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Upstairs radiators only half hot

My 1921 house was originally heated by a coal fired steam boiler. Somewhere in the past it was converted to oil and In 1978 I switched to a new Peerless oil boiler. It worked well for over 30 years and all my radiators got hot. In 2011 I switched to a Burnham gas boiler. I was unhappy with the installation as the near boiler piping was causing lots of carry-over water and water hammer. Last summer I took it upon myself to re-pipe a nice drop header following Dan's wonderful steam books. It turned out great. My steam is dry and my boiler runs quietly for a lot less time than before. Unfortunately now my upstairs radiators only got luke-warm, even on the coldest days. For all these years I have been using Hoffman #40 radiator air valves on every radiator in the house. The downstairs radiators are still heating well with those valves and they are the thin-tube type. The upstairs ones are the column type. I switched the air valves on the upstairs radiators to the Maid-O-Mist model that has the interchangeable orifices. Looking at that great chart of Gerry and Steve's in Dan's Greening Steam book I found that the #4 orifice was smaller than the Hoffman #40. The #5 was the next bigger and I tried it first. It did the trick, and the #6 was even faster. Those let the steam in much quicker and the radiators were hot again. But the top half of the radiators got nice and hot , while the bottoms stayed cool. That was acceptable, but the problem is that the hole for the air vent was about 3/4 of the way down the side. That part was staying cool so the vents never closed. Because of that the system lost all of it's pressure out the open air vents, and yet, the radiators never got completely hot. The #6 was the worst at this. The #5 was not as bad, but still lost pressure. So I went back to Dan's books to figure this out. I can only surmise that in the days of coal, the radiators had lots of time to vent completely and get hot all over. Even the oil cycle was long enough. The gas firing cycle is just too short to accomplish this. What I did was to experiment with different locations for the vent hole. It turned out that by placing the air vent all the way up at the top, it got hot enough to close. No matter where the vent was, the radiator still was very hot at the top, and cool at the bottom. But at least now the radiator tops get nice and hot and the rooms are warm. Finally I settled on the #5 orifice as the best balance between the downstairs and upstairs radiators. I feel like it was a band-aid fix, but I'm not going back to oil or coal. So was this problem caused by the column style radiators designed for coal fired steam? Is it normal for the lower half to stay so cool? Or is there another reason?


  • Fred
    Fred Member Posts: 8,541
    edited January 2018
    Typically when the top or bottom of a radiator gets hot and the other half stay cold it's because the vent on that radiator is too fast and it is allowing the steam to race across the radiator and close the vent. You seem to be saying the vent stays open. Are you sure of that? Is the vent possibly closing and only opening at the end of a boiler cycle to let air back in the system?
    Try a smaller vent. Radiators don't care what type of fuel the boiler runs on. It's the steam that does the work, on the radiator end. AND before you keep messing with radiator vents, make sure you have good Main vents on the system. If you don't have main vents or small ones, steam spends most of its time, during a heating cycle try to push air out of the mains. Is the second floor on a separate main? I'm betting main venting is a big part of the issue and venting the radiators too fast may be a secondary issue.
    EDIT: I might add, moving the vents to the top of the radiators will also cause them to close before all the air can get out of the radiator. Move them back to their original location!
  • BobC
    BobC Member Posts: 5,411
    I would also clock the gas meter to make sure the boiler is using the correct amount of steam. When firing the boiler should use the amount of gas indicated on the boilers label.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Jackmartin
    Jackmartin Member Posts: 196
    Good thoughts by everyone my thought is what are you running your steam pressure at you have to run a single pipe system the way the dead men designed it .5 on 2 psig off. Never let the system go to 0 psig. Coal fired systems NEVER went to 0. The idea about main vents should be looked into and the comment on rad venting is definitely something to think about, but you are ignoring one of Dan’s laws you always use the same venters on the whole system .Unfortunately,it has been my experience with Maid of Mist vents —— well let’s just say you stick with Hoffman. All the best Jack
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    Many of these coals systems were oversized for vapor vacuum. You really need to vent the heck out of these huge headers. The slow the radiator vents way down.

    Here’s what’s counterintuitive. But if you vent too fast, pressure goes up because radiators don’t heat completely and emit less heat. He system gets wild and unbalanced.

    Try Using the 4s as a starting point. Hoffman’s 40s are between a 4 and a 5. Is only use a 6 on a really big radiator.

