Noel Murdough
When you find yourself evaluating a residential steam system, it is good to have a systematic approach to go by. Sometimes, you'll be responding to a no heat call, sometimes you'll be evaluating a working system.
Of course, you'll need to begin with a code-required safety inspection of the equipment, which is a different subject, altogether. If the system is found to be safe to run, we can evaluate the steam side of the system.
We need to understand what type of steam system we are working with, to begin with. Start at the boiler, and try to determine which house piping is original and the same age as the rest of the house steam piping. This will be the basis for understanding what the system was intended to do. Follow the steam supply mains around the building and familiarize yourself with how the take-off tees are oriented, what sizes the tees are, how the mains get rid of the air in them, and how the mains handle the water that needs to return to the boiler. Determine which way the mains pitch and if they sag anyplace. Find any missing insulation on the piping, as it needs to be there to prevent excess water from forming in the mains and blocking the steam flow. Missing insulation is very common, but it prevents any balancing from being possible, and it drives up run times and fuel costs. It needs to be replaced with at least 1" wall pipe insulation rated for steam piping.
Look for any signs of steam or water leaks in the system, including vents that won't hold steam. Make the system steam tight. Fresh water is what kills steam boilers.
Look for any unusual devices in the steam piping that are different and unique to this system. Identify by brand and part number any devices that are original to the system. One pipe steam systems are usually pretty simple, it's the two pipe systems that have added check valves and cast iron recievers and venting controls. These devices were there to put the water back into the coal boiler if the pressure climbed above about a half pound. The pressure control on modern boilers keeps the pressure under a pound on these systems, so that the water can fall back into the boiler by itself. Often, the standard high limit pressuretrol on the boiler doesn't go low enough, and it requires a vaporstat in addition to the limit, to do the job. The boiler steam pressure is what determines the water level in the RETURNS, as the steam pressure pushes down on the boiler water and forces it up into the return piping. It rises toward the open vent 28 inches for every one PSI of steam pressure in the boiler.
You can observe the height of the water in the returns with a simple clear hose. Put a female hose fitting on about 15 feet of clear hose and connect it to the boiler drain. Open the valve and let the mud out of the hose till the water is liquid. Hold the open end of the hose above the boiler and piping high enough that the water doesn't run out. The water line in the hose should match the waterline in the boiler gauge glass if the burner isn't running. When you fire the burner, the pressure in the boiler will rise, and push down on the boiler water. The water in all of the boiler return piping and in our hose will begin to rise. It will all rise to the same level, determined by the boiler steam pressure (28" to the pound). If the water is pushed high enough to spill over into horizontal return piping, the boiler waterline will begin to fall. There is enough water in the boiler to fill the return main drop (and your clear hose), but as soon as the water finds a horizontal main to fill, the boiler waterline is in trouble. The next two inches of pressure increase will flood that entire main with water from the boiler. It could even trigger an automatic feed valve to feed, flooding the boiler at the next start-up. Control the steam pressure and you control the water level.
On the same subject, observe the water level through your hose to determine boiler pressure as it runs up it's range, and get an idea of where it runs to. Then run the pressure up to cut-out, and shut the switch off. The water in the hose and the returns should fall almost instantly with the steam collapsing as the radiators condense at their normal rate and the fire doesn't replace that steam. The returns will hold water back (at the height in the hose) if they are plugged, so if the hose drops fast to the boiler waterline, then both creep higher together when the return riser finally drains back, the returns are slow. If the returns are grossly plugged, water will have been stacking up out in the system, and the flooding after shutdown will be even greater. The hose will show this rise as well as the gauge glass, if you mark them as soon as your steam collapses, but before the water comes back. The water in the returns SHOULD fall down as fast as the water in the hose. If there is a delay, plan on changing the plugged returns.
This would be a good time to bring up boiler sizing. If the boiler is oversized, it will run up to pressure very quickly and shut of by the pressure control. It'll come right back on and repeat the cycle over and over again. On a closely sized steam system, the thermostat will normally satisfy before the pressure control opens for the first time in the cycle. When coming out of setback, the thermostat will normally call for steam long enough to satisfy the pressure control and cycle on and off by it. Unless you are changing the boiler, there isn't much you can do for an oversized steam boiler. If you ARE changing the boiler, find out how many square feet of radiation there is connected, and size the new boiler to that load.
