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steam or hydronic?


John Dirks Jr
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I'm scratching my head over an old boiler. The Baltimore row home was built in 1931. The boiler had no sight glass indicating a steam system, and no circulation pumps indicating a water circulating system. The piping was large in diameter which makes me lean towards steam.

I thought steam systems had to have a sight glass. Is it possible to have a steam system without a sight glass? What am I looking at here?

When I engaged the thermostat, the burner responded and fired up. It ran for about minute then cut out. That's all I could get out of it.

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I'm thinking this thing was originally coal fired and then converted to oil.

No sight glass.

No circulating pump(s).

???

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When I first started inspecting, there were a lot of old gravity hot water systems here, and believe it or not, they heat up almost as fast as a circulated system. Also, the expansion tank is a giveaway. A steam system has no need for an expansion tank. Air (steam) is compressible, but water is not. Hence, the expansion tank. When water heats up and expands, it needs somewhere to go.

Now, I should back up and correct myself slightly. Many steam systems are converted to hot water, so don't be fooled if you see large distribution pipes with a hot water system. In such a case, you are looking at a steam system that has been converted to hot water.

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I'm thinking this thing was originally coal fired and then converted to oil.

Maybe, but I doubt it. Richmond is boiler land too. There's a ton of them downtown (Inspected two this week already). Most of the steam is gone now. In fact, come to think of it, I bet it's been eight to ten years since I've seen a steam system. At any rate, the old vintage oil burning boilers always have those big service doors to make a thorough cleaning easy. Imagine that... But, they're not very efficient.

The original oil burner assembly for that boiler was huge in comparison to what you see there - probably 1/3 bigger.

And, yes, steam will always have a site glass because water level is critical.

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Why would the burner cut out after a minute? The fuel oil tank was full. It had a safety sensor on the flue. I opened the refractory door for a second or so while the flame was burning. Could that have triggered the draft device to shut the burner off?

Opening the door wouldn't. Typically an oil burner cuts off if it isn't experiencing consistent fuel flow and flame. If the tank was allowed to go empty and was just filled, the fuel may be contaminated by all the crap that was on the bottom. (It's best to never let the tank get too low, and, if it does, you need to leave the boiler off for a few hours for the crud to settle down. Once the jets in an oil-burning system get crap in them, that's all she wrote. It will run like a dog until the filter is changed and the jet is replaced. This is so critical that, as a disaster restoration contractor, I dealt with many a back-puff (a disaster where the oil burner system soots up the entire house with black oily soot - big money to undo - a mess! Thousands of dollars.)

Also, the burner is controlled by a temperature sensor. When the water gets to the prescribed temp, it shuts down until the water temp drops a few degrees and then repeats the process. Next time one cuts out on you, try hitting the reset button on top of the transformer. If it fires up again, you're low on fuel or the fuel's contaminated. An oil-burner won't run more than about maybe 15 seconds without a good flame, to avoid a flash fire in the firebox.

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Next time one cuts out on you, try hitting the reset button on top of the transformer. If it fires up again, you're low on fuel or the fuel's contaminated. An oil-burner won't run more than about maybe 15 seconds without a good flame, to avoid a flash fire in the firebox.
And is that why you only hit reset once?[:)]

Thought I'd add that little precaution.

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No, it was originally a coal fired gravity hot water system, and now it's an oil fired gravity hot water system.

The big pipes are so large volumes of water will circulate; skinny pipes are a modern phenomenon.

You should be able to tell whether it's hot water or steam by the radiators, not just the boiler and controls.

A one pipe steam system will have a vent on the radiator, and a single pipe. A two pipe steam system will have the supply pipe enter on the high side, and the return on the low side, and there will be a steam trap.

I'm too tired and burnt out to attach all my pics; just google it up and start downloading.

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No, it was originally a coal fired gravity hot water system, and now it's an oil fired gravity hot water system.

The big pipes are so large volumes of water will circulate; skinny pipes are a modern phenomenon.

