Two-pipe, air-vent system...what do I need to know?

SpeyFitter

All-

I'm a new homeowner, facing a steam heating plant for the first time. The existing boiler is the original Gurney installed in 1930, which was converted from coal to oil at some point along the way. I respect the fact that it's been steaming away for almost 80 years, but it's got to go. Once the winter's over, we're going to replace it, along with having someone do a thorough examination of the whole system, since the second and third floors are much colder than the first.

This is obviously not something I'd try to do on my own, but I got a copy of "We Got Steam Heat" so that I'd know enough about how this system works to be able to tell if the heating guys giving me estimates knew their stuff. The problem is, the book doesn't really mention 2-pipe air vent systems. If I hadn't come across Dan's article about the building on 5th Avenue in New York that had this system, I'd probably still be thinking that I needed to remove all of the air vents from the radiators!

Anyway, are there any special considerations when dealing with a 2-pipe air vent system? I just don't know what's "normal" with a system like this. For example, I can't find any main air vents anywhere on the pipes in the basement. From the book, I know that with either a 1-pipe or true 2-pipe system, that'd be bad news, but is that bad on a 2-pipe air vent system? Is the "as little pressure as possible" rule still applicable to a system like this?

Thanks in advance for any help or information you can provide!

-Craig

Dan C.

Steamhead,
It has a valve on the supply and return and then each return drops down to form a trap before it goes into a return main. It looks like the air vents were always there. I don't think anyone added them. It's all covered in asbestos so you can't tell what it is.


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Steamhead (in transit)

If the house was built in 1930

it's probably not an air-vent system, or at least not supposed to be. It might be a Vapor system (the variety of 2-pipe generally being installed at that time) to which someone has added improper air vents. We see this frequently.

A true 2-pipe air-vent system generally has a hand-operated shutoff valve at the return as well as the supply of each radiator, and an air vent on each one. Note that there was at least one Vapor system (Moline) that had a return-side shutoff, but this was generally operated by a key rather than a handle, and of course no radiator vents. Post some radiator pics if you're not sure what you have. Post them anyway, we love this stuff!

If it really is 2-pipe air-vent, do NOT vent the return lines from the radiators. These lines are not supposed to have steam in them. Vent the mains well, and keep the system pressure low with a Vaporstat. If you want to use thermostatic radiator valves, get the type that replace the air vent rather than the steam shutoff.

Once the proper vents are in place, it will work a lot better.

When replacing the boiler, don't use any contractor who sizes the new boiler to the same capacity as the old one, or proposes to use copper for steam piping.

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Dan C.

Steamhead, It has a valve on the supply and return and then each return drops down to form a trap before it goes into a return main. It looks like the air vents were always there. I don't think anyone added them. It's all covered in asbestos so you can't tell what it is.



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Steamhead (in transit)

OK, that confirms it

and I'd also bet it's much older than 1930. Gurney became part of National Radiator Corporation in 1928, well into the Vapor Era. Go here for a 1928 ad regarding this:

http://www.heatinghelp.com/pdfs/532.pdf

If your radiators have a lot of ornate decoration in the iron castings, they would have to be older than about 1920 since this type of radiator went out of production around that time.

That water seal ("trap") on each return you mention showed that the installer knew his stuff. The seal keeps steam from leaving one radiator and entering another one thru its return connection. In order to keep the water from being pushed out of the seals, you must keep the pressure low.

Where are you located?

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Craig Garnett

I'm pretty sure I'm looking at a 2-pipe air vent system. Both the supply and return pipes are attached at the bottom of the radiators, the return pipe is only slightly smaller than the supply pipe, there are hand-operated valves on both sides of all of the radiators, and there's an air vent on the return side of each radiator. I've attached a picture of the boiler and a radiator from the home inspection report, but I'll fire up the camera over the weekend and get some better shots.

The radiators, although covered in several layers of paint, are all pretty plain. On the second and third floors, they are tall, HB Smith Princess models, while the ones on the first floor are smaller...haven't been able to read the markings on them yet.

I'm north of Boston. I found Dan C through the website and he was kind enough to come over to take a look at the system and is working up an estimate for what needs to be done. I hadn't noticed those weird U-shaped traps in the basement...I was still stuck at not being able to find any main vents. The traps all have little test nipples at the bottom of the U.

If I remember correctly, the boiler has "Gurney 456D" cast into one of the chamber doors. Its possible that when they built the house they brought in an older boiler, but the 1930 date on the house is right from the paperwork I've seen.

Thanks!
-Craig

Steamhead (in transit)

Those Princess radiators

had been discontinued by 1930, as far as I know. The one in the pic looks like it might be a Smith "144" or similar large-tube unit. This was the current type of radiator for 1930. So that floor may have been remodeled at that time.

It's possible the date of 1930 was when the house first appeared on the town or county tax records. We find that a lot around here.

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Craig Garnett

Steam plant pictures

Steamhead-

You want pictures, you got pictures! I was wrong about the boiler number, it's a 445D. Can't find any information on when that model was made, though. I've given the pictures names describing what parts they're of.

Thanks!
-Craig

Steamhead (in transit)

Impressive!

but I can't find a manufacturing date on the boiler.... however, those old round boilers were typically no better than 40% efficient on oil according to one of my old books. If that holds true here, you could theoretically cut your fuel usage in half with a new boiler.

The best residential oil-fired steamer out there now is the Burnham MegaSteam. Here's a pic of one we installed.

As for the rest of the system, keep the pressure low with a Vaporstat and vent the heck out of the steam mains. Then watch how well it works!

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Craig Garnett

I can believe that the efficiency is really low. As I told Dan C when he was here, the warmest room in the house is the boiler room when that thing fires up!

We've got a gas line in the house already, so we are planning to switch over to gas and get rid of the two oil tanks. That would probably mean going to a Burnham Independence, to take advantage of the deal that National Grid is offering. I'm just glad that you no longer have to have the National Grid offer installed by one of "their" contractors. I'm sure that some of the guys who National Grid has signed up to do the installations know what they are doing, but I'll feel a lot better having someone from here who obviously knows their stuff do the work.

-Craig

Steamhead (in transit)

If you go gas

don't use an atmospheric boiler like the Independence. Atmospheric boilers lose a LOT of heat out the base, and their burners must run with more excess air which sends more heat up the chimney. AFUE doesn't take this into account, which is why we regard it the same as EPA gas-mileage ratings. Now you're getting the idea of why National Greed likes atmospheric boilers. Our utility does too.

You will gain about 6-7% better thermal efficiency (before AFUE is even calculated) by installing a wet-base boiler with a power gas burner. The wet-base surrounds the flame almost completely with cast-iron having water on the other side, so it will absorb more heat. And the power burner- which looks like an oil burner and operates in a similar fashion- mixes air and gas more efficiently so less excess air is needed for clean, safe combustion.

Burnham doesn't offer the MegaSteam with a gas burner, which severely limits the market for this excellent boiler. But the Slant/Fin Intrepid and Smith 8 boiler series are factory approved to run gas as well as oil. This also means you can switch fuels without buying a new boiler. I've attached pics of one of each brand that we've installed.

There are two other things to look at before switching fuels: 1- oil suppliers are in competition so you can choose the one you want, but gas is basically a monopoly even in "deregulated" areas. So if you can only burn gas and the gas company raises their rates, you're stuck.

2- if you already have a gas line, don't count on using it as is. It may not have enough capacity to run a boiler as well as everything else you have that burns gas. If this is the case, who pays to replace it?

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