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Dan Holohan Heating Help Newsletters

These are helpful letters you can recieve via e-mail from Dan Holohan's Dan's common sense approach to steam and hot water heating problems can help the apprentice and the master. Dan's web-site also offers books and other heating related item to educate you and your employees, check it out! These news letters are reprinted with permission from Dan Holohan Associates, Inc. 63 North Oakdale Avenue, Bethpage, NY 11714, phone 1-800-853-8882.


Your Most Frequently Asked Questions About Cast-Iron Radiators Answered! Questions regarding the often elegant, cast-iron behemoths we love so much are as perennial as water hammer and squirting air vents. So, I thought I'd put some straight answers together for you in one convenient place. Here goes. Q: Can I successfully cut down the size of an antique cast-iron radiator? A: Maybe. It all depends on how the long-gone manufacturer assembled the radiator. A cast-iron radiator goes together in sections, like a loaf of sliced bread. Each section attaches to the next with round metal fittings called nipples. Nipples looks like very short pieces of pipe, which may or may not have threads on them.

Threaded nipples are unusual in that one side has a left-hand thread, while the other side has a right-hand thread. As the manufacturer turned the nipple one way between the two sections, it pulled both sections tightly together. After a few years of normal use and corrosion, the threaded nipples and radiator sections became one, never to separate again. Because of this, threaded nipples aren't available anymore. If you're looking to reduce the size of one of these old beauties, you're out of luck. And then there are push nipples, which are still available. A push nipple is a smooth piece of pipe that's beveled. The bevel makes the push nipple wider in the middle than it is at either end. Rather than screw the radiator sections together, the manufacturers who used push nipples pushed one section into the other, taking advantage of the nipple's bevel to create a tight seal. If your radiator has a threaded rod running between its sections, rest assured it has push nipples. Now all you have to do is get the beast apart. Loosen and withdraw the threaded rod. Next, apply equal parts of patience, pry bar, and elbow grease. If you're careful and persistent you should be successful. Remove the offending section and reassemble the radiator. If the old push nipples don't look so hot, get new ones. And don't waste your time shopping around for these because there's only one place you can go: Oneida County Boiler Works (Phone: 315- 717-0423). Give Bob a call. He'll want you to send him a sample of the old nipple (no matter what condition it's in) and he'll he'll take good care of you. Bob regularly helps people all across the country, and he assures me that Oneida is the only company around that still supplies these fittings. "If people could get 'em any closer to home, they wouldn't be calling me!" he says. I believe him. Once you get the new push nipple in place, tighten the push rods, and pull the radiator sections back together. (Gosh, I make that sound so easy.) Q: What's the best way to disconnect, move, and reconnect radiators for, say, floor repairs? A: First, take care with those old pipes. Make sure you're using two wrenches when you're loosening the union connections. Assume the position, and then turn one wrench while holding back with the other. Don't take any shortcuts here because if you attack old pipes with a single wrench the torque you create can, and probably will, break the pipe.

A hand truck with a few strategically placed blocks of wood will help you move the old beast out of the way. And if you're planning to take that old radiator down a flight of stairs proceed cautiously, and with plenty of help because an antique radiator can weigh hundreds of pounds. Q: If I decide to move a cast-iron radiator, where should I reinstall it? A: Ideally, a cast-iron radiator should be under the window (that's where the greatest heat loss is), and it should be as wide as the window. Its top should never peek above the windowsill because this lessens the convective movement of air around the radiator. Speaking of which, for maximum convective efficiency, the radiator should be 2-1/2 inches away from the wall. It took the old-timers years to figure that out. Q: What's the difference between a steam and a hot water radiator? A: It's the way the radiator sections go together. They may be nippled together at both the top and bottom, or just at the bottom.