Let's look at the venting next. On a two pipe system, the mains all vent into the returns and then out a main vent or a vent pipe on a condensate tank. The whole return main should never get to steam temperature. If it does, something has failed. More later on two pipers. On one pipe steam, it should take about two minutes from the time that the boiler header gets hot with steam till the main vent on the end of any steam main gets hot and closes. If it takes longer than about two minutes, the vent on that main needs to be bigger. The key to balancing a one piper is to get the steam to enter all of the radiators at the same time. If it takes four minutes to fill the mains, the first radiator will have four minutes of steam in it while the last radiator has four minutes of air in it. It's tough to balance a radiator that doesn't heat for four minutes, because the run cycle could be twice as long in cold weather as it is in milder weather. Which case do you balance for?
If they all begin to heat together, and they all cool together, then you can balance them against each other with individual radiator vents. The vents can be swapped from a fast radiator to a slow radiator, or you can buy new vents at the correct size, or some are even adjustable. Try to have the vents as open as possible, for the fastest heating and shortest run times. If you can hear an air vent venting, there isn't enough venting on the system. If you can hear them venting, the air is moving so fast that it picks up rust and dust and eventually plugs that vent. The other vents then have to handle more air; they speed up and plug, too. You shouldn't hear an air vent when it's working properly.
We've been around the system now, let's look at the boiler itself. See if the waterline is steady when running, and the water in the glass is fairly clean. If it's bouncing more than about a half inch, the water is dirty and or oily. It'll heat much more quickly, quietly, and economically with clean water. Follow the manufacturer's instructions for skimming the oil off the top of the water, and fill with clean boiler water when you are finished.
Look at the boiler piping diagram in the installation and operation manual. Make sure the boiler riser(s) are high enough and large enough. Make sure the header is built to the manual's specifications. Make sure that the last fitting on the header is the elbow that points down into the equalizer. Make sure that the equalizer isn't undersized. Measure the height of the Hartford Loop tee, and compare that to the manual. Be sure all of the instructions are followed to the letter. It might heat otherwise, but not as efficiently as it could.
If it is a two pipe system, the balancing is not as critical, in that any radiator valve in the system can be opened or closed at any time without affecting any of the other rooms. If there is steam getting into the return piping, the balance will be effected. The steam in the returns will close the traps that it reaches, which prevents any water or air from leaving the radiator side of that trap. It will stop heating.
There is a certain minimum amount of maintenance required on two pipe steam systems, weekly and periodically. Steam traps usually find themselves in the periodic category. Unfortunately, periods can be quite long, and viewed as an "all or nothing" venture. They get deferred frequently. There can be other alternatives to this, however.
There is nothing as easy as deciding to change every single trap and calling it cured, except not doing anything. Those are usually the two choices presented. The third choice is pretty labor intensive. It involves identifying exactly what is installed in the building, what is wrong with it, what it would take to fix it (broken down in stages), and what order to do it in, and what each stage would accomplish and cost.
This would chip expectations down to manageable and budgetable projects, and might give incentives to combine steps where it would save money to do so. It would help project for future budgets what the actual maintenance costs are on a large building with a seventy five year old heating system. It would maintain fuel consumption at predictable levels.
It would show how thrifty it is to keep up with steam trap maintenance. I'd like to help discover how to do this in layman’s terms. My experience is with four story brick residences with various vapor systems from 1910 through the 1960s. These were mostly two pipe vapor systems.
The very first thing to do is to identify the individual steps in an outline form that will bring the system back to working properly. Identify the system from trap names, unusual items in the returns or near the boiler, supply valve names, something to date the system with. This helps a little. Identify the height above the boiler water line to the lowest horizontal piping in the whole system that is above it. This is a "B" dimension, and is most important if there isn't a vented condensate tank or boiler feed tank. It defines what pressure the system was meant to be run at. Identify what vent is on the system and if it works, and at what rate it vents.
The first thing to address on the outline would be venting, as it has the biggest payback to cost ratio. Simply size the vent properly for the load and pipe lengths, and make sure it vents when it is cold, and it shuts when it gets hot. Make sure it is back from the end of the main about a foot or two, or more. It can even be right after the last radiator connects to the return main. There is likely to be a crossover pipe between the supply main and the return main there, with a radiator trap as the union and elbow on the return end. This is the supply main's air vent into the return. This flow is from supply to return to air vent. To keep the air and condensate all flowing the same way, the vent will be downstream and downhill from this crossover connection.
