Proper steam firing duration

Bob Bardoorian

Our house mentioned elsewhere was a coal fired two pipe steam system and "state of the art" in 1925. I can tell you no corners were cut anywhere in construction. If coal boilers were "on all the time" and the systems were designed for this, after converting to oil, a cycle on/cycle off situation along with thermostats became normal. However, what is better, and more fuel efficient, a longer adequate burn, or a hotter shorter burn?
We use an advanced Honeywell steam capable setback thermostat currently on adaptive settings, as we both work.
This all points back to nozzle size as mentioned in my other thread.
Bob

Steamhead (in transit)

Venting is key here

your oil-fired boiler comes on full blast, as opposed to a coal fire coming up gradually. So you need to make sure the steam mains and dry returns have enough venting.

You have a Dunham Vapor system- these systems typically used crossover thermostatic traps to vent the steam mains. Many times this is enough, but if the mains don't vent completely in a couple of minutes you need to add main vents.

Typically a longer burn is better, but if the steam doesn't distribute quickly that long burn doesn't do much good.

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William Faust

just to clarify

Okay, so I understand now that air had more time to vent with a coal fire that came up more slowly than fuel oil or gas. Do I correctly gather then that there would be no downside under ANY circumstance to installing vents past a 2-pipe system's F&T traps and/or on return risers in order to maximize venting speed?

Steamhead (in transit)

Install them before the F&T traps

so the vent opening in the F&T doesn't restrict the air flow to the vents.

On your system, the dry returns should vent thru the boiler-feed tank.

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William Faust

I blew it

Incidentally, I just repaired or replaced my F&T traps. I was disappointed that the Barnes & Jones replacement has no drain plug at the back like the Hoffmans - seems like a poor design from a maintenance point of view. Anyway, your response seems to indicate that I could potentially further optimize air venting by installing main air vents before the F&T's.

Given my feeder boiler air vent, there would be no good reason to vent the base of the return risers?

Steamhead (in transit)

That's right

as long as the air can flow unrestricted from the return risers to the feed tank.

Move the steam main vents and watch how much faster the mains vent.

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William Faust

No vents here

Frank - I don't have any steam main vents to move -- the only vent in the entire system is at the boiler feeder. But I can place vents at the ends of two steam mains where there is a capped nipple in each instance.

On a slight tangent, my 2-pipe system was installed in 1949. 1. Do I correctly understand that it would not have been pumped in those years? If yes, would there have been any reason for the gravity system to have had F&T traps? This is something that I have never understood. 3. Lastly, again assuming that it was originally gravity, wouldn't there have HAD to have been steam main air vents whether or not it had F&T traps? If so, I'm guessing that the steam main air vents were at the above-mentioned capped nipples.

Fred Harwood_2

Venting

Bill, low pressure steam (vapor) needs no pumping if you control the pressure with a Vaporstat to less than 1 PSI, the equivalent of 28 inches of water column in the returns, and your returns have that much drop to the boiler water line. A Pressuretrol cannot control the pressure that closely, so past conversions used F&Ts and pumps to get the water back into the boiler at more than 1 PSI.
If your system piping was designed to operate at less than one PSI, then you could go gravity, all else equal.

I don't understand, however, if you have radiator and mains traps in your two-pipe system, why you have a F&T at all.

Steamhead (in transit)

I've seen that system

at some point, radiation was installed in the basement well below the boiler's waterline. So in that configuration a pump was needed. If that were my house I'd dig a pit for the boiler and eliminate the pump.

Bill, you can use those capped takeoffs on the two mains for vents, and drill and tap the third one.

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