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Help with Sizing a Boiler

Hi all.  Am new to heating help and new to steam heat in general.  Could anyone give me some input into sizing a replacement boiler for a parallel flow one-pipe steam system?  I live in a 1932 home currently with an American Standard oil burner (maybe from 1975?) and am in the middle of a gas conversion.

Current EDR = 407.5 sq ft (my contractor measures 427 sq ft).

Pipes are NOT insulated but I plan to insulate the mains.

There are two caps off the mains to suggest old radiators that were disconnected but they're capped at the mains.

My calculation:

407.5 x 240 x 1.33 pick up factor (assuming a reinsulate the mains) = 131 MBTU D.O.E.

My contractor is using a 1.5 pick up factor because he states that even though I reinsulate the mains, the rest of the pipes in the walls are not insulated.  So his calculation would give a DOE = 147 MBTU.

My contractor therefore recommends a Weil McLain EG-55 Steam which would give a DOE=167 with a net IBR=125 and so can handle the 147 MBTU load.  He thinks that even though it's slightly oversized, it's not so much that short cycling will not be a problem.

I noticed that the Weil McLain EG-50 Steam has a DOE =145 with a Net IBR=109.

I have three questions:

1)  Is it true that the pickup factor of 1.5 is needed even if I reinsulate the mains since the pipes in the wall remain uninsulated?

2)  If a pickup factor of only 1.33 is needed, will buying the EG-55 still be okay; in other words will I not have to worry about short cycling and ineffieciency?

3) Even if I need to use a pick up factor of 1.5 and I need to heat a system requiring 147 MBTU, would it be just as good to still go with the smaller boiler (EG 50 capable of delivering a DOE of 145) so that I get long heating cycles with radiators that are slowly heated (I'm thinking of Dave Brunnell's article, "Taking Another Look at Steam Boiler Sizing Methods")?

Thanks to all for all your contributions on the wall.  Learning about this stuff is addicting.


  • Jamie HallJamie Hall Member Posts: 6,653
    Size your boiler

    based on the EDR rating of the boiler.  It is way too much hassle to run through all the conversions and pickup factors etc.  They are already included in the EDR rating -- and you have the information you need for that.

    And no, you don't need to adjust the EDR for the uninsulated risers (although it would be nice to insulate them, but it isn't necessary).  You DO need to insulate your mains, however.

    You need to match the boiler size to the EDR as closely as you can; slightly oversize is not as bad as slightly undersize.  Short cycling on pressure really isn't that inefficient -- and in any case will only happen if your boiler is significantly oversize (say 10 percent or more) and you can't down fire it, or your main venting is poor, or you are coming back out of a deep (say more than 5 degree F) setback.

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

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Charlie from wmassCharlie from wmass Member Posts: 3,911
    Whether you use your edr or

    your contractors edr the boiler to use would be the EG50. This is of course assuming you do not have any strange or excessive piping. A few risers in the wall would not be enough to bump you up to the EG55.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • SteamworkSSteamworkS Member Posts: 14
    EDR for Weil McLain

    Thanks for the input. Does anyone know the EDR ratings of the Weil-McLain EG 50 and EG 55?
  • JStarJStar Member Posts: 2,668
    edited April 2014

    I've been using a 15% piping factor for insulated mains with great success. But, not everyone is that daring! I would use an EG-45. Well, I wouldn't use a Weil McLain at all, but that is a different, and heated, topic altogether.

    EDIT: Using a smaller boiler size will require the rest of the system to be in perfect operating condition; ie: better-than-recommended piping, massive main venting, correct radiator venting, and low pressures.

    Just in case you wanted another opinion with a completely different model/size to muddle your decision...
    - Joe Starosielec
    [email protected]
  • Charlie from wmassCharlie from wmass Member Posts: 3,911
    here you go

    454, 521 edr's
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • ChrisJChrisJ Member Posts: 8,611
    edited April 2014
    Only a homeowner.

    I agree with Jstar in regards to the smaller pickup factor.  In fact if I had to redo my system over again I might not use any pickup factor.  I'm currently running an EG-45 connected to 392sqft of radiation and part of me wishes I had an EG-40 instead. 

     Even though my connected radiation is exactly matched to the boiler with a 1.33 pickup factor I can build pressure, though it takes a long time.  This is because the boiler is 33% too big for absolutely no reason in my opinion.  It's also because I have two TRVs that cut off 100sqft of radiation at times, but that's another story.

     If I was you I would insulate all of the piping with 1" or larger pipe insulation, don't wrap fiberglass bats around things.   I would then choose an EG-45 or an EG-50 if you wanted to play it safe but never an EG-55.  The EG-55 is too big and it will matter for as long as you own the boiler.  If your piping is all made perfect and you insulate everything, vent the mains extremely fast and vent the radiators appropriately  I feel the EG-45 will work beautifully.  The EG-50 won't be as picky but the EG-55 will do nothing but waste money and make a lot of noise from building pressure every cycle.

    I would recommend asking about the proposed piping on here before any work is done just to be safe and don't forge to skim!  After the new boiler is running it's going to take a lot of time and skimming to get all of the oils out.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment

    Steam system pictures
    Central air project pictures
  • Charlie from wmassCharlie from wmass Member Posts: 3,911
    think about geography and room temperature

    If you do not have a boiler that can build pressure and you do not use TRV's heavily you will not like the way your system behaves if it is undersized. Steam will often find the one radiator you really want to heat up and not go there if the boiler is undersized. Note that the EDR rating for boilers has a 1.33 pick up already firgured into it. The only time I add a pick up factor is when reverse engineering to figure out the fire rating for a given system with either a gas orfice or oil nozzle.  Too long of a run time during a heat cycle also wastes fuel. And you are cold while wasting fuel which is worse then an oversized boiler wasting fuel by short cycling, but keeping you warm.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • ChrisJChrisJ Member Posts: 8,611
    edited April 2014

    Hi Charlie,

    I've thought about it many times and because we heat our piping which is insulated first and then once all of that is hot we proceed to heat the radiation which is typically oversized for the room I feel a pickup factor is unnecessary. TRVs are not required to keep an undersized boiler inline, very slow radiator vents are. If you vent the radiators slow they will all heat together without any of them becoming a hog, in theory. Even with my current setup if I vent certain radiators really fast I will loose heat in rooms.

    As I've said many times I'm a homeowner not a pro and have only worked on a few steam systems. This is simply what I've observed and believe to be correct, however I do believe Dave Brunell agrees with me at least for the most part.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment

    Steam system pictures
    Central air project pictures
  • SteamworkSSteamworkS Member Posts: 14
    Thanks guys

    Thanks for everyone's input.

    I'll size the new boiler based on it's rated EDR and go with the EG-50; I'm too chicken to go with the EG-45.  I'll ignore the pickup factor since it's factored into the EDR rating.

    I'll insulate all the near-boiler piping once it's redone and the mains with 1" fiberglass plus I'd like to have it covered with the childer's mastik that I saw in a picture by Gerry Gill in the past.

    Anyone know someone who does this in Westchester County, New York?
  • SWEISWEI Member Posts: 7,356
    It would be interesting to know

    if the connected EDR is actually 407 or 427.
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