    Hoffman 1A and the adjustable ventrites work great.
  • Oldslowandugly
    Oldslowandugly Member Posts: 37
    Thanks for the comments. When I mentioned the fuel I was really referring to the time that said fuel was firing and the type system (coal) in place. Coal burns for hours, giving the system loads of time to totally vent. I'm pretty sure the original boiler and radiators worked harmoniously for decades. The oil boiler also fired for a decent amount of time. All the radiators got hot. It is the gas boiler that gets up a head of steam really fast and shuts down before all the radiators are hot. So I have two mains and each feed both floors with a separate riser for every radiator. The old setup only had single main vents situated at the end of the two dry returns just before dropping down to the boiler. I added double vents at the ends of each main right after the last take off. Both sets of main vents close within seconds of each other. I used Dan's book to calculate the volume of air in the mains and sized the main vents accordingly. So the mains are venting fast, and the first floor radiators get hot first, presumably since they are closest the mains. I had the slow Hoffman #40 vents on all the radiators. With those the upstairs radiators barely got warm before the boiler shut off. Since the slightly faster Maid-O-Mist #5 air vents got the upstairs radiators hot, why would slower vents work better? Also, when the vents where down low, no, they never closed. They were cool to the touch. They were not breathing back in. I suspected that also and I used a candle to test- air vented out until the system was empty. The downstairs radiators also are cooler at the bottom, but not as cool as the upstairs ones. And even though the vents are down low they close as they should. But they are thin tube type radiators and upstairs are column type. Different characteristics?
  • Fred
    Fred Member Posts: 8,541
    It's still a venting issue at the radiators. They are venting too fast. If the venting on the radiators was correct, the radiators might not get completely hot from side to side but each section, that is hot, would be hot from top to bottom. As to why the vents aren't closing; because they close on temperature. If the steam doesn't get to them, they won't close. With the bottom half cold, the steam is likely condensing somewhere in the radiator before it can actually get steam temps to the vent to close it. The vent doesn't care if it's a tube or column type radiator. It just needs steam to close it. I will say the column type rads have more air in them that needs to be expelled.
    The other questions that need to be asked are:
    - Is the thermostat in a room that is warmer than the rest of the house or is the thermostat near a radiator where it is satisfied before the rest of the house gets up to temp?
    - Is this a programmable thermostat? Is it programmed for steam heat (1 or 2 cycles per hour)? They come from the factory with a default setting for forced air, with a setting of five cycles per hour. Check your manual for the thermostat and make sure you are programmed properly.
    - Are your mains insulated? If not, it is possible that the steam is condensing before it gets to the radiators.
    - What vents do you have on each main? Is one main larger/longer than the other? Steam will take the path of least resistance. You can't balance radiators until you have the main venting correct.
  • Paul48
    Paul48 Member Posts: 4,469
    I'd clock the meter, as said. It sounds as though you are not producing enough steam. A difference in pressure moves the steam. You aren't creating that difference. The steam you are producing, is condensing faster than you are making it, or the open vent would be blowing steam.
  • Oldslowandugly
    Oldslowandugly Member Posts: 37
    " the radiators might not get completely hot from side to side but each section, that is hot, would be hot from top to bottom." Exactly. None are hot from top to bottom except the first section which is right off the inlet pipe. Only the tops get hot- very hot in fact. So if the steam is condensing and keeping the bottom cold, and the air valves not closing, isn't it odd that it is only occurring on all of the column radiators? The thermostat is in a big hard-to-heat room, so, no, it is not getting satisfied prematurely. The thermostat is the old style round Honeywell with the mercury switch inside (foolproof IMHO). The anticipator is set all the way at the end on the steam setting. Mains are 2" and insulated. Dry returns are not, as I need some heat down there. Mains have two each Maid-o-Mist #1 main vents on a 3/4" stand-off manifold after the last take-off. The older-than-me Dole Quick Vents are still at the boiler ends of the mains and still working. All main vents close within seconds of each other. Both mains are exactly the same length, a credit to the Dead Men installers. I spent a lot of time on the main venting and I am confident it is as good as can be. Here's what I can do. As a test I will put the #4 orifices on the upstairs vents. Then they will be slower than the downstairs #40's. I know the Maid-o-Mist have a bad reputation. I used them because of the interchangeable tips. I planned on using them to fine tune the system, then replace them with corresponding size Gortons as they failed. None have failed yet. Stay tuned.
  • Oldslowandugly
    Oldslowandugly Member Posts: 37
    PS- Jack- my pressure is .5 to 1.5. I am a believer in low pressure too. I was using the #40's on all radiators until this issue popped up.
  • Paul48
    Paul48 Member Posts: 4,469
    Boston area?
  • Fred
    Fred Member Posts: 8,541
    How old is the boiler? Have you measured your total Radiator EDR and compared that to the Sq. Ft. Steam rating on the boiler plate? If the boiler is sized properly (not too small) I have to believe you may not be getting enough gas to the boiler. As has been said, clock the gas meter.
  • Paul_11
    Paul_11 Member Posts: 210
    oldslowandugly, I read all of your posts and I never got a sense of what is the actual problem you are having keeping your home comfortable to live in. If you are comfortable, what is the problem. I would not care if a radiator does not heat up completely if the air temp was comfortable.
    I would care if the room was not comfortable.
    It seems like you have a two story home.
    1) Are you cold on the second floor?
    2) What are the air temps up and down?
    3) You are trying to balance your steam distribution at the radiators , which is not ideal as the best way is "Master venting". Using the radiator vents to balance sometimes works in smaller single family homes but not in larger single family and never in multiple dwellings.
    You never answered the question about master venting. Did you put master vents at the top of all steam risers on the steam supply pipes? That may just be the best way to balance your home.
    4) If any rooms end up hotter than others, just add TRV. They work great when you are operating at 1psi or less.
    5) what is the make and model of the old oil boiler and the new gas boiler?
    Since 1990, I have made steam systems quiet, comfortable, and efficient. We provide comfort while saving the planet.

