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Boiler Replacement Questions

garrettgjp Member Posts: 26
Hey all,

My 22 year old natural gas WM EG-35 Steam boiler sprung a leak here in ND on my 2 pipe steam system. I contacted my local contractor who has worked on my system before to work on ordering a replacement. The near boiler piping is not up to par with what I see here at heating help ( my boiler has a single header, copper piping, etc) so that was a concern and made me wonder if my boiler was sized appropriately for my system.

I printed off the WM boiler sizing guide and followed the instructions. I measured my tube radiators height and width, counted the tubes and sections, calculated the EDR, BTUs/hr and came up with 98,000 BTUs/hr.

I looked at the WM EG boiler technical data under the Net Steam MBH column and it looks like the appropriate size boiler for my system is between the EG-45 (94 MBH) and EG-50 (109 MBH). Am I calculating this correctly? Should I size down when talking to the contractor?

It seems from what I read on the forum there are many more issues with oversized rather than undersized boilers. I just want to make sure when I have this thing replaced it is correctly sized for my system.

At times it seems like my boiler was running constantly to heat my house and and I never really registered any pressure on my 0-3psi gauge... was my boiler under sized? Is that possibly why this boiler had a shorter life span? The system was definitely neglected when I bought the home, so I wasn't surprised it kicked the bucket - hormel chili-esqe water drained out of the boiler the first time i tried flushing it and there wasn't a skim port on it until I added it (not pictured).

I'd appreciate any insights and input so I can intelligently discuss this with the contractor. I am very thankful for this forum for those who contribute, I have learned so much over the last few years with my steam system!!!


  • nicholas bonham-carter
    You will need more main venting.--NBC
  • Jamie Hall
    Jamie Hall Member Posts: 23,439
    The best way to size these things is to compare the EDR ratings, not the net BTUh. It's easier, for one thing... it may well be that the existing boiler is undersized. That happens. But if it's heating the house OK, that's what really counts.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ethicalpaul
    ethicalpaul Member Posts: 5,735
    Or it’s been leaking steam for a long time?
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • nde
    nde Member Posts: 86
    edited December 2019
    Sounds like you sized the new options right if the calculations are correct, I would do a EDR on the rads to confirm you must be about 400 net steam sq ft? Your piping looks all insulated which means you can probably get by slightly under but the current 35 is too small if you did the calculations right.

    20+ years is about avg for steam boiler life, if you keep perfect PH on water and do not add much make up at all then 25 or 30 is doable. People see boilers rot out in under 15 in areas of high chloride or lots of added water (leaks in system usually). Having a meter on the new boiler that tracks gallons of added water will help you know if leak exists unless you tear off all the insulation to inspect piping. The staining on some insulation does suggest some leaks. That copper header will reduce boiler life, make sure the replacement is piped in black pipe as per the eg manual, print it out if necessary to show contractor and get in writing in contract that it will be done in black pipe as per manual. It will cost more than copper which is easier and quicker which is why many contractors will do in copper.
  • garrettgjp
    garrettgjp Member Posts: 26
    Sorry the pics are a little old from a previous post here about my venting issues- thankfully those have been addressed, a contractor installed 4 big mouth vents that have drastically improved the systems functioning and the vent above the boiler no longer leaks!

    I would say the house heats ok, the 2nd floor is an apartment and some of my tenants have complained that the bedrooms are cold (the rooms furthest from the boiler) - the rooms on the main floor (where I live) have been comfortable.
    EBEBRATT-Ed Member Posts: 15,622
    As @Jamie Hall said add up the radiation that is installed (In EDR) and buy a boiler that has that EDR rating or slightly higher.

    No need to do any other math. The piping and pickup factor is already figured in by the boiler mfg.
  • garrettgjp
    garrettgjp Member Posts: 26
    @nde Yes I came up with 408 net steam Sq ft.

    Thank you for the insight. It is nice to know I got close to the normal life out of the boiler. Any recommendations on meters/automatic water feeders? I'll definitely monitor the PH to try to extend the life of the new install!

    I am getting a quote on the new install and will ensure the new boiler header and near boiler piping is is redone with black pipe.

    I was planning to discuss with the contractor the following options-

    dual risers
    oversized drop headers
    King valves on the mains and return.
    Any other discussion points i should bring up?

  • KC_Jones
    KC_Jones Member Posts: 5,742
    Do you know what type of 2 pipe system you have? Some orifice systems had oversized radiation and the boiler gets sized to 80% of the installed radiation. That boiler does seem small if you have 408, but if it’s working I’d be hesitant to go much bigger.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Gsmith
    Gsmith Member Posts: 433
    Make sure your contract includes skimming the boiler, several times, until all oils are eliminated from the boiler water.
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    If the old boiler heated all the radiators evenly, I would NOT increase the boiler size. Could be the well insulated and short header needs little pickup. Smaller modern boilers have less volume and the jackets hold in heat better than older boilers that the sizing was calculated from.

    Also, I honestly think radiators regularly underperform (EDR is not an exact science) and not all radiator perfectly match the standardized pictures in the guides and I think it’s easy to make a mistake. Painted or not, coating or not. Paint color, distance from the wall, wall material, floor material, if it heat fully before the trap or vent closes. EDR calcs assume 2psi @ 218F no 212F @ 0psi before it builds pressure.

    Also keep in mind that the vent jumps from a 5” or 6” from a 35 to a 40 or 45, so the chimney capacity needs to be looked at.
  • garrettgjp
    garrettgjp Member Posts: 26
    Thanks all for the input!

    @KC_Jones I don't know if "standard" 2-pipe is the correct term but that is how I would describe it with my limited background in steam systems. It is definitely not an orifice or vapor system. I am a little hesitant to go bigger too since generally the system has been working and heating the house ok.

    Evaluating the heating of the house is a little bit harder considering 2nd floor is an apartment we rent out (duplex). Generally there aren't a lot of complaints but I have observed renters putting space heaters in the floor bedrooms when I've been upstairs addressing other issues... I'm in the midwest and people don't generally complain too much. I've checked in with every renter throughout the winter months asking if the heat is ok or if the have any questions about adjusting the rads, finding a comfortable setting, etc. Over the last few years the biggest complaint I get is during the shoulder seasons - bedrooms cold, living/dining room is comfortable.

    @Gary Smith Thanks I'll definitely ask about multiple skims and the skim port.

    @mikeg2015 Thank you! All good considerations especially the chimney vent. I'll ask the contractor about that as well.