Older steam radiators have nipples across just the bottom portion of the sections. This is because steam is lighter than air. When the steam enters the bottom of a radiator (as it always will in a one-pipe steam radiator), it flows upward into the sections, displacing the air as it goes. Hot water radiators, on the other hand, have nipples across both the upper and lower portion of the radiator sections. Even though hot water rises, it doesn't move as quickly as steam. The double set of nipples encourages better circulation of the hot water across the entire radiator and leads to greater efficiency. Around 1905, when two-pipe steam became popular, contractors began to use hot-water radiators on steam systems. The old steam radiators with their single set of bottom nipples quickly faded and became obsolete. Q: What's the difference between a one-pipe and a two-pipe steam radiator? A: As the name implies, a one-pipe steam radiator has just one pipe connected to it, and that pipe is always at the bottom. Both steam and condensate (the water that forms when steam condenses) share this pipe. One-pipe steam systems can use either steam or hot water radiators, however.

Two-pipe steam systems usually have the steam entering through a pipe at the top of the radiator. The condensate leaves the radiator through a pipe at the bottom. Since the steam moves across the top of the radiator, and the condensate drips down along the radiator's inside passages, two-pipe radiators generally provide a more-even sense of warmth.

There will usually be a steam trap (which is an automatic, temperature-sensitive valve) at the point where the radiator and the condensate pipe come together. You should check these with a thermometer once a year. You've looking for at least a 10-degree drop in temperature across the trap. If the trap's not working, you can replace the internal parts. Any good plumbing supply house will be able to get the parts for you. A two-pipe steam system will almost always use hot water radiators. There is one notable exception, though, and it's called the two-pipe, air vent system. You'll know you have this one if you see two pipes, one on each side of the radiator (at the bottom), and both pipes have hand valves. These radiators also have air vents. From a historical perspective, the two-pipe, air vent system is the missing link between one-pipe steam and two-pipe steam. Q: Does a two-pipe steam radiator have to have a steam trap? A: No, but it has to have something to keep the steam from entering the condensate return lines. That "something" may be an internal orifice, a tiny check valve you can't see, a hidden metal ball or a water seal. There were about three dozen companies doing business between 1905 and 1930 that made these steam-stopping gizmos. They're all out of business now. So do not remove any weird-looking device until you've answered three essential questions: What is it? What does it do? What the heck happens if I take it out? If you can't answer those questions, put your hands in your pockets, and back slowly away from that radiator.

Q: Can I take out a steam radiator and put in a hot water radiator? A: Yes. Q: Can I take out a hot water radiator and put in a steam radiator? A: You can if it's a one-pipe steam system. Q: Where does the air vent belong on a cast-iron steam radiator? How about on a hot water radiator? A: If it's a one-pipe steam radiator, the vent belongs on the side of the radiator that's opposite the pipe. Because the lighter-than-air steam will head first for the top of the radiator, you should install the air vent about half-way down the radiator, and not at the top.

Two-pipe steam systems (with the exception of that "missing link" one-pipe, air-vent system) should not have air vents on the radiators. If the two-pipe radiator won't heat without an air vent, check the steam trap. Misapplied radiator air vents can lead to nightmarish system problems. Each hot water radiator should have an air vent at the top, on the side opposite the inlet pipe. You'll use this vent to "bleed" air from the radiator when you're first starting the system. Q: Where can I buy antique radiators? A: You can take pot luck at your local junk yard, or you can call Fran Fahey at A-1 New and Used Plumbing & Heating Supplies, 30 Prospect St., Somerville, MA (Phone: 617- 625-6140). Fran operates a veritable supermarket of antique radiators in all shapes, styles and sizes, and all A-1 radiators, he assures me, are in A-1 shape. Fran told me he has repaired and pressure-tested every one of them. He'll ship anywhere in the country, and he'll also fix your old radiator or remove a section (providing it has push - not threaded - nipples).

Q: Can I repair a leaking cast-iron radiator? A: It depends on where the leak is and how bad it's leaking. Steam radiators, because they're under much less pressure than hot water radiators are usually the easier of the two varieties to fix.

