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What Temperature Should a Steam Radiator Reach?

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I was just wondering, when steam is up in the system and an individual radiator's air vent has been satisfied, what temperature should the cast iron radiator be at?

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  • Mark N
    Mark N Member Posts: 1,115
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    All depends upon the pressure the boiler is operating at. At 1psi I believe the steam is 215 degrees.
  • FXProglJr
    FXProglJr Member Posts: 83
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    thanks and yes, I agree...but I'm asking because I have some cast iron radiators that are getting steam and their air vents are venting (if I listen closely, I can hear them vent and shut off and then vent and shut off again, etc), but the radiator itself only gets to 150*F (measured with a handy IR thermometer)
  • Mark N
    Mark N Member Posts: 1,115
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    How sure are you that you're getting an accurate reading?
  • Gordy
    Gordy Member Posts: 9,546
    edited December 2014
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    An IR thermometer can not accurately measure temps on reflective surfaces. Use a piece of frog table and shoot that. Also at what point in the call for heat are you checking temps, and where on the rad.
  • steamedchicago
    steamedchicago Member Posts: 72
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    I worked out how much filling the radiator in my bedroom with steam would raise its temperature. Just filling it once, and letting the steam condense and cool to room temperature is enough heat to raise the temperature of the radiator by about about 1/2 of a degree F. Of course, the radiator gets filled repeatedly in operation, but that's not what you asked.

    Also, remember that the point of the radiator is to heat the room. It's not to get hot. If the room is comfortable, I wouldn't worry about it much. The radiator gets filled with steam, which condenses, and gives up that heat to the radiator. The radiator transfers that heat to the room. Unless it's cold enough that the boiler runs a long time, the radiator won't get to the temperature of steam. The sections nearer the input valve will get hotter than the ones nearer the vent, and may get to steam temp when the far side is still cold. Two pipe vapor systems were set up so that the radiators never got hot except on the coldest days, because they could condense much more steam than the input valve allowed.

    I suspect you're trying to figure some problem out, but you haven't told us what it would be.
  • FXProglJr
    FXProglJr Member Posts: 83
    edited December 2014
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    yes, you are correct...I'm trying to figure out just why the 2nd floor in Grandpa's 2 story (+ basement) house consistently gets 4*-8* warmer than the first floor. I've calculated EDR's. & checked for imbalanced EDR, but the setup seems ok - 1st floor 615 sq. ft & EDR of 141 or .22/sq ft and 2nd floor 680 sq. ft & EDR of 176 or .25/sq. ft. Everything seems to be working fine, but I was surprised to see that the first floor radiators only got to around 150*

    I should mention that, even though I could hear the air vent venting on the biggest radiator in the apartment, I took the air vent off (it had quite a bit of water in it) and replaced it with a new one that had a much smaller vent hole. That radiator now gets up to 195*F. I thought I was on the right track (even though I still don't understand why), but when I tried replacing the air vent on another radiator, it still only gets to 150*.

    I'll measure the temp on the pipe right before they enter the radiators and report back as soon as I can
  • nicholas bonham-carter
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    See if you can determine whether steam gets to each floor at the same time, and tell us what main vents you have on the returns, and radiators. If you followed the diagram on the Gorton website, this sort of imbalance can happen,[great product-bad advice!].
    improper thermostat placement can lead to problems, as well.--NBC
  • FXProglJr
    FXProglJr Member Posts: 83
    edited December 2014
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    well...first...I happened to be there when a heating cycle started....so I waited with my IR thermometer until the radiator air vents stopped venting (or at least started going on and off). I measured the temp at the main shut-off valve body and at several places on each of the 1st floor radiators. All of the shut-off valve bodies were at 180* (or slightly more). The big radiator I spoke about above was at 190-195*, but all the other radiators on the first floor were only 150*. (Should I try hooking up a manual vent to one and see if I can get it to get hotter when the furnace is making steam?)

    As for the vents themselves......the furnace is in the center of the basement and there is a separate 1-1/2" main going to the front of the house and the rear of the house for each floor. Each end of each main ends in a tee with a 1" return on the bottom and a Gorton No1. on the top. All of the radiators on the 2nd floor have Maid-o-Mist air vents with #4 (small) hole. All of the radiators on the 1st floor used to have #6 (or larger), but I've now changed them to a #5.