The next item on the outline will be to crank the pressure down to the pressure just above what it takes to get the main air vent to close. Identify that the control on the boiler might eventually need to be replaced with the one required to run this particular system at the design pressure. More on this later.
The next item to successfully tame the system is going to be insulation on all of the pipes. It simply must be in good shape to deliver all of the steam that they were designed to carry. If the steam condenses within the mains, the cross section of the pipe becomes reduced and the mains cannot carry the steam that they need to at reasonable velocities. The speed picks up and the water starts flying around, the noise goes up, the cost to run goes up, the vents and traps get hammered into little crumpled balls of metal inside. The insulation is mandatory. The mains are actually TWO pipe sizes too small, if the pipes are bare.
Along with insulating, the boiler piping must be right before the insulation gets applied. The first thing to do is to determine what the boiler needs to do, and if it will. We finally have come down to measuring the load connected to the boiler, and the size of the boiler, and to actually verify the firing rate and combustion efficiency. A filthy oil boiler that had been downfired beyond reason won't show up from a peek at the rating plate. It might make sense to look at the boiler size itself and it's piping, and start from scratch. It might be fine. Be sure the boiler piping matches the manufacturer's instructions, to the letter. Undersized piping might be the problem. Now is the time to decide.
If you have come this far, and have a working system to evaluate the steam traps with, you can move to the next step on the outline. You need a trap survey; a document that you make that shows what each trap model number is, and what room it is in. You need to group them by which branch of the RETURN main that they empty into. The return mains are groups of traps to be maintained and troubleshot as a group. It helps to begin thinking of them that way early. Along with this list of traps, a piping plan would be wonderful. These documents should be filed in a way that they outlast you on the job.
Once you have identified a return main, and have the steam pressure cranked down as low as it will go, start the system up cold and see if the return main becomes steam hot at the vent, up on this end of the return. Since only air is supposed to be there, and cooler condensate, it should remain open and not be steam hot. If it gets hot within minutes, you have a trap blowing steam through. On a system with working steam traps, and on ALL pumped condensate systems, the vent isn't needed. It only sees steam if a trap lets steam through. An open pipe could serve as the vent.
Take it out, if it isn't too much trouble, while you troubleshoot. It will speed up the whole process. The way that we are going to discuss checking traps isn't the only way, by any means. My focus is on cost of materials, but admittedly it is very labor intensive. This isn't developing a free estimate for repairs, this is actually a very valuable part of DOING the repairs, and should be thought of this way. The reason for the trap survey in advance is, in part, so that some repair parts for traps can be brought in and kept on hand. This enables repair as the testing evolves.
The premise of this method of testing is to follow the steam as it expands into cool piping in the supply mains, and detect, by external pipe temperature, where the traps let steam pass through. I started by using my hands, but years later, infrared thermometers with laser pointers came along, and they cut the time in half.
Start up the boiler until you detect steam in the returns someplace. Shut off the boiler and follow the hot pipe back to it's source. You'll get near it easily enough; close radiator valves off to eliminate their traps; identify how the steam is blowing into the return. Shut the boiler off often because once everything in that return main becomes hot, the information to be gained is very diluted. Keep everything cool, and squirt steam through by firing the boiler once in a while to keep the path hot. This is more art than science.
After the return main stays cool, because all of it's traps are fixed and holding, or shut off from steam, open up radiators one at a time with the steam on. As you open a radiator, check the return for live steam. Condensate dripping into the return will warm it up. Steam blowing into it will make it a blistering 200° F plus, right away. Shut those back off. Mark those for repair.
Here's another note. On a return that you know has steam blowing into it, shut the boiler off with hot mains, and let the vent pipe draw air in until it stops. With all of the radiators and valves open, start up the system again. As soon as the system vent pipe gets hot, go through the building and find HOT HOT traps on radiators that have COLD or cool sections right next to the radiator trap. This will tell you two things. One, there is obviously steam in that return. Two, THIS TRAP IS WORKING!!! It won't let the air from the radiator into the return, which has an open vent on the other end. It is keeping the radiator from venting. Write this one down on your trap survey as good. Look for more. Cool it down and start it again. Check again. Shut some off in a pattern that makes sense along the return, to determine where the steam is moving around. Some of the radiator valves won't hold steam all the way off, but that's OK. As long as the radiator condenses what it does get, and the last section doesn't get steam hot, you'll be OK. The room will use that heat, anyway. It's temporary. Leave off whatever it takes to keep the returns from having steam in them. For temporary heat, crack open radiator valves to allow half the radiator to get hot, but NOT THE TRAP!!!! Fix the crossover traps and the F&T traps on the mains. Get your vent to be cool while the system runs.
