how to tell a steam boiler from a hot water boiler

Ok, dumb question: How do I tell if my house's boiler and heating system is hot water or steam? I'm confused because I've had 3 plumbers in for estimates to replace my boiler - 1 says it is steam, 1 says it is hot water, and the 3rd wasn't certain but thought it was hot water. I'd always thought it was hot water, but I want to be certain.
My house has an old cast iron Ideal Redflash boiler from the American Radiator Company (which changed names in 1929 the year our house was built, so I'm pretty sure this is the house's original boiler) that I believe burned coal originally but now burns oil. There is no sight glass on the boiler, which makes me think it is hot water, but I also can't find any expansion tank, which makes me wonder (I've checked all closets, attic, etc. - where could it be hidden?). The psi on the system is around 15, which also makes me think it is hot water (too high for residential steam). The radiators around the house are all old cast iron 2-pipe jobs.
How can I figure this out for sure?
TIA
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Does it have a sight glass?
Can you post a picture here? http://forums.invision.net/Main.cfm?CFApp=2

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No sight glass. And forgot to mention that there's no circulatory pump - it's a gravity system. I cross-posted with a photo at http://forums.invision.net/Main.cfm?CFApp=2
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I'm not an expert but I would look first at the radiators. If they have a steam release valve, they are steam. If they are closed loop, that says hot water regardless of shape. A single pipe definately says steam but two pipes could be either.
Does the system also supply residential hot water for the tub and sink. If so it probably is not steam but there may have been hybrid systems way back when

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The radiators look to be designed for hot water. They are 2-pipe, have horizontal cross-pipes at top and bottom, the inlet and outlet pipes typically connect to the bottom of the radiator (although on a few the inlet pipe connects to the top), I do not see any steam traps, and there's a small valve (but not a relief valve) on the top of every one typically located on the side opposite the inlet pipe that I believe can be used to bleed them.
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You're probably right, its hot water but the radiators sound like they could have been configured for steam (or converted from). The small valve sounds like it is in the same place as the steam trap would have gone. In a steam system, steam enters from the top and condensed water drains from the bottom by gravity.
Easy way to tell is open one of those little valves while it is running and see if water or steam come out.
Regardless, if you are seeking to replace the boiler, it dosen't really matter what it was unless you also plan to reuse the radiators in which case you only need the plumber to evaluate them and their pipes. With the given radiators, you may be able to go either way though I can't imagine wanting a steam system.

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I like steam. It probably makes no difference in a typical house, but in a large building steam has many advantages in distribution over water. Steam moves a lot of energy in a very compact and efficient manner. No pumps are needed (exceptions being condensate pumps in some systems) Steam can literally be moved miles in pipes to heat large buildings a distance from the steam plant.
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15lb, no sight glass, its hot water.
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wrote:

steam certainly has advantages.
Some times steam is noisy, hissing or iirc even banging. Hot water is quieter, never made any noise in the ttwo years I lived in a 3 story converted mansion, one year on the 3rd floor, one year on the second. May have to be bled every year though. Each radiator, starting with the highest iirc. Easy enough, but the kind of thing a procrastinator or depressed person might not do.

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Aren't they good?
I just got back and saw the post. You've got a dinosaur in your basement, but it won't decompose into oil.
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Sounds like water. Residential steam is less than 1# usually, should have a sight glass, and you'd hear some hammering in the pipes on occasion when it starts up.
Love those old cast iron radiators. Wish I had them.
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wrote in message >

Resi steam _should_ be under one pound. Higher pressure is actually bad in a steam system
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On Fri, 12 May 2006 18:05:33 -0400, "HeatMan"

I really don't know: Is 15 the operating pressure or the maximum possible pressure before it explodes?
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Low pressure boilers are usually rated at 15 psi steam, 50 psi water. That is a maximum, not an operating pressure. When you get above 15 psi, it is considered high pressure and many states require a license to operate. There should be a relief valve set to the maximum pressure. There should be a sight glass and low water cutoff float switches.
We have a large four story building at work. We operate at about 5 to 8 psi and easily move steam hundreds of feet. Residential is usually less than 1 psi. Industrial use can be 100 to 300 psi and steam can be moved long distances, then reduce for use.
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wrote in message >

Boilers are tested at (I think) 4 to 5 times operating pressure as the max pressure. Otherwise Edwin is correct.
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http://en.wikipedia.org/wiki/Hydronics#Two-pipe_steam_systems
general stuff: http://toad.net/~jsmeenen/hydronic.html
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