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New (Old) House - Vent Question


Purchasing an old house and new to steam.  The boiler (an old Byrant - estimated at 40 years old) seems to work fine, but appears to be slow at delivering steam to the radiators.  During a test fire today I'd estimate that it took 30 minutes for the first few radiators downstream of the header to start getting warm.

After the initial 30 minutes, all the radiators started getting hot, but the far ends (one pipe system) stayed cool far longer.  Not sure what my expectations should be here.

My suspicion (given my reading of of this fine website) is that the radiator vents are clogged/not working and need to be cleaned or replaced - house has been vacant for 3 years and no one who could vouch for the maintenance of the system is presently alive to tell me.

Any advice on how to NOT snap off the vents in the radiators?  I was planning on slow steady pressure, with perhaps some liquid wrench..plus maybe some heat.

Lastly, in terms of a main vent, there appears to only be ONE..located at the end of the return where it takes a 90 degree turn from the horizontal down towards the boiler.

From what I've read here, I want to have the main vent (and potentially more than one) in the supply leg to speed the movement of steam up towards the radiators.



  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    edited September 2012
    Main vent location

    Chances are the radiator vents are ok, so check the main vents first. With the boiler switched off, remove the main vent, and try to blow through it. A soak in vinegar will sometimes bring them back to life.

    The main vent will do a good job located in the dry return before the elbow which goes down to the wet return. If the vent is on that tee, then protect it with a few elbows in a menorah to slow down any water-hammered slugs of water coming back up the dry return.--NBC
  • a3inverter
    a3inverter Member Posts: 64

    I will start with the main vent and work from there.
  • Rod
    Rod Posts: 2,067
    edited September 2012
    Main Vents


         While Liquid Wrench might work okay, I would recommend  Kroil by Kano Labs It’s available on Amazon or directly from Kano Labs.  http://www.kanolabs.com/

    I’ve found it quite superior to most other penetrating oils especially on rusty threads. I would apply it several days in advance to let it soak in well.  I wouldn’t use heat on old cast iron radiators. It isn’t worth the chance of cracking them.

           How many steam mains do you have? You need to have Main Venting on each steam main.

    NBC mentioned putting the vent(s) on an “Antler” at their present position.  I’ve attached a drawing below . Mounting the vent on a plugged tee allows you to easily add another vent if necessary. While the pipe union isn’t necessary, it allows you to easily install or remove the vents for servicing.

           If you can give us the size of pipe and the length of the steam main(s) we can calculate how much venting you need.  The most common main vents used are : The Gorton #1, The Gorton #2 and the Hoffman #75. Venting capacity wise:

    3 Gorton #1 (s)        =  1 Gorton #2

    2 Hoffman #75(s)    =  1 Gorton #2

    These vents are available from your local supplier or can me got at Pex Supply http://www.pexsupply.com/  on the internet.

    With good main venting, ideally the steam will quickly fill the main  with steam to the last radiator before it begins to enter the radiators. Unlike radiators you can’t over vent the mains.

    I would get the main venting working properly first and then tackle the radiator venting.

    - Rod
  • a3inverter
    a3inverter Member Posts: 64
    One Steam Main (?)

    I believe I just have one steam main.  A single steel pipe comes out of the boiler and then forms a ring around the entire basement, with junctions going up to each radiator (1930 2-story dutch colonial...about 2100 sq ft with 750 sq ft of radiation).  Some are 1 pipe, some are 2 (they have a pipe connection on either end with no valve).

    At the end of the ring in the basement, it takes a 90 degree turn from horizontal to vertical then down into the boiler.  There is a big vent (the main vent IIRC) at the 90 degree turn.

    I won't be back into the house until next Friday, but will take measurements then.  In terms of measuring the steam main..I'll assume you mean the length of the big diameter ring of pipe in the basement?  I'll also figure out what type of main vent I have.  And the pipe diameter of course.