    Oh...one more thing...the thermostat is on the 1st floor...which is what leads me to believe that I have some problem with the setup or radiators for the 1st floor
  • nicholas bonham-carter
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    the steam should hit the radiator valves all at the same time.--NBC
  • Fred
    Fred Member Posts: 8,542
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    Keep in mind that heat (of any kind) will naturally rise. Does this house have a open staicase to the second floor? They can act like a chimney and draw heat up to the second floor. Is the thermostat located near an exterior door or affected by drafts from an exterior door? Going in and out of a house frequently or leaving windows and doors open will cause the thermostat to call for heat to maintain the first floor while a Chimney effect and fewer/no exterior door opens on the second floor will retain heat better than the first floor.
    There are way too many variables during different heating cycles to try to get a consistent temperature reading on individual radiators and have it mean anything. Variables include venting rates, distance from the boiler, boiler run times, outside temperatures, radiator size, radiator type, radiator temp at start of a heating cycle, etc.
    If they have a door at the top of their stairs, close it for a couple days and see if the temp on the 2nd floor get closer to the first floor. If the temps on the second floor continue to stay much higher than thee first floor and you determine it is primarily from the radiators, maybe consider smaller vents or something like Danfoss Thermostatic Radiator valves.
  • SWEI
    SWEI Member Posts: 7,356
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    Fred said:

    Keep in mind that heat (of any kind) will naturally rise. Does this house have a open staicase to the second floor? They can act like a chimney and draw heat up to the second floor.

    Hot air and hot water both rise (due to convection.) Heat merely flows (to cold, aka less heat.)
    Canucker
  • RobG
    RobG Member Posts: 1,850
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    SWEI said:

    Fred said:

    Keep in mind that heat (of any kind) will naturally rise. Does this house have a open staicase to the second floor? They can act like a chimney and draw heat up to the second floor.

    Hot air and hot water both rise (due to convection.) Heat merely flows (to cold, aka less heat.)
    I have the same awful habit of correcting people when I hear that heat rises. It drives my wife crazy as I can never hold my tongue.
  • SWEI
    SWEI Member Posts: 7,356
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    I know the feeling (but it makes it so much easier to explain why their suspended tube system is not heating the house)...
  • Fred
    Fred Member Posts: 8,542
    edited December 2014
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    SWEI said:

    Fred said:

    Keep in mind that heat (of any kind) will naturally rise. Does this house have a open staicase to the second floor? They can act like a chimney and draw heat up to the second floor.

    Hot air and hot water both rise (due to convection.) Heat merely flows (to cold, aka less heat.)
    Firstly, it is important to know that the air all around us consists of molecules that are constantly in motion (moving). When the air begins to heat these molecules start to move faster and bump into each other. This causes more space between the molecules and the air expands to become lighter (less dense). This causes the hot air to rise. Once this hot air begins to cool it begins to move more slowly and becomes heavier again (more dense) and it slowly sinks back to the ground.

    Maybe I should have said the open staircase creates a path by which the heated air can rise but I wasn't trying to split hairs or blow hot air. (Pun Intended)

  • Gordy
    Gordy Member Posts: 9,546
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    That's convection Fred. Kurt, and Rob are merrily pointing out that you said incorrectly "heat of any kind rises" which is not the case. Radiant energy heats objects I'm sure you know, and does not rise. Air molecules coming into contact of radiantly heated surfaces become excited, and more buoyant, and convection happens, but not to the extent of say a forced air or convection type of emitter.
  • Fred
    Fred Member Posts: 8,542
    edited December 2014
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    Gordy said:

    That's convection Fred. Kurt, and Rob are merrily pointing out that you said incorrectly "heat of any kind rises" which is not the case. Radiant energy heats objects I'm sure you know, and does not rise. Air molecules coming into contact of radiantly heated surfaces become excited, and more buoyant, and convection happens, but not to the extent of say a forced air or convection type of emitter.

    You (and they) are so correct! Don't know why I said "Heat of any kind" My Bad
  • Gordy
    Gordy Member Posts: 9,546
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    I know what you meant Fred, it's just a constant battle with the general public to grasp heat transfer, and how it effects the comfort environment we try to achieve. So for the readers lurking" in the blinds...........
    Canucker
  • Jamie Hall
    Jamie Hall Member Posts: 23,280
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    Sort of going back to the beginning...

    Unless a radiator is really truly full of steam, parts of it -- sometimes lots of it! -- may be quite cool. But the area around the inlet, at least, should be right up there. If not 212, close to it.