To begin, first determine where the leak is. This, of course, is easier said than done. Go to your local hardware store and get yourself an inspection mirror, which will allow you to see around corners and up into spaces not viewed within the past 100 years. If you find a pinhole leak at a push nipple, you can, as you now know, replace the push nipple. If the radiator is cracked, say, after a hard-freeze, you may not be able to repair it at all, however. It all depends on the severity of the crack, and where it is. Q: Are there stop-leak products for cast-iron radiators (as there are for automotive radiators?) A: None that you can pour into the radiator, but J-B Weld Company of Sulphur Springs, TX (903-885-7696) may have the answer. The company's literature states that the City of Dallas, Texas used J-B Weld to repair a cracked Caterpillar engine block. That sure got my attention! A representative of the company told me that old-house owners have reported great success with his company's product, J-B Weld on old cast-iron radiators. But to fix a leak, you first have to be able to get at it, right? So consider this. Before using J-B Weld, you have to drain the radiator and remove any paint, primer, or rust. Next, you have to thoroughly clean the surface with a non-petroleum-based cleaner such as acetone or lacquer thinner, removing all dirt, grease and oil. Then you have to rough up the surface with a file, mix the two elements of the product in 50/50 proportions, and apply it to a thickness of no less than 1/32-inch. Don't get any on your skin or in your eyes. Finally, you let it dry for at least 15 hours, and see what you've got. Can you do that? I asked if the product could take the temperature along with the expansion and contraction common in cast-iron radiators. They told me the product actually "softens" when heated and will move with the metal. It's not the sort of 'softening' you'll notice, though. You'd have to get the temperature up to 400 degrees Fahrenheit, to see that (the product is good up to 600 degrees.) Typically, a radiator in a steam-heating system will get up to about 229 degrees tops. So if you can get at the leak, it sounds like this stuff will work.

The challenge, of course, is that an antique radiator can have more nooks and crannies than a Thomas' English muffin, and a good leak knows where to hide. But if you're in love with that old radiator, it's certainly worth a try. The company sells only to wholesalers, and only in quantity, but you can buy J-B Weld for about five bucks at most automotive and hardware retail stores. Q: Do I need to flush my radiators from time to time? A: No. Hot water radiators operate within a "closed" system where there's little or no corrosion taking place. Flushing these radiators will only cause you to add more water to the system, which will create more corrosion, and so on, and on. Why cause problems? Steam systems are open to the atmosphere so the radiators do see more corrosion than their hot water brethren. However, cast-iron radiators come with their own dirt-storage compartments, and these can hold many years' worth of scale and rust. Take a look at the way your radiators connect to your pipes. Notice how the inlet valve or outlet steam-stopping device is always a bit higher than the bottom of the radiator? This is true even when the valve is installed near the bottom of the radiator. The scale and rust settle into that low-slung "pocket" and stays there. Keep this in mind if you decide to pitch your one-pipe steam radiators back toward their inlet valves to give you better condensate drainage. Take care not to pitch those old beauties too much. If you do, you just might slosh one-hundred-year's worth of sludge into that inlet valve. You'll know you made this mistake by the water hammer that pounds on your pipes and the condensate that squirts from your air vents onto your ceiling.

That's when it's time to flush the radiator. Want more information? Visit us at


Steam pipes need insulation Think about this for a minute. Steam is a gas that desperately wants to give up its latent heat energy and turn back into water. It will give up that energy to anything that's colder than it is. In most houses, the steam will be 215 degrees. That's hotter than just about everything else, right? So when the steam hits a cold pipe, it will make that pipe hot by condensing on it. And when the steam condenses, it stops moving. The colder the pipes are, the faster the steam will condense, and that's why the Dead Men covered their pipes with asbestos "blankets." Asbestos insulation keeps steam from condensing. The Dead Men wanted to keep the steam warm so it would travel further like to those upstairs bedrooms. No one really needs a basement that's 85 degrees.

