the repaired traps made the building better balanced, more comfortable and certainly quieter, but the folks weren’t seeing the enormous fuel savings the experts had promised from trap repair. The experts hadn’t thought this through.

We learned not to make those monetary promises as the 70s melted into the 80s and beyond, but there are still some experts who think they can give a firm number when it comes to ROI on steam-trap maintenance. I’m not one of them. I just tell folks to do the maintenance that will make the system work as it should. That’s the only thing that makes sense. Don’t make promises you can’t keep. You can make the system much better, sure, but don’t expect payback by this afternoon.

So does it pay to fix those steam traps?

Absolutely, but probably not in the way you thought.