You should be able to tell whether it's hot water or steam by the radiators, not just the boiler and controls.

A one pipe steam system will have a vent on the radiator, and a single pipe. A two pipe steam system will have the supply pipe enter on the high side, and the return on the low side, and there will be a steam trap.

I'm too tired and burnt out to attach all my pics; just google it up and start downloading.

Indeed, You're right, I had forgotten that gravity water systems also have large distribution pipes. Am I correct that steam is always large diameter pipes? I don't ever recall seeing small pipes on a steam system.

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What is correct is pipes sized to the output of the boiler and the capacity of the radiators.

That usually means big pipes, but "big" is kinda general. There is no *one size fits all* approach to steam systems.

The thing to remember is these were engineered systems. When you see alterations to the pipe sizes, that usually means it's been screwed up by a hack.

If you look closely at steam pipes in the basement, you'll notice they have nice step downs (like a well designed duct system), and the pipes will have a sweet little 1/8" drop per foot to get the condensate back to the boiler. Change the pipe, you change everything.

Baseboard radiators retrofit to steam systems usually don't work either. They can work, but it's unlikely they'll work well. Usually they just corrode up and fail.

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The thing to remember is these were engineered systems. When you see alterations to the pipe sizes, that usually means it's been screwed up by a hack.

If you look closely at steam pipes in the basement, you'll notice they have nice step downs (like a well designed duct system), and the pipes will have a sweet little 1/8" drop per foot to get the condensate back to the boiler. Change the pipe, you change everything.

Boy, either it's never been put to me quite like that, or I've forgotten it. That's good info. Thanks.

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The original gravity water system would have had a steel tank in the attic for expansion of water and overflow. These usually were piped into the gutter system from the attic. Some of these "expansion" tanks had site glass tubes on them so be careful not to confuse them with steam. Kurt described the radiators as the best way to identify what you have.

Now that the system has a basement expansion tank it has simply become a hydronic system, and although it will work, it should have had a circulator installed when converted. The natural flow of water, (cold to hot) on an open system worked/works better than the same system closed, without a circulator.

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Now that the system has a basement expansion tank it has simply become a hydronic system, and although it will work, it should have had a circulator installed when converted. The natural flow of water, (cold to hot) on an open system worked/works better than the same system closed, without a circulator.

Could you show us something from a credible source stating that the flow of water "worked/works better" in an open system? This has been discussed by some of the top steam heating gurus in my area and they think it's folklore. The only changes to the system are installing a compression tank in place of the expansion tank and a relief valve is installed in place of an overflow pipe. How does this have any effect on the rise/fall of hot/cold water, that quickly become a convective current.
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Originally posted by ghentjr

Could you show us something from a credible source stating that the flow of water "worked/works better" in an open system? This has been discussed by some of the top steam heating gurus in my area and they think it's folklore. The only changes to the system are installing a compression tank in place of the expansion tank and a relief valve is installed in place of an overflow pipe. How does this have any effect on the rise/fall of hot/cold water, that quickly become a convective current.

First, I am talking about gravity hot water, not steam. The two are not closely related. I am not sure who your guru's are and how much gravity hot water they dealt with.

The way it was explained to me many years ago by my mentor was that the open system on an original gravity feed had no resistance and allowed the flow of cold to hot/hot to cold without any impediment. The moment heat was applied to the water in the boiler it started to move. The water expanded (heat rises) to the attic overflow and moved freely with the slightest amount of heat. The addition of an expansion tank and pressure relief valve created a "pressure head" that the gravity flow action had to overcome. Water did not move as quickly. It (heated water) had to get to a temperature that allowed movement against the pressure head especially without a forced movement from a circulator. With a pressure head and a restricted water flow, it took longer to get the same results. (My guru on hydronic and steam was Tom Byrne, now deceased, but one of the best and most knowledgable guys dealing with wet heat.)

This was something I subsequently confirmed by my 30 plus years inspecting in a wet heat area with many gravity feed systems some of which were still burning coal.

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