When you remove the insulation, it gives you the same effect as having an undersized boiler. The rooms heat unevenly. Some rooms never get hot. The fuel bills are high because the burner runs longer than it should if the thermostat's in a room with a cold radiator. You're also liable to get water hammer, especially if the asbestos abatement people didn't do a good job of reattaching the pipe hanger. Insulation makes a huge difference to steam mains. Here, suppose you had a 2-1/2" steel main that was 50 feet long. Let's say some Dead Man covered that main with a one-inch-thick layer of asbestos insulation years before you were born. When the air in the basement is 70 degrees, the heat loss of that main is going to be about 2,450 BTUH. Naturally, if the air in the basement is colder, the heat loss will be greater, but let's say the air is 70 degrees, just for the sake of comparison. Now, take the insulation off that pipe and watch what happens. The heat loss of the pipe jumps to an incredible 13,250 BTUH! That's more than five times the heat loss, and if the basement is colder (or if the main runs through a cold crawl space), the heat loss will be even more extreme. And that's why the basement is so cozy while people are freezing in the bedrooms. The load that the uninsulated pipe adds to the system can effectively undersize an existing boiler. When you size a steam boiler, you have to make sure its ability to produce steam matches the system's ability to condense steam. It's like having an evaporator and a condenser. The boiler becomes the evaporator, and the system becomes the condenser. If the condenser is bigger than the evaporator, the boiler will run for a long, long time before it shuts off because it will never be able to shut off on pressure. This will be most apparent during the spring and the fall because the boiler has to overcome the heat loss of the bare pipe every time it starts. During the winter months, when the boiler runs for a longer time, the pipes won't have as much of an opportunity to cool off, so the problem won't be as noticeable. Spring and fall will drive you nuts. The piping heat loss is what boiler manufacturers call the "pick-up" factor. When they rate their boilers they allow for a piping pick-up load that's equal to one-third of the system's radiation load. In other words, they figure how much radiation you'll need to heat the house, and then they add a third more boiler capacity to that to allow for the heat loss of the pipes that connect the boiler to the radiators. And they base this one-third pick-up factor on insulated pipe because you're supposed to insulate all steam pipes. When the insulation's gone, the pick-up factor the boiler manufacturer built into the sizing chart will suddenly be too small. And it's not just the steam mains that you have to consider. You should also insulate the return lines, but for a different reason. Return lines carry air and condensate, but not steam (unless the traps fail), so there's no chance the steam is going to condense in the returns. The reason for insulating these pipes is to keep the condensate as warm as possible while it's on its way back to the boiler. You see, as water cools it will absorb any gases it can find. When you boil water, carbon dioxide will leave the boiler along with the steam. This is natural because feed water contains carbonates and bicarbonates. When the carbon dioxide mixes with the condensate in the returns you wind up with carbonic acid. That's what eats through those wet return lines and makes them leak. By keeping the condensate as warm as possible, you lessen its ability to absorb carbon dioxide. Hot water simply can't absorb as much gas as cool water. Keep the returns hot and less carbonic acid will form. Your return lines will last much longer. Steam risers often run from floor to floor on the inside of the rooms. In some cases, the riser is the radiator. Many apartment buildings have risers running through bathrooms and kitchens where there's no room for a radiator. You can figure the output of these risers by using these guidelines: A 1-1/4" riser will put out .63 square feet EDR per linear foot A 1-1/2" riser will put out .73 square feet EDR per linear foot A 2" riser will put out .88 square feet EDR per linear foot So, for example, if you have an eight-foot-high, two-inch bare riser in a bathroom, it will put out about 1,690 BTUH (8 linear feet .88 Sq. ft EDR/linear ft. 240 BTUH/Sq. ft. EDR = 1,689.6 BTUH). When you're measuring your radiation, you'll figure this into your radiation load. The piping pick-up factor gets added to this, of course. In this case, the pick-up factor will actually be a bit more than normal since it doesn't have to account for those risers, which are actually radiators. If the risers are inside the walls, however, you won't be counting them as radiation. The piping pick-up factor will account for them in this case, but remember, the pick-up factor boiler manufacturers use nowadays allows for an addition that's equal to one-third of the total radiation load, and it assumes the pipes are insulated. If those risers are buried in the walls and they're not insulated, the pick-up load may be greater than anyone expected. You'll have to account for this when you're sizing the boiler by substituting the manufacturer's "built-in" pick-up factor for one that's closer to one-half the total radiation load. In other words, instead of using the standard 1.33 pick-up factor, you'll use 1.5 and then select the boiler based on the manufacturer's "Heating Capacity" column in their rating chart. How do you know whether those inside-the-wall risers are insulated. You don't. Assume the worst, and keep in mind that if you install a setback thermostat on one of these jobs, those buried, uninsulated risers will condense steam even faster because they'll go cold more often. The Dead Men who buried those risers figured they were going to be hot all winter long. Those guys burned coal, and coal stays on all day long, right? So insulate all the pipes you can see (unless you need them as radiators), and suspect the ones you can't see. And keep in mind that your insulation doesn't have to be fancy to be effective. You can use plain batt insulation and duct tape if aesthetics aren't important. Just keep the pipes warm so the steam has a chance to get to where the people are. Steam should condense in radiators, not in the basement. Like to learn more about steam heat? Visit the Books & More section at Lots of good stuff there!


