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replacing coal fired steam boiler

SethYank Member Posts: 13
I am quoting to relace a Crane coal fired then converted to natural gas steam boiler. It is a 2 pipe system, no traps, boiler centered in basement, with one main forward and one main back. No air vents on the mains or the radiators, only one vent in basement high on the return lines, could not get close to it but am assuming it was the original vacuum air vent. Replacing this boiler with a modern natural gas I need air vents on the mains and should I vent the radiators and keep or eliminate the return vent. the other item I am thinking about is putting thermostatic regulating valves on the radiators, there are 7 radiators, two story with the tstat on first floor close to boiler. Advice would be appreciated I am trying to learn to do these right.


  • Jamie Hall
    Jamie Hall Member Posts: 21,111
    Try to find out if this was originally a vapour or vapour vacuum system and, if so, what kind -- there were several. It probably was. A photo or description of one of the radiator valves could be very helpful! These systems operated on very low pressure -- ounces per square inch -- and many of them either had orifices or calibrated valves on the radiators, which may -- if you are lucky -- still be there. Those don't need traps.

    What they do need is the air vent on the dry return, near the boiler.

    You will need to keep the main air vent on the return near the boiler or, more likely, replace it with something bigger.

    Do NOT, repeat NOT, put vents on the radiators.

    Depending on the exact type of system, air vents on the mains will help. On some systems, however, they will most assuredly NOT help and even can prevent the system from operating properly. Be careful to really find out what you have before you install them.

    I myself am not particularly keen on TRVs. While they may be useful in the odd situation where a space is seriously over-radiated and the valve cannot be closed enough to control the problem, their main effect -- particularly on a vapour system -- is to cause the boiler to short cycle since when they close it is seriously oversized. I'd avoid them.

    If the thermostat is so located as to shut off the system before some of the spaces are warm enough, consider moving the thermostat.

    You will need to control the boiler with a vaporstat, 0 to 16 ounce. Don't even think of using a pressurestat.

    Be very sure to get your boiler sizing right.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SethYank
    SethYank Member Posts: 13
    So if I am planning to go back in with a Utica gas fired boiler I should still treat it as a vopor system. I was thinking that the new gas firing system is much faster than the old coal and the need to get the air out of the piping and radiators was necessary . the radiators currently have the old regulating T handle valves on them but are in poor condition that is why I was thinking about trv's but could go back in with regular flow control hand wheel valves
  • KC_Jones
    KC_Jones Member Posts: 5,409
    You probably will need to get the air out much faster, but you need to do it on the return lines NOT at the radiators. This is a 2 pipe system and the air us pushed out through the return lines not out through the radiators.
    To quote Jamie: "You will need to keep the main air vent on the return near the boiler or, more likely, replace it with something bigger."
    I will also reiterate make sure you add up all the EDR in the house and size the boiler properly, too big will wreak havoc with tuning the system properly and waste fuel. Do you have Dan's books? If not I highly recommend you order up at least the Lost Art, great book with tons of information. Question, why are you assuming all the valves need replaced?
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • SethYank
    SethYank Member Posts: 13
    Little bit of an assumption, the house is in an older section probably early 1920 was used as a rental now owner occupied. my experience is these valves have been abused and leak. Was hard to test the system was cold.
  • SethYank
    SethYank Member Posts: 13
    I have Dans books and read them just looking for some quick response help for this quote since I am slammed with cooling season. I just read his article the other month about coal systems and realized I need to put some thought into this change out and not just slam a boiler in. I have measured all the radiators and am in the process of sizing.
  • Jamie Hall
    Jamie Hall Member Posts: 21,111
    Seth -- the valves may well leak, but around the packings. It is possible that they may leak internally, but not all that likely -- and it is no big deal to replace the packings (usually... !). A lot easier than replacing the valves! And if you keep the pressure where it belongs...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • vaporvac
    vaporvac Member Posts: 1,520
    This definitely sounds like a vapor system and probably an old vapor vacuum one given the single venting mechanism. In fact, you could be describing my Trane VaporVacuum system, although there were others that worked in a similar fashion. The venting is on the returns, rather than the mains.

    Two-pipe systems don't need vents on the rads. As jamie mentioned, the vapor systems had special graduated valves that worked extremely well at mitering the steam flow. If not, they had inlet orifices. These systems NEED to run at very low pressure: in ounces, not pounds. Also be sure the waterline of the new boiler matches that of the old.
    What is the edr of this system? It could benefit from a two-stage burner. That's the best was to simulate a coal fire. My twinned system works on the same concept and delivers very comfortable, efficient heat. PLEASE post some pics of the central vent in the basement and a representative radiator.

    I would encourage you to keep the vacuum working, especially if you opt for a two-stage burner. Once the air is expelled, the heat delivery is quick and long lasting. With a good edr match,, it should expel all the air and may keep the vacuum til the next cycle, thus heating at a slightly water temp. They still sell vacuum vents.
    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
  • Steamhead
    Steamhead Member Posts: 15,993
    Do those original radiator valves have names or trademarks on them?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service