    Thanks for the Kroil recommendation...
  • Rod
    Rod Posts: 2,067

    The big main pipe leading from the over the boiler. On the piping just give us the circumference and we can figure the pipe

    size out from that.  You mentioned 2 pipe radiators "they have a pipe

    connection on either end with no valve"   See if you can trace where

    connecting the pipes go and to what are connected. Is there a normal

    radiator vent on the these radiators?  Any sign of traps on them?  If you

    can, post some pictures of these radiators.  Where in the system are these radiators located?  Pictures of the boiler would be a help too. Take the pictures from back aways so that the piping connected to the boiler is included. If we need detail we can zoom in.

    On the radiators - Check and make sure the radiator valve on the steam pipe going into the radiator are fully open.  Also use a carpenter's bubble level and check that the radiators have a slight slope towards the steam pipe end. Just enough a bit of slope to "encourage" the condensate (water) to leave the radiator. On some old houses the floor *and radiator) has settled and now the slope is away from the intake pipe.

    - Rod
  • a3inverter
    a3inverter Member Posts: 64
    2 pipe details

    Once I get back in on Friday, I'll get the dimensions of the main

    For the 2 pipe, I'll see if I have pictures. There is a normal radiator vent on these radiators, they are of the tube (not column) type and I believe the brand is H&L.  There are no obvious traps on these "2-pipe" radiators.

    The "2-pipe" radiators are located in several places.  In the top floor hallway, in some of the bedrooms.  The piping to them is simply an elbow that comes out of the floor and into the radiator...then another elbow from the other end that then goes into the floor.  No valve at all.

    Slope of all the radiators is OK.  The main could use a few more hangers as some of the originals appear to have been replaced with rope...or perhaps they were using rope originally.
  • a3inverter
    a3inverter Member Posts: 64
    edited October 2012

    OK - updates on measurements..

    The main is roughly 101 feet long and is 2" pipe (under 8" in circumference)

    The main vent is a Dole 3C.

    I have attached a pdf showing the layout.

    Do I have enough main venting?

    *** Note:  The Dole 3c in the diagram marks the end of the return  - I forgot to put arrows on the diagram to show the direction of the steam flow ***

    In terms of the "two-pipe" radiators, there are no traps and no valves going to either end of the radiators themselves.  Each has a vent.  For the one-pipe radiators in the system, none of them have a valve, but do have vents.  The only radiator in the entire system that has a valve is the one Sunray in the upstairs bath.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Main vents

    If it were my system, I would put on 3 gorton #2's, and a low pressure gauge (0-3 psi , gauge store.com) older boilers have a larger steam chest which must also be vented through the mains, and the gauge will show you how close you are to zero resistance (back-pressure).

    With your single long pipe supplying all the radiators, you want to fill it with steam at low resistance before the steam starts to rise into the radiators. That way, all the radiators fill with steam at the same time, making the heat mor even. The radiator vents should be slower, Hoffman 40's which you may already have. Sometimes a faster vent may be needed if the radiator is at the top of a 40 foot riser, but generally the mains should be quickly vented, and the radiators more slowly.
  • a3inverter
    a3inverter Member Posts: 64
    Gauge Location

    Thanks NBC...

    What is the best location for the gauge?  Presently the boiler has none.  Is on a shared T with the pressuretrol the best location?

    In terms of measuring back-presssure, how would one go about doing that?  Am I looking for no rise in pressure as the main fills and the main vents close up?
  • crash2009
    crash2009 Member Posts: 1,484
    edited October 2012

    has told me otherwise.  I played a hunch and measured backpressure here.
  • JStar
    JStar Member Posts: 2,752

    Crash, you maniac. Love that idea! I think the idea of back pressure is the amount of pressure pushing back towards the boiler.

    What pressure does that gauge typically read during operation?
  • crash2009
    crash2009 Member Posts: 1,484
    During the venting stage,

    the antler gauge reads a little bit less than the boiler.  After the vents close, it reads about the same. I maxed out both antlers.  NBC and Gerry made me do it.  http://www.gwgillplumbingandheating.com/webapp/GetPage?pid=415  Might just be my imagination, but it feels like this max venting thing reaches right up and pulls the cold air right out of the risers.  All the radiator shut-off valves get hot about the same time. 
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    gauge location

    crash, what a great location!

    my gauge/control farm is like this. naturally a peerless 211 a has more space, but you can get some ideas.--nbc
This discussion has been closed.