Unpopular opinion - Riser vents > main vents?

jlbk

I have one 4 story building with no main vents but has 2 risers, front and back, supplying all the heat, and they are tapped and vented. The riser gets hot in 5 mins from the header, and the radiators are hot in another 5-7 minutes. Compared to other properties that I installed a big mouth on, the main gets hot in 2-3 minutes, but it takes another 10-15 minutes to reach the top floor.

The clear answer seems to be to vent these risers as well. This leads to my second question, can i avoid tapping the risers and just tee off the last radiator on the run with a 1/8 tee and add two gorton d? Can the last radiator on the line vent too fast?

Jamie Hall

In answer to your question on teeing off the last radiator on the run for a vent -- that works. And if that vent is before the radiator, while it may alter when the radiator starts to heat, it won't change the rate at which it heats once it starts.

EBEBRATT-Ed

@jlbk

If I understand you system correctly you said you have two riser that carry all the heat. If this is true the top of the risers is basically the end of the main.

The second part, if you mean adding more venting to the top radiator I would not do that the rad may overheat. Try it if you want but I would vent the radiator inlet and leave the radiator vent alone

jlbk

Yea right the riser is the end of the main. So wouldn’t all risers technically be the end of the main then? Wouldn’t tapping vents on all risers be just as important if not more so than having a main vent?

New England SteamWorks

Install a regular main vent at the top of the risers, not an 1/8” radiator vent. Do so by replacing the angle valves on the top radiators with a tees, then connect to the radiator with a straight valve. 

bburd

Steam flows through pipes due to pressure differential, not gravity.

jlbk

I agree installing a main vent on the riser or the valve is the proper way to do it, but can I take the easy way out by doing a 1/8 antler out of the radiator tapping? 

ChrisJ

Hmmmmm

ethicalpaul

There is a lot of mixing of ideas in your paragraph, @betweentheframe. @bburd said it so plainly and correctly above.

Steam in a riser pipe is not really like warm combustion gases in a chimney--the chimney is open at the top and bottom. But that's really beside the main point:

The movement of steam in our pipes is vastly (might as well say completely) due to pressure differentials between the boiler which is producing steam (and increasing pressure) and all the pipes in the system. The pressure increase moves in waves until it (and the air in front of it) finds a way out. That is where the steam will go, whether it's up, down or sideways.

Edit: PS:

pressure exists because of gravity

Atmospheric pressure does, but not all pressure does. An oxygen tank and supply line in space works with no gravity.

ethicalpaul

jlbk said:

I agree installing a main vent on the riser or the valve is the proper way to do it, but can I take the easy way out by doing a 1/8 antler out of the radiator tapping? 

An easier way out that will keep your radiator heating at about the same rate as it does today would be to use a tapping on the same side as the supply pipe. Put a #D or #1 size (using MoM or Gorton sizing numbers) on that tapping, and put a nice slow #4 on the (normal) opposite side tapping. Many radiators have tappings on both sides with one of them plugged.

Gsmith

Another factor not mentioned is the pipes and radiators condense the steam to water at 1\1700 the volume which creates a vacuum drawing the steam towards the cooler (than steam) radiators. Helps a lot with the distribution once the steam gets to the rads.

ChrisJ

@betweentheframe. So you feel the difference in weight between steam and air is enough to push the air out of the vents at the speed it does?

I calculated the pressure drop in my piping to each radiator and oddly enough it's roughly what the boiler runs at.

I'm sorry but, if you have a single pipe system with air vents it's not running at 0 psig.  Either your gauge isn't sensitive enough and or its been pulled into a vacuum by a pigtail.


Mine runs no lower than 0.009 psig which is the pressure drop to the furthest radiators.


And no, I do not feel the weight of the steam is having an effect.   The steam condensing and creating a vacuum does though.  Even in my mains as the steam "inch worms" down the pipe.

ethicalpaul

I don't want to hijack this poor thread any more, but there's a lot of wrong things here I'll address just this one more time, then if you want to discuss it more, start a new thread called something like "why steam goes where it goes" or something and I'll find it

That’s a half truth:..If you remove all rads and have nothing but steam pipes coming out of the floor (or as when system is cool and valves are open) you will have a zero pressure system,

No you won't. You'll have a greater pressure in the boiler, which then pushes the air toward the places with less pressure just like I described before. That could be up, down, or sideways

but the steam will still move up and out of the pipes because it is lighter than the air.

No. It will move out of the pipes because steam is being generated behind it, builds a small amount of pressure and starts pushing it. Up, down, or sideways.

When the vents are all open when a boiler fires up there is no pressure, the steam displaces the air because it rises.

No. The steam does make pressure (yes at first a very small amount, but more than enough to overcome any gravitational effect. And it pushes the air out of the pipes, up down, or sideways.

It will not work wether it is up or down, because the steam is lighter than air, yet alone water, which is why you have to have the rads above the water line.

It will absolutely work whether it's up or down. The reason rads are above the water line is so that the radiators don't fill with water.

Air becomes more dense than steam above 324F and it becomes more complicated. But it is essentially true that hot air(steam is a gas) rises.

In an open space, the less dense stuff rises. But in a closed system, it's pressure that rules the day. And you're right...it's also pressure that makes warm air rise in a room. But there's no pipe to guide it, so it just rises.

ChrisJ

betweentheframe said:

Atmospheric vented steam systems are not closed systems. That is my point! Until all the vents close!

That's good and all, but steam isn't going to climb past it self in a closed pipe full of steam. 

You can have a single pipe system 99% full, but with all radiator vents still open and air vs steam weight isn't going to have an effect on that.

ethicalpaul

betweentheframe said:

And no offense but a thread about riser main vents and “main” vents is the appropriate thread to discuss where steam goes and why, and you can tell someone else where they can and can’t discuss the said topic. 

I said I wouldn't respond more. (but now I have broken my word). You can keep posting wherever you like of course. But if you want to talk to me more on this topic it will have to be on a different thread from the poor poster who just asked a question about his vents

bburd

@betweentheframe, you wrote:

“ I’m just an idiot with a boiler, but if it wasn’t this say you’d put the boiler in the attic”

Some tall buildings with steam heat do put the boilers in the attic, and use pumped condensate return. It works fine.

This makes rentable square footage on each floor of the building available that would otherwise be dedicated to a chimney shaft.

jlbk

Hah, I came to check on my thread after a day and I saw 14 new responses. So sad that none of it had to do with my question. 

jlbk

Ethicalpaul, how do I remove this plug? Just drill it and thread it? Or is there an easier way?

ethicalpaul

So you did see my reply in there 😅

And you do have the vent port plugged on the pipe side, then?

Some can be unscrewed, some must be drilled. Can you post a photo of it? 

EBEBRATT-Ed

I am having a senior moment.

Whats the steam system where they send the steam main off the boiler straight to the attic. Then the main circles the attic with tees with branches dropping off the main feeding down to the radiation?

It was designed by a guy that worked for HB Smith. John "something" It's described in the LAOSH

bburd

I believe that main pipe from the boiler to the attic is called an “express riser”.