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Steam Radiator only heating halfway

We have a home built in 1920 with original boiler (converted to gas) and radiators.  It is a two-pipe (in=at top, out=at bottom) system but does not have traps on the radiators (as far as I can tell, they're just simply return pipes) and obviously since it's two-pipe, there are not valves on the individual radiators.

Of the 9 radiators, only 2 heat completely.  The rest get hot at the top 1/3-1/2 but do not get hot at all on the bottom.  One of them is shorter and longer and gets hot by the intake but stays cole by the return pipe.

Is this at all normal?  The house gets to the temp set on the thermostat, but I'm assuming this issue makes the system overall inefficient.  If I don't have traps, what could the problem be? 

I do blow out the boiler weekly during the winter and monthly when not in use.


  • Rod
    Rod Posts: 2,067
    Orifice System

    Hi- It sounds like you have orifices which means you either have a inlet valve that has an adjustable orifice or a orifice plate with an orifice hole. (Post a picture of you inlet valve and any numbers or letters on it and we may be able to identify it for you. The orifice size is matched to the size of the radiator so that just enough steam to supply that individual radiator enters so therefore there isn't a need for a trap to keep the steam in the radiator.

    It's normal in the spring and fall (mild seasons) that radiators don't get completely heated all the way across. In your case it may mean that the orifices need to be cleaned or replaced. New orifice plates are available from Tunstall http://www.tunstall-inc.com/tunstall-steam/inlet-orifice/

    I envy you having an 2 pipe orifice system as they are the “Cadillac” of the steam systems and can be fine tuned for ultimate comfort and efficiency.

    - Rod
  • diygirl1208
    diygirl1208 Member Posts: 3
    Additional Info

    Wow!  Thanks for the quick response!

    I didn't realize it was normal for radiators to not heat up fully in Spring/Fall.  Would there be a reason that 2 of 9 do heat up fully while the rest go only half way?

    Attached are pictures of the inlet and outlet of two different radiators--one with an old (I think original--no info on it except the hash marks for how far it's open) and one with a new one replaced a few years ago (Sterling, Inc. 01 on one side of nut, L9 on other side).

    I don't know if spurting from the old knobs (different from new in that there's a bit of a gap where it goes up and down as you turn it) or the age of the knobs has anything to do with how far it's heating up, but these are the specifics on the 9 radiators (all valves are fully open):

    Downstairs (thermostat is downstairs closest to the first two listed):

    1. Old knob, no leaks/spurts, only top half heats

    2. Old knob, slight spurt, only right (inlet side) half (long, horizontal radiator) heats

    3. Old knob, spurts quite a bit, top half only

    4. New knob, no spurts, I think it was heating fully, but a piece of plastic snapped off from handle, so it's in the half-open position now

    5. New(er) knob, no spurts, heating fully

    Upstairs (attic a/c thermostat puts it at about 3-4 degrees warmer than downstairs):

    6. Old knob, no spurting, top half only

    7. Old knob, spurts a lot, top third only

    8. Old knob, some hissing but no spurts, top third only

    9. New knob, no spurts, heats fully

    Is it recommended to ask a technician to clean or replace the orifice rather than install new knobs?

    Also, I don't know if it has anything to do with anything, but I've read that Pressuretrol should only be 2psi or less...it gets up to 3 (it's set at .5).  Is that a problem?

    Thanks for the envy! ;-)  I love the system...just have to figure out how to fine-tune it.
  • vaporvac
    vaporvac Member Posts: 1,520
    Lower that pressure!


    I have a system similar to yours. They're designed to run on Ounces of pressure, not pounds. I'd start by lowering it to 2 lbs. max with a lower cutin. This really helps even out the heats. Perhaps you could post pics of the types of valves you have along with your boiler and its piping and the experts on this site could comment.

     Mine also don't get hot all the way across in the swing seasons, especially now that I've upgraded my attic insulation and added tight interior storms and various other weatherstripping. It soulnds like yours might just need some tweaking.\You should seriously consider getting at least one of Dan's Steam books if you haven't already.  Good luck.
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
  • NewlyPuzzled
    NewlyPuzzled Member Posts: 30

    Thanks for the info.
  • Dave in QCA
    Dave in QCA Member Posts: 1,785
    New Valves Overheat

    I notice that you say that the radiators with the new valves heat all the way across.  That is because they are standard open type valves with no type of orifice built in or otherwise added.  So, on these the steam just goes roaring in.  You might be able to get these in balance with the others that are working correctly by closing the valves almost all of the way.  To do this, close the valve completely, then open it about one complete turn.  You can than increase or decrease to fine tune it.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • diygirl1208
    diygirl1208 Member Posts: 3
    Can't Lower Pressure?

    The boiler used to only go to 2psi max...the last technician to clean/inspect boiler last month replaced the Pressuretrol and gauge...since then, it goes up to 3psi.  The Pressuretrol is set at .5 ...as far as I'm aware, there's no other way to lower the pressure?

    My boiler is original from 1920...if you're ready for Big Scary Red, I'm attaching a picture.  Simple, solid system, but I don't see anywhere else that it'd be possible to adjust steam pressure other than the Pressuretrol?
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