why does this vent work?

John Shea

Below is a picture of my home's steam boiler/near-boiler piping.

I understand the (1927) piping is incorrect, but you know the old saying "if it ain't broke..."

I really don't have any problems with the system, other than the boiler is a little undersized after a 4 radiator addition. (going to try to squeeze another year out of it)

My question is how can the Main air vent get steam to the end of main, when the vent is so close to the dry return and/or equalizer?

What prevents the steam from traveling through the header drip (equalizer?) to the vent and shut it after traveling just 8-10 feet? or is that what's happening?

Steam gets through to the end of the main relatively quickly, but not sure if it's as quick as it should.

Any thoughts/recomendations will be much appreciated.

Ken_8

I guess we can assume...

there's no true hartford loop?

It probably works because the equalizer pipe and return leg will back up with slight boiler pressure - blocking the drip from shooting steam or air (on start) into the vent, thereby forcing most air to go through the main only.

There are actually three obvious problems here.

1) Never put the vents on the run of a bull-headed tee.

2) The hartford loop should be 2" below the NOWL not 2 feet above it.

3) The condensate return should always be piped into the boiler return below the water line.

After 70+ years however, who's gonna change it now?

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John Shea

No, no hartford loop.

What's NOWL?

I may think about re-piping when I need a new boiler (it was leaking when I bought the house seven-years ago. I replaced a rusted-through threaded rod that held the sections together, and tightened a few turns every day for a week and it's been golden since Ha Ha!)

Thanks for the tips. In the meantime, would it do any good to put the vent up on a 8" nipple or so? maybe with a couple of 45's coming out of the bull-headed tee?

Ken_8

Nope.

Raising the main vent will minimally improve what you have.

NOWL = normal-operating-water-line

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Steamhead

John, how long is your steam main

and what pipe size is it? With this info we can tell you if that Hoffman #75 is correct. Also, is this the only steam main in the house?

Hint: The insulation used on your pipes was normally 1-inch thick. The walls of the pipe are almost certainly 1/8" on either side. So subtract 2-1/4 inches from the outside diameter of the insulation and that should be your pipe size.

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John Shea

The system's got one 2" steam main (basically loops the perimeter of the basement) about 75' long.

However, now that I'm thinking about it, we added a 2" riser to supply an addition (4 radiators). I did intall a smaller main vent Hoffman 1A I believe, at one of the new radiators to get better distribution to the addition. It seems to work pretty well.

I am aware, however, that the boiler is now slightly undersized (via the addition) and will need a larger capacity boiler (eventually) to get good heat through all radiators. It puts out 120,000 btus and based on my calculations, I need 150,000 to heat the whole system.

Thanks Steamhead!

Christian Egli

It may be that there is a check valve just before the dry return reaches the equalizer. It seems there is a little bulge in the insulation?

The check valve would let the water flow back to the boiler but prevent steam from going in the opposite direction. The stacked height of the accumulating water is what would overcome the pressure differential and open the check valve.

It is all 2 ft above the current boiler. Do you have any idea of what was there 70 years ago?

John Shea

I have no clue what was originally there.

Thanks for the tip. I'm going to remove a little insulation and see if there's a check valve there.

Steamhead

To vent that main

install two Gorton #2 vents at or near the end. Then watch how well it works. If the addition riser is slow, you can add a vent at the top. The vent size will depend on the height of the riser.

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John Shea

Piping's the problem.

Thanks Steamhead. I had a spare Hoffman #75 so I added it (doubling the previous venting rate). It made no difference whatsoever.

I think it's because of the near-boiler piping. (I could probably put 4 Gorton #2s and the system wouldn't heat any better)

This spring, I'm going to attempt to install a new (correctly sized) boiler and repipe the near-boiler pipes.

I will then replace the Hoffmans with two Gorton #2s.

Thanks again.