The more steam heating systems I look at, the more I realize that nearly all the problems can be boiled down (couldn't help myself there!) to these four areas. When you're looking for solutions, look here: Air: The thing about air is that it's just about everywhere, which is good for people, but bad for steam systems. When you first start that steam system the pipes will be filled with air and air does a fine job of blocking the steam from getting to where you want it to go. And since you can't see air, you probably won't be thinking about it. Steam and air are both gases, but they have different densities. Steam is lighter than air so the two won't mix. This is why the Dead Men invented the air vent. The air vent's job is to vent air. How about that! The vent belongs downstream of whatever it is you're trying to heat - be it a radiator, a kettle, a heat exchanger, an air-handling coil, or whatever. The steam has to be able to push the air through the heater and out of the system. The vent doesn't belong before the thing you're heating. It belongs after. Got it? Good! When I'm troubleshooting steam, I always look for this first. Air will always be my Number One suspect. I walk the piping and ask myself this key question: If I were air, could I get out? And if I don't see a way out, neither will the air. If the air can't get out, the steam can't get in. It's as simple as that. The usual result is a cold heater. The usual reaction to this, unfortunately, is to raise the system pressure. Now, that's about the dumbest thing you can do because you can move more steam with a pinhole at the end of the pipe than you can with a ton of pressure back at the boiler. Try it once and you'll see what I mean. Vent the air from a point beyond the heater and most of your troubles will vanish. But try forcing the steam down a line that's filled with air and your troubles will multiply. The higher steam pressure will just compress the air. It will also hold condensate up in the system, increase the fuel bills, create water hammer, slam one-pipe steam air vents closed and never allow them to open again. Think like air! Give it a way out because that's where it wants to go. And make sure the way out is downstream of whatever it is you're trying to heat. Get out of the boiler room. Take a walk around and keep your eyes open. If you were air could you get out? Dirt: All steam systems are open to the atmosphere. They breathe air in and out. Steam condenses all over the place and wets the insides of the steel pipes. Put steel, air and water together and you'll get rust. That's where most of the dirt comes from. You have all these little flecks of rust that form on the insides of the pipes. The steam comes roaring along at a pretty good clip and rips those flecks off their perch. The condensate then carries the rust to the bottom of the system or the bottom of the heaters and there it stays, waiting to cause problems for you as time goes by. Once it gets where it's going, the rust combines with whatever scale has dropped out of the water to form a sludge that looks like a primeval ooze left over from the birth of the Universe. If you get this stuff on your hands it's about as easy to remove as a tattoo. Needless to say, it will interfere with the operation of your system clog up your air vents, return lines, calendar, mental process, etc. Add to this evil slime the oil that's in the boiler when you first get it and life gets even more interesting. Boiler manufacturers have to thread the holes they cast in the iron. They use these BIG drills to do that. There's oil flowing all over the place and when that oil gets into the boiler you have to get rid of it if you're ever going to make decent steam. And this is why boiler manufacturers print cleaning instructions for all the boilers that they sell. If you read those instructions you'll learn how to clean the boiler and the system and avoid most of the problems that plague those who are in too much of a hurry. Next, look right at that gauge glass. Look at that part