I (Dave Yates) started working for F.W. Behler, Inc. as an apprentice in 1972 and later bought the company. After 49 years in the trade, I sold the company to a trusted employee and his family, Scott and Ryan Barnett. Later in my career, I founded a consulting firm (www.counsultyates.com), through which I serve as an expert witness regarding PHVAC issues and a hydronic system design and troubleshoot consultant.
Over the years, I’ve probably worked on 100 jobs that involved converting steam radiators to hot water. There was a time when we kept upwards of 80 used cast iron radiators in the shop for just this purpose.
Converting radiators from steam to hot water can be fantastic; comfortable, controllable and efficient. But there can be serious, costly problems if the work isn’t done correctly.
As a result of improper techniques or materials, we’ve been called to homes to find systems that don’t heat, over-heat, under-heat, heat unevenly, leak and make noise.
Due diligence
In the early 1900’s – and especially after the 1918 Flu Epidemic – people were under the impression that sickness was a product of having too little fresh air inside the home throughout the winter. As a result, systems were sized to accommodate partially-open windows. Science has moved past that notion, and we’ve moved beyond grossly oversized hydronic systems.
To actually convert a working, upper/lower-tubed radiator from steam to hot water and make it heat properly isn’t that difficult, if you’ve done your homework on the front end. By that, I mean completing a room-by-room Manual J load calculation to find the actual BTU requirements of the room at design conditions.
The next step is to complete a connected load survey (often called an Equivalence of direct radiation calculation, or EDR) in each room. Once both the EDR and BTU requirements are know, you can then consult the Hot Water EDR chart in your handy Burnham Heating Helper (Page 38). This will give you the correct supply water temperature required on a design-day.
Now you know what supply water temperature you need. One great thing about cast iron radiators is that – unlike fin-tube baseboard, where you keep supply water above 110°F to maintain convection current – you can let cast radiators drop as low as 75°F.
There’s great potential to save energy by maintaining lower water temperatures, especially if the system includes a modulating boiler. This grants full benefit of the
outdoor reset curve, so that the boiler never needs to supply peak (design) supply temperature unless needed.
If the home isn’t zoned, or if the zones include several rooms, allow the room that needs the highest supply temperature to drive that zone’s required temperature limit. If the hottest supply temperature needed at design conditions is 130°F, there’s simply no reason to ever fire the boiler higher than that.
Put down the calculator, pick up the wrench
Now for the fun part; it’s time to get dirty. The first thing you need to do is determine if the big chunk of iron you’re looking at can even be converted to hot water. Are the sections connecting across the top? If there isn’t a tube across the top, that unit was designed for steam only, as there’s no way for air to pass through the sections and out the air vent that you’ll be installing on the end section.
The next thing to look for is damage. Cracks are an obvious sign, but rust accumulated at the bottom of the section can indicate hairline cracks that you can’t see. In my experience, it’s relatively rare to find a leaking radiator, but it does happen.
There could be a few scenarios that would warrant pulling a radiator apart. Perhaps it’s a big unit with one leaky section, or maybe you need to shorten it for one reason or another. Not a problem, just keep in mind that if the radiator does not have draw rods, it can’t be disassembled and reassembled. A unit with push nipples connecting the sections will always have draw rods. Any radiator with threaded nipples can’t be fixed or changed – at least not economically.
Just one note on draw rods; don’t try to re-use them. Even if the same length is needed, the labor saved by simply cutting them and installing new all-thread rod is well worth the material price.
Valves, vents and steam traps
Probably the biggest change the radiator itself will undergo during conversion from steam to hot water is the addition of an air vent. If the radiator was factory-built for use in either a steam or hot water system, there will be two flat dimples on the end section; one at the top and one halfway down. These serve as places to tap for vents.
If the radiator has never been used for anything but a steam system, the top dimple should be bare. This is where you want to tap the cast iron to install an air vent. If used in a one-pipe steam system, the radiator will likely have an air vent near the middle of the end section. Remove it and plug the hole.
The radiator valve absolutely, positively must be replaced when changing from steam to hot water. Steam valves are made to provide 100 percent shutoff. That’s fine when dealing with water vapor, but when a cast iron radiator is filled with water, there’s risk of freezing if it’s shut.
I’ve gone into homes where radiator sections have cracked as a result of freezing. Hot water radiator valves negate this issue because the seating disk has a small hole, allowing a trickle of hot water to seep through the unit at all times.
If the original system was two-pipe steam, you’ll probably run into a few steam traps. There are two ways to handle this; replace it or gut it. Replacing a steam trap with a return union-ell allows you to easily remove the radiator if needed. Opening the trap and removing the bellows saves time and material costs.
Pipe and proper strainer
There are two more crucial elements to the conversion process, the first of which is getting rid of the old return piping. Any piping component below the water line should be removed to avoid filling the new boiler and circulators with sludge. While flushing the system isn’t bad practice for the supply piping and the radiators themselves, it isn’t an acceptable alternative to replacing the return piping.
A critical element, especially in a system that includes a condensing boiler or ECM circulators, is a good strainer, and a magnetic strainer to capture magnetite. The tight channels in many ModCon heat exchangers can get clogged easily, and the magnet used in ECM circulators is just dying to attract ferrous junk suspended in a hydronic system. Water chemistry is also an essential component with pH, total dissolved solids, and hardness now required tests for system-wide protection and longevity. Last, but not least, the acidic condensate is easily treated by installing an acid neutralizer cartridge.
In summation, there are only three things you need to do to the radiators to change them from steam to water; install an air vent, replace the radiator valve, and take care of the steam trap. To make a conversion live up to its potential, it requires some work on the front end, and attention to the problems that sludge can cause.
But if you do it right, the product can rival comfort and efficiency levels of almost any modern system without ruining the historic value of a building.
Easy button and some ancient history
Converting cast iron radiators from steam to hot water can be a fulfilling task, but it does take time and effort. Luckily, there’s an “Easy Button” if converting isn’t your thing.
U.S. Boiler Company and Governale both sell brand-new cast-iron radiators in various styles. I have a story about these, too.
More than 30 years ago, one of U.S. Boiler Company’s product development engineers called me at the shop. We’d worked together on various projects before, and he knew I had a warehouse full of ancient radiators. He asked me if I had any radiators with ornate scrollwork on them, like you’d see in old, Victorian homes. I did.
He drove to my shop in York from his office in Lancaster, PA, and we walked through the warehouse looking for the most beautiful radiator I had. He found one he thought was perfect, and we disassembled it so he could take the end section back to the plant with him.
That radiator section became the rough blueprint when U.S. Boiler Company and Governale designed what is today the “Classic” and “Victoria” (respectively) radiator models!
By Dave Yates
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Dave Yates began his career in the PHVAC trades in 1972, in York, PA, and owned and operated F. W. Behler, Inc. for 30-plus years. The company is now celebrating 125th year of service. A published author in numerous trade publications in the USA and overseas, Dave has also written articles for The World Book Encyclopedia and operates a consulting firm focused on hydronic heating. He can be reached at dyates@consultyates.com