One or Two pipe? Nice Radiator

That's probably a Moline system

the key-operated valve on the return connection is a very common Moline feature.



The Moline is a Vapor system designed to run on ounces of pressure, or sometimes in vacuum. The company that made it was based in Moline, IL, and it's unusual to find one this far east. Dave Bunnell, "The Steam Whisperer" is our resident Moline expert and I hope he will chime in here.



Assuming this is a Moline, the lack of an air vent on the radiator is not an issue. These rads are not supposed to have vents. Along with the condensate, the air is vented out the return connection and thru the "dry" (overhead) returns to a central point in the basement. At that point, there should be a long pipe or a ceiling-hung rad used as a condenser. After that, a vacuum valve let air out but not in, so as the coal pile burned down, the system would go into vacuum and continue generating steam at lower temperatures. The water was returned to the boiler at this point, by gravity.



The question of whether to convert something like this to hot-water is like the zombie that refuses to die. The answer is, only if you love living dangerously. This system was designed to run on ounces of pressure, but hot-water in the same building will easily exceed ten times that pressure. If there are any weak places in the piping or radiators, they WILL leak, and the lawyers will hold you responsible for fixing the damage.



Then there is the issue of whether the rads will produce enough heat on hot-water. Assuming they will, you will have to run them at such high temperatures that a condensing boiler will be out of its condensing range for much of the time. There goes the promised fuel savings.



It's much more economical and much less risky to fix whatever might be wrong with the steam, and put in a new, more-efficient boiler. This will put you very close to the efficiency of hot-water, for much less money, effort and risk.



This system has probably worked for close to a hundred years, and with proper care will outlast all of us. Take some more pics and let's have a real good look at it.

That boiler is not a snowman

it's a cast-iron sectional boiler. A snowman would have been round, would not have had a jacket and the asbestos would have been applied as a covering. But there is probably asbestos inside the jacket on that one.



I've attached a pic of a snowman we replaced some time ago. You can see why we call it a snowman. It's also known as a pancake boiler, since the sections that sit on top of the firebox are shaped like pancakes.



The snowman is also one of the least efficient types of boilers ever made. One of my Dead Men's Books says these boilers are typically no better than 40% efficient on oil, and I would assume they do as badly on gas. The reason is the lack of heat-transfer surface and the rather short path of the flue gases thru the boiler. This results in some outrageous stack temperatures.



The boiler in the pic would do much better than a snowman, especially if there were proper baffles in the flue passages, but it's no match for a modern steam boiler. When you replace the boiler, you can probably use at least some of the existing header for the new one- whoever built that header looks like they knew their stuff.



The Moline equipment, if it's still there, is probably up in the ceiling. I hope you can get back there and take more pics! There is no need for a condensate tank and pump on this system- keeping the pressure low is all that's needed. The new boiler should have a Vaporstat that cannot be set higher than a pound. A Pressuretrol is wrong for this system.