of the glass right above the water. That part should look bone dry. If you see droplets of water (or a stream of water flowing over the top!) know that this is not normal. It is, however, your clue that the boiler and the system need a good cleaning. Read the instructions so you'll know what to do. And be prepared to clean the system about seven or eight times if that's what it takes. And sometimes, that's what it takes! Piping: Back in the old days, steam boilers were a lot bigger than they are nowadays. That's what made them steam boilers. They had wide sections so that the little steam bubbles could rise up through the water, expanding as they went, without causing a lot of surging when they broke free from the surface. Those old boilers also had large exit holes so the steam could leave the boiler relatively slowly. That kept the water in the boiler from leaving the boiler with the steam. Old steam boilers also had cavernous steam-disengaging spaces so the water would stay in the boiler as the steam headed out toward the system. Big as good. But modern boilers are much smaller so they can't provide all that internal space that makes a steam boiler a steam boiler. Boiler manufacturers do their best to compensate for this by providing specifications for the near-boiler piping. If you want to fail miserably, all you have to do is ignore these piping specifications. The water will leave the boiler with the steam, giving you water hammer, uneven heating, high fuel bills and a boiler that either goes off on low water or floods (if you have an automatic water feeder). If you follow the instructions, however, you will do very well. Your choice. The piping out there in the steam system is something else you should respect. If you don't know what you're looking at put your hands in your pockets and go to lunch. I don't have the space here to go into all the subtleties of steam system piping but just know that the size, angle and pitch of every single pipe you gaze upon is crucial to your success. If you want to be smarter than most in this area, read my book, The Lost Art of Steam Heating. You'll find it in the Books & More section at Controls: The good news is there aren't that many controls in a steam heating system. You have a thermostat somewhere up there in the space you're heating. You have a pressuretrol on the boiler. It's there to make the air vents work. You also have a low-water cutoff to keep the boiler from ending up in the next county, and finally, you might have an automatic water feeder, which is a back-up safety device for the low-water cutoff - NOT a convenience item. Maybe you also have an aquastat if there's a tankless coil for domestic hot water, but that doesn't have much to do with making steam. And if it's a really big building, you might have some sort of central controller that senses the outdoor air temperature and turns the boiler on and off. That's it. Now for the bad news: It is very, very easy to mess up any of these controls. If the thermostat's in the wrong place the temperature won't be right (obviously, eh?). If the pressuretrol's not set properly, the vents can get slammed shut (one-pipe steam) or the rooms will overheat (two-pipe steam). Always crank that pressuretrol down to the lowest setting that will still heat the place. I've never met a pressuretrol that I couldn't crank down. Unfortunately the urge to crank it up is often irresistible. Don't give it to it. Finally, if you have one of those central controllers, there's going to be a sensor that tells the system when to start and stop. This is the controller's brain but where that sensor winds up is entirely up to the whim of the person who first installed it and the contents of this second brain may be questionable. The sensor is supposed to be on a steam line, far out on the building, but I've seen them wind up on cold water lines, sewage lines, gas lines and plumbing lines. Why do people put them there? Because they can. Need more HeatingHelp? Visit us at and bring your questions to the Wall.


Some Tips on converting from steam to hot water Before the 1920s, most steam contractors used cast-iron, column-type radiators. Those are the free-standing ones with the real wide sections. Column radiators were perfect for steam heating because they had a lot of internal space and they allowed the steam to rise up and displace the heavier air. In the case of one-pipe steam, the air worked its way out of the radiator air vent. With two-pipe, the air escaped through the steam trap (or that old Vapor gizmo) and left the system through a vent somewhere down the main. Having a radiator with lots of internal space also allowed room for the condensate to get out of the way of the steam. The trouble with those old column radiators, though, is that their makers never intended for them to be used with hot water. Those individual radiator sections aren't connected across the top, and that presents a challenge with water. You have to look real close to notice this on those old radiators, and it's the very first thing you should look for when you're considering a conversion from steam to hot water. If you don't see those top push nipples, the conversion isn't going to be very easy - or practical. Water won't flow well through a sectional radiator that's not connected across the top. To make it work, you'd have to drill and tap each section and install air vents all the way across the top. Or, if you have a LOT of patience, you can wait for the system water to absorb the air and move it to the air separator. This could take months. After the 1920s, steamfitters began using cast-iron, tube-type radiators (the ones with the thin sections). These were actually hot water radiators, but they also worked well on steam systems. Building owners preferred them because they were nicer to look at. Tube-type radiators do have push nipples across the top of the sections, so if that's what you have, you can move on to the next step. And that next step is to check to see if your system is one-pipe steam or two-pipe steam. This may seem like an easy thing to do, but don't go by just one or two radiators. Many systems have a combination of both one- and two-pipe radiators, and that's perfectly normal - for steam. Look it over. While it's possible to convert a one-pipe radiator to hot water, it's sometimes not practical. You have to run a second pipe from the top of each radiator back to the boiler. Some folks use radiant-floor tubing to do this. They drill and tap the top of the radiator section that's opposite the supply valve and then run either PEX tubing or rubber hose back to the boiler, connecting it to the mains with cable ties as they go. Once back in the boiler room, they use manifolds with individual circuit-balancing valves to make their return connection to the boiler. Most plumbing & heating supply houses sell this gear nowadays. A conversion from two-pipe steam to hot water is usually easier to do, but examine the system carefully before you make a decision. Many of the older two-pipe systems were Vapor systems. There may be orifices in either the supply valves or the return elbows. Those radiator return elbows may also have tiny check valves or stainless-steel balls that can mess up the flow if you don't know they're there. Look the job over carefully and if you have any doubts, go to the Wall at and ask us. We do our best to help you. Before you break out the tools, do a complete and accurate heat loss calculation on the entire building. Don't settle for one of those cockamamie rules of thumb that has you measuring the cube of the building and multiplying by an arbitrary number. Rule-of-thumb methods will oversize your system by a ridiculous amount. Take the time to do it right. If you don't know how to do a heat-loss calculation, check out the Quick Sizing Forms available from The Hydronics Institute ( Once you get an accurate heat loss calculation, measure the existing radiation for square footage of Equivalent Direct Radiation (EDR). You're trying to find out if the radiation that's already in the building will be able to heat the place once the relatively cooler hot water is flowing through it. Keep in mind that one-psi steam in a radiator will bring the surface of that radiator up to 215 degrees. Hot water, by comparison, is usually only about 180 degrees, tops. A square foot of steam EDR will put out 240 Btuh. Convert that radiator to hot water and you're only going to get about 150 Btuh out of that same square foot of radiation. So, for instance, if you have a five-tube, 26" high, 10-section, cast-iron radiator running on steam, it will emit 8,400 Btuh. Convert the system to 180- degree hot water and you'll get only 5,250 Btuh out of that radiator. If you're looking for a fast way to figure out how much EDR is in a radiator, get a copy of my book, The Golden Rules of Hydronic Heating, which you'll find in the Books & More section at Once you've gone through that exercise, ask yourself if this lesser output from the radiators will be enough to heat each room on the coldest day of the year. This depends on the heat loss, and that's why you have to take the time to do both an accurate heat loss calculation AND