    IR thermometers, though, are really sensitive to surface finish. Most flat paint will give a pretty close reading. Metallic paint, though, or shiny bare metal, may give readings which are way too low. Something to consider. The tape trick works pretty well, though, if it's tightly adhered.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
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    Air vents close at 140 degrees right guys? A fast vent may let some air remain in the radiator and diluting the effectiveness of the radiator.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
    https://heatinghelp.com/find-a-contractor/detail/charles-garrity-plumbing-and-heating
  • FXProglJr
    FXProglJr Member Posts: 83
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    well..I'm glad we're back on topic......

    if the air vents are supposed to close at 140*, that may be the answer to my question (but, then again, how do we explain the radiator that's making it to 195*?)

    I'm going to manually let the air out of one of the radiators that doesn't get past 150* by replacing the air valve with a short nipple and ball valve (and keep opening and closing it to make sure the radiator stays full of steam) and see if I can coax it to get up to 195*. I'll let you know how I make out

    And even with the silver paint that Grandpa put on all the radiators, my IR thermometer seems to be right in the ball park. I mean, when it says the radiator is 150* or so, I can touch it. It's hot, but not unbearable. I can't touch the radiator that reads 195*
  • steamedchicago
    steamedchicago Member Posts: 72
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    If you can hear the air leaving the radiator vent, you're likely at too high a pressure, or not enough main venting, or both.
    FXProglJr said:

    well..I'm glad we're back on topic......

    if the air vents are supposed to close at 140*, that may be the answer to my question (but, then again, how do we explain the radiator that's making it to 195*?)

    I'm going to manually let the air out of one of the radiators that doesn't get past 150* by replacing the air valve with a short nipple and ball valve (and keep opening and closing it to make sure the radiator stays full of steam) and see if I can coax it to get up to 195*. I'll let you know how I make out

    I've never checked the operating temperature of an air vent, but 140 seems low. Also, you shouldn't need to open the valve; close it once you've got steam coming out, and it'll behave like a regular valve. A given volume of steam will condense into 1/1600 that volume of water. (In units that might make sense: 1 teaspoon of water will make two gallons of steam!) The condensing of the steam creates a vacuum that pulls steam into the radiator, which condenses, and creates vacuum that pulls steam...

    I expect your second floor too hot problem is a combination of lower heat loss up there (Is the attic insulated? It probably wasn't when the house was built, which would drastically change the heat loss from what the builder expected. So would new better sealed windows.), plus the tendency for heated air to rise, and imbalanced venting. You may have a steam distribution problem, which the fact you can hear the air escaping from the valve suggests. Are the main vents working? Will they make a piece of paper flutter when the cycle starts? (do no use a hand you wish to keep to check for steam.) If the vents for first floor are stuck shut, the steam to the radiators on that floor will be delayed, and the top floor will get more steam.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
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    180 is the temp it closes at if it is an alcohol diaphragm style. Bimetalic ones can be lower.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
    https://heatinghelp.com/find-a-contractor/detail/charles-garrity-plumbing-and-heating
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
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    Boilers being under sized or under fired can cause low temperatures at radiators as there is not enough steam to go around. Have we confirmed fire rate to system load?
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
    https://heatinghelp.com/find-a-contractor/detail/charles-garrity-plumbing-and-heating
  • FXProglJr
    FXProglJr Member Posts: 83
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    Initially, I didn't post the ultimate problem I'm trying to solve because the question at hand was why some radiators only reach 150* . I'll respond to the other suggestions in the next post, but for now I'll stick to my initial question.

    I just returned form Grandpa's house where I played with 2 of the radiators that were only reaching 150*. On one, I replaced the Maid-O-Mist air valve with a nipple, elbow and small ball valve. When the furnace fired up, I manually made sure the radiator kept full of steam and sure enough, that radiator made it to 190*! On the second radiator, I removed the angle Maid-O-Mist air valve and replaced it with a nipple, elbow and DURST straight air valve. That radiator made it to 170*.

    So...it seems I have a venting problem. This section of main is about 30' of 1-1/2" pipe with 4 radiators on it and the main vent is 1 Gorton #1. Sometime in the next few days, I'll add some venting to that section of main and report back
  • BobC
    BobC Member Posts: 5,477
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    Go over the 1-1/2" main and the leader that feeds this radiator and make sure it all has good slope. Also make sure there are no dips in the piping that might pool water.

    What is the EDR of the 4 radiators on the 1-1/2" main? Is this main a counterflow main?

