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Gas fired Steam Boiler replacement questions

Hello. I currently have an old Thatcher boiler which starting leaking. I hired a cast iron welder to weld the part, but was unsuccessful-- still leaking. Rather than repair we opted to replace with another compatible steam boiler. If you are familiar with Thatcher, it has a millivolt system which operates the system without the assistance of electric, a feature which I am not willing to live without. The newer system is a steam boiler with the millivolt and 280 btu. My concern is the compatibility with my current system of 180 btu. My home is 2300 square feet and I have 11 registers/radiators. Pipes are 1.25" diameter. Can the system be adjusted to fit my home? and will entire pipe system need to be replaced?
Thank you.


  • The boiler capacity seems several sizes too big, based on square footage, so do a search for sizing a steam boiler here, or "EDR".
    You should really find a good steam pro to make this replacement. Use the find a contractor button here, or if you are considering someone already, ask for pictures of his work.--NBC
  • KC_JonesKC_Jones Posts: 4,093Member
    You need to size the boiler to the connected load. I am assuming you are talking about installing a used boiler because it has the millivolt system?

    What is your issue with a new boiler that doesn't have a millivolt system?

    Unless you add up the radiator EDR you don't even know if the current boiler is the proper size, but if it is you are talking about going much larger which would make you massively over sized which would be quite bad.

    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • vintagefurnacevintagefurnace Posts: 14Member
    I have a gas steam boiler with millivolt system. The problem with the unit is that the fire box is leaking in the rear of the unit. can the firebox be replaced or welded? If not, what compatible system with millivolt ignite system of good quality can you recommend? My boiler has a 180k btu capacity.
    Thank you.
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,618Member
    As far as I know millivolt is not allowed on new boilers. It's use is limited to gas fireplaces I think.

    The new code require two gas valves or 1 double seated valve. Millivolt doesn't have enough power to operate 2 valves
  • nicholas bonham-carternicholas bonham-carter Posts: 7,817Member
    I believe that some boilers are supplied with a millivolt gas valve for use in Amish communities, and maybe someone else here may have some more concise information on where to find one.
    Do not just replace your current boiler with another one of identical capacity, as it may be too big. The radiators must be measured to determine the necessary EDR (measured in square feet of steam). It’s not hard to make those measurements yourself.
    The new boiler will have to be piped in accordance with the manufacturer’s instructions, or it will not work properly.—NBC
  • clammyclammy Posts: 2,211Member
    I haven’t seen a millivolt being purchased or installed in many years and I know in my area u can not get a standing pilot they are not made and ain t available ,I did one was few months back but that was only because my buddy had it ear marked at the supply house for about a year or so due to knowing he needed it for some one . I guess if your he’ll bent on millivolt you would just get a new pilot assembly gas valve and generator and have some one do it for you . In the past I ve replaced a few old thatchers and usually as a note I seen repairs to old cast attempted to be repaired on those oldies by guys who where excellent welders of garbage and in about all cases it failed in short order. I think u should re check you edr of your system , then do a heat lose to allow for any insulation upgrades that may have been done windows door and last but not least at few simple question . How well did the old boiler heat your home ? If you say good that means all rads hot even temperature able to recover from a thermostat set back ? Does the boiler short cycle or does it run straight out till the thermostat is satisfied ? If all that equals yes I think I would go clock my gas meter and figure out what your using .i would think that between clocking your meter and edr will bring you to the correct sized boiler.One small note remember and mark the height of your old boilers water level and do some reading up on gravity reservoir tanks and have your installed leave a extra tee on the supply header and return side of the boiler .Weil McLean has some literure some where on there site .reason I say this is those old style boilers held a lot of water and had a a lot more surface area the modern boiler equaling to longer run times before cycling on low water . That reservoir tank is the cheapest alternative remendy I know of . Best of luck and make sure the guy spinning that wrench knows exactly what’s he’s doing .peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • vintagefurnacevintagefurnace Posts: 14Member
    Thank you, Clammy for your response and advice.
  • Inliner311Inliner311 Posts: 25Member
    I understand the appeal of a millivolt system. We had one before we had our current boiler system. You probably won't get a new system and I wonder if a company would even warranty it if you were able to find one.

    A new system will most likely save you money on your gas bill. We went from a converted coal millivolt boiler to one with about 80% efficiency and our gas bill was cut in half. It also starts producing steam alot quicker.

    If you go the used route, you have all the millivolt components so you don't technically have to find a used millivolt boiler. You just have to find one that matches your boiler size and doesn't have any addition components that your millivolt has. It will most likely be alot of work to get it working properly and need someone that knows millivolt systems well.

    I personally would go with a new system for cost savings in fuel then find a backup system for power outages.

    What components does your boiler have? Like does it have a vent dampers, low water cutoff, automatic water feeder, etc
  • Jamie HallJamie Hall Posts: 10,274Member
    There is simply no way, unless you have made extensive additions to your house, that the 280,000 BTUh boiler you are considering is going to be the right one, considering that you currently have a rather inefficient 180,000 BTUh boiler. It will be at least two times as big as it needs to be -- probably more -- and be difficult to control and run -- and a gas hog.

    The folks above are correct. Step one is to find out the EDR rating of your current radiation. "EDR" is the equivalent direct radiation, and is a measure of how much steam can be condensed. You want to match that number as closely as you can with the EDR rating of the new boiler -- that rating is a measure of how much steam it can produce.

    Bigger is not better with heating systems.

    You are going to be very limited in finding a new -- or even recent used -- gas boiler with millivolt controls, if you can find one at all.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • vintagefurnacevintagefurnace Posts: 14Member
    Thank you for your comments and advice. Can anyone advise of a quality brand that is well constructed ? My Thatcher has lasted a score of over 50 years, because it was simply made to last, unlike today, considering it fortunate to acquire a unit with a 10 year warranty. Regulations were changed for energy efficiency, but what about the damage incurred from wasteful refuse of limited use systems, not to mention the recurring cost to the consumer?
  • Jamie HallJamie Hall Posts: 10,274Member
    The length of the warranty is an exceedingly poor measure of the quality of a boiler -- nor is it useful gauge as to how long a boiler will last in service. There are many factors involved in longevity -- foremost among which are a quality installation and faithful maintenance.

    That said, there are at least half a dozen very regarded boiler manufacturers. The most important factor is not the label on the boiler, but the quality and ability of the installer -- and it helps a lot if the installer is familiar with and likes the particular boiler.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • vintagefurnacevintagefurnace Posts: 14Member
    Thank you. I have been advised that the quality of the installer is the key. Can you recommend anyone?
  • Jamie HallJamie Hall Posts: 10,274Member
    Sort of depends on where you are... so the question is, where is this job?

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • SeanBeansSeanBeans Posts: 291Member
    Please say Denver!
  • vintagefurnacevintagefurnace Posts: 14Member
    I wish. I am in New Jersey.
  • SeanBeansSeanBeans Posts: 291Member
    Me too, originally :).

    Call @EzzyT or @Dave0176
  • EzzyTEzzyT Posts: 811Member
    @vintagefurnace you can reach me at 201-887-8856.
  • FredFred Posts: 7,813Member
    @vintagefurnace , These are Two great options!
  • SteamheadSteamhead Posts: 12,868Member
    Fred said:

    @vintagefurnace , These are Two great options!

    Agreed. You can't go wrong either way.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
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