a survey of the existing radiation. If, after you've done your homework, you find the existing radiation can carry the heat loss on the coldest day of the year, you can move on to the next step. Check the system for leaks. Keep in mind a steam system is used to seeing only about two-psi steam pressure. If there are leaks anywhere, you might not have noticed them at such a low pressure. This is especially true if the leaks are in the return lines. But when you fill the system with water the static pressure is going to be a lot higher. You'll notice those leaks for sure! It's so much better to find them before the conversion, if you can. A two-story hot water system will have at least 12-psi static pressure on it. A three-story building will have 18-psi pressure, and so on. Add in the pump's pressure along with the pressure of the expanding water as it heats and you can see the dramatic difference between steam and hot water. So before you commit to the job, raise the steam pressure to about 10-psi pressure and walk through the entire system looking for leaks. If they're there, they should show up under the increased steam pressure. Once you see them, you'll have a better idea of what you're up against, and you'll be able to make the decision as to whether or not you should move on from here. Next, if the system looks sound, you can take out the tools and go to work. You'll have to remove the innards from all the thermostatic radiator traps and float & thermostatic traps near the ends of the main (if you have them) so the water will be able to flow freely. Again, be especially aware of any old Vapor equipment. There's a big difference in size between the supply and return lines in a steam system so balancing will always be a challenge when you're running on hot water. Leave the old radiator supply valves in place if they're working. You'll be able to use them for balancing the flow and the heat once you have the system up and running. Most two-pipe steam systems are similar to two-pipe, direct-return hot water systems. The big difference is that, unlike a hot water system, the return line doesn't increase much in size as it returns to the boiler. With steam, the lines are picking up condensate, not the much greater flow of water you expect to see in a hot water system. Because of this, you may have to redo the return lines to accommodate the greater flow you'll be seeing once you've converted the system. Are you beginning to see why I prefer to fix old steam systems rather than convert them to hot water? The good news, however, is that each two-pipe radiator will have a return that's at least 1/2" in size. A 1/2" line can safely carry 1-1/2 gpm of hot water and that translates to about 15,000 BTUH, which is usually more than the typical radiator will need to put out to heat the average room. If you're going to keep the old boiler, you'll have to change the trim, getting rid of the gauge glass, the low-water cutoff, pressuretrol and near-boiler piping. If you're replacing the boiler, you'll still be getting rid of the existing near-boiler piping and setting the boiler up as you normally would with a hot water system. If you're not sure how to do this, get a copy of Pumping Away, which is also in the Books & More section of Size your circulator based on your heat loss calculation, not on the existing radiation. Take your gross BTUH load and divide by 10,000 to get the GPM for the pump. To figure pump head, measure the longest piping run, from the boiler to the furthest radiator and back. Allow six feet of pump head for each 100 feet of piping in that longest run. That's a rule of thumb, but it works well. Use a good air separator. Every hot water system needs a good air separator. Sizing the compression tank is tricky because there's going to be so much more water in those old steam pipes than you'd expect to find in a hot water system of the same BTUH rating. This is important because you base the size of the compression tank on the system's total water volume. Figure out how much water you have in the system, and then talk with the folks who sell the compression tanks. Don't depend on their quick-sizing charts in this case. They base those charts on standard hot water systems, not steam conversions. You'll have to get a count on how many feet of each size pipe you have in the system to estimate the total water volume. Here's a chart that will help you figure out how much water you can expect to find in each foot of pipe: Pipe Size Gallons in each linear foot

1/2" .016 3/4" .028 1" .045 1-1/4" .078 1-1/2" .106 2" .17 2-1/2" .25 3" .38 4" .66 5" 1.04 6" 1.5 If you've gotten this far, the next question will be, How do I control this hybrid I just created? The best way I know is to run the system on continuous circulator with an outdoor-air reset controller. It costs a bit more to set it up this way, but it is by far the best way I know to operate any hot water system, be it old or new. When you're finished and everything seems to be working well, graciously accept all compliments on your piping skills, engineering abilities - and general good luck!

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