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • FXProglJr
    FXProglJr Member Posts: 83
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    Now I'll respond to some of the other comments;

    First, I'd like to thank everyone for their help. I'm still a novice at this and you are providing some suggestions I hadn't thought about.

    I can only hear the air leaving the radiator vent if I put a short piece of hose up to the vent and the other end to my ear. My furnace reaches 1.7# pressure max (I need to work on the pressuretrol to get it lower - or replace it - but thanks to suggestions from this site, it's much lower now that it's been in the past.)

    This is a 2 family house (+ a basement) with one apartment on each floor. Tenants keep their apartment doors closed, so there is no free air movement to the upstairs apartment.

    The thermostat is on an inside wall and not subject to drafts

    Yes, the 2nd floor has less heat loss than the first floor because I recently replaced the windows with the current standard double glazed, sealed, low e, etc. window. The first floor had the windows replaced about 20 years ago with double glazed whatever was state of the art then windows. And there is a surprising difference - see attached. (But that's a separate discussion from why 1st floor radiators were only reaching 150*)

    I believe my furnace is, if anything, oversized. It's rated for 471 sq.ft of steam and the total connected radiator EDR is 319.
  • FXProglJr
    FXProglJr Member Posts: 83
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    Bob...thanks for your ideas.

    the 4 radiators on the section of 1-1/2" main have a total EDR of 90.3. (and I have no idea if how many/much should be on a main of that size)

    I'm not sure what you mean by "counterflow" but the main slopes downward after leaving the header and there is a tee in the end with the Gorton #1 on top and a 1" condensate return on the bottom. The return slopes down as it heads back to the furnace.

    I haven removed all the old insulation from the mains (abestos), but it seems that they slope properly and do not have any dips.

    The radiator that I manually vented started banging a few years ago, but I raised it up a bit and that problem went away.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
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    so there is a water pocket on that radiator, or at least there was before you lifted it. with the vent removed and the steam hitting it faster it became noticeable. I stated before that venting a radiator too fast can leave behind an air pocket. What style of radiator are we dealing with? So i do not put my foot in my mouth. Is it connected across the top and bottom or only the bottom?
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
    https://heatinghelp.com/find-a-contractor/detail/charles-garrity-plumbing-and-heating
  • FXProglJr
    FXProglJr Member Posts: 83
    edited December 2014
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    Here's a picture of the type radiator throughout the house. I raised it several years ago
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
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    So that type of radiator if you vent it too fast the steam crosses the top and closes the vent prematurely. Vent the mains FAST and the radiators moderately.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
    https://heatinghelp.com/find-a-contractor/detail/charles-garrity-plumbing-and-heating
  • BobC
    BobC Member Posts: 5,477
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    If that 1-1/2" main slopes down and has a return on it it is a parallel flow main (Steam and condensate flow in the same direction). My tables only go down to 2" but an EDR of 90 should be ok as long as the slope is good and there are no dips.

    Do you know if the steam arrives at the ends of both mains at about the same time? You might need more venting on a slow main to balance things out. Adding a second #1 vent on the slow main might be helpful.

    Does the thermostat see that large hot radiator? If it's in the same room you might need a thermostatic air valve that can throttle that radiator back before it's heat hits the thermostat.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • FXProglJr
    FXProglJr Member Posts: 83
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    ok.....I've tried different size vents on the radiators and it doesn't seem to make any difference.

    There are essentially four - 1-1/2"mains - each end of each main has a Gorton #1. The furnace is in the center of the basement. 1 riser from the header splits...part to the front of the 1st floor (1 big radiator - 50 EDR - and this is the one I've managed to get to 195* regularly) and the other part to the rear (4 radiators - 90 EDR). As suggested, sometime in the next few days I'm going to get an additional Gorton #1 on this end and let you know if this helps. The second floor has essentially the same setup except 2 radiators in the front (60 EDR) and 4 radiators in the rear (115 EDR).

    The big, hot radiator on the 1st floor is not in the room with the thermostat (also on the 1st floor), but I wouldn't worry about it shutting the furnace down early....remember I started looking at this house because the 2nd floor was consistently around 78* when the 1st floor tenant was cold (at around 71*) and I can't see the new windows or anything else that would account for such a large difference (other that finding that the 1st floor radiators only got to 150* and, I'm assuming that the 2nd floor radiators get to 190 just like my (essentially the same) house just up the street.