    NYC LMP: 1307
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    You need to start with #4 on the downstairs radiators. They are too fast. Then use the 40's upstairs. They have long risers, so there's more air volume to vent, even if the radiators are a little smaller.

    If some upstairs are still cold, use the 5's. A Hoffman 40 vents about like a 4.5... or maybe 4.75. just a little slower than a 5, but a lot faster than a 4.

    If radiators near the start of the main heat up a lot faster with the same vent size, you probably still need more main venting.

    Keep in mind too that the run outs or laterals to the radiators near the start are shorter because the main is located closer to the ceiling. Later radiators have longer runs.

    The good dead men however, realized this, and they normally ran the main towards the norther east corner of the house first, then ran clockwise from there. This is the more shaded parts of the house.

    Balancing isn't easy. Some radiators are just stubborn or maybe there's poor consistency in some radiators vent performance. I'm still struggling with one of these very long, but short radiators with steam racing across the top. I think the simple truth, is that the boiler is oversized for the EDR, and theres some issues i can;t get around.
  • steamedchicago
    steamedchicago Member Posts: 72

    That was acceptable, but the problem is that the hole for the air vent was about 3/4 of the way down the side.

    The vents are located towards the bottom of the radiator because steam is less dense than air, so the top of the radiator fills with steam before the bottom. If the vent is at the top, the steam hits it and closes it before air is all forced out.
  • Oldslowandugly
    Oldslowandugly Member Posts: 37
    OK, I'll answer in order. New York City. Boiler is 2011, and slightly oversized. The gas meter shows the boiler runs properly. And the problem was cold radiators upstairs. But I could not address that until I straightened out the near boiler piping. It is a medium size two story home. I did not go the extra yard by adding main vents at the tops of the risers. While that is the best way, I am old so I try the easy stuff first. Thus I used faster air vents and they worked well to heat the second floor properly. Long gone oil burner was a Peerless 5 section, gas is a Burnham Indepedence 5 section SIN5LNI-LE2. That's an idea, #40's upstairs and #4's downstairs, same principal. But here is what I did. I put the #4's on two of the upstairs radiators. I left the #5's on the other two. It's really Winter again so I was able to judge quickly. What I got was two hot radiators that the vents closed and those were the #5's. The other two got lukewarm and the vents never closed. Those were the #4's. So while I watched with a borrowed cigarette making smoke, the #4's vented until the system was empty. BUT, then they paused, and then began to suck in on vacuum. I did not notice that before because the change was imperceptible without smoke to expose it. So, they never closed at all. The #5's got hot, closed and opened properly, and did not suck air in on shutdown. I put them back on the two cool radiators. I am happy with the upstairs heat now and the vents being up high does not bother me, I just wanted to know why that worked better than them being down low . The thermostat is set at 65°, the downstairs thermometer is showing 65° and the upstairs is showing 64°. I can't complain about that. Thanks to all for the responses!