Now make a list of the traps on radiators that are shut off. These are what you need to replace. Leave the radiators with bad traps off in the meantime, or mostly off, to save the remainder of the working traps. Budget your replacement costs, but remember that more will fail as time passes. It will often be fewer than expected, though.
Now that the system is tame, and half shut off, the boiler waterline will be pretty wild, due to overfiring. Get the traps fixed to get the load back on the boiler, and troubleshoot from there. Have a very clean system with clean water. This is a whole different subject, but very important.
If the system floods after it runs, or if it runs out of water and shuts off, suspect plugged returns that are below the water line. Don't waste any time on them, replace them. Pipe them so that you can remove an air vent and flush them with a hose to a drain valve that you put in at the boiler end. Use mud legs to collect debris.
Once you get an intimate knowledge of the system, a loving pat on the air vent while it's running will tell you if you need to check your traps again. It should run at virtually the same temperature all of the time, a little hotter in very cold weather.
If you want real economy, buy a vaporstat that operates from 0-1 PSI, and is graduated in ounces. Install it at the boiler, or even better, at the end of the steam supply main. Wire it to break one leg of the thermostat wire through it, and leave the pressuretrol as is, as a high limit. Set the vaporstat as low as you can and still heat every radiator.
All of this would be done with the service person AND the weekly operator. The more involved with the system that the operator becomes, the more known and less costly will be the maintenance plan.
Along the way, you'll both learn the system. You'll find that return that's ALWAYS hot, no matter what. It'll drive you nuts, looking for the cause. Eventually, you'll find the crossover trap in the wall at the end of the main in the finished basement. It'll be behind a wall hung radiator.
You'll find the F&T trap that works, but it has a 3/4" bypass around it with a very painted plug cock in it; wide open.
You search the building and find two more. Guy's have been rebuilding these traps for 90 years, yet the bypasses never were closed. Originally, this system made heat and electricity by coal, the bypasses are from those days.
I want to close with a story. It is very relevant, and it was costly. It was a four-story residence, and the bottom floor was four feet in the ground. The returns ran around the bottom floor ceiling with the supplies, until they were pitched down to a point 30" above the floor, then the return split into a high and a low return back to the boiler room, the same on both ends of the building. The west end had steam in the front return, as a door on the ends of the building split the returns into a back and a front on each end of the building.
This front, west return had steam in it near the boiler end, the low end. The rooms all had thermostatic radiator valves on the radiator inlets, so each had control. The front door entry was always cool, and the radiator always hot. The next room had his thermostat off, because his room was hot enough, and the trap was hot and the radiator burbled steam into it through this hot trap. The radiator would fill with condensate until the system satisfied, when everything would cool off and drain back to the boiler. He opened and closed his window for temperature control.
The next room had the same hot trap and shut-off thermostat, but he was roasting. He NEVER closed the window. He went away every chance he got. One weekend when he was away, it was very cold. The whole weekend never saw above zero temperatures. The guy in the end room by the door called for no heat. Even with the valve open, no heat would come from the radiator. His walls were FREEZING. The hallway wall, the entryway wall, the outside wall, and the room next-door wall.
The radiator was full of water. No steam could get in. Draining it by shutting off the boiler got the radiator to heat but the room didn't heat well.
The wall to the next room was freezing. Uh - oh. In the maintenance guy went, to check on it. Everything was frozen. Bottles on the dresser had broken. The window was open. The radiator had exploded. He shut it off, shut the window, left the door open and went to call in some help. He was gone for a short while.
The frozen and split 1" sprinkler had thawed out while he was gone. The whole time he was gone, a 1" sprinkler pipe filled the west half of this building. About 11 people lived in the lower level, and they were displaced. The water was a few feet deep. Several people on the next level were also displaced to hotel rooms, until the building was renovated.
The steam traps were repaired right away. The